P5 - Space For Reflection Flashcards
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P5 - Space for Reflection
What happens if the distance from a planet is doubled (gravity)?
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Gravitational force decreases by a factor of 4 (22)
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P5 - Space for Reflection
What is the formula for gravity?
A
F ∝ 1/d²
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What does gravity provide to ensure planets orbit in a circular motion?
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A centripetal force - it is directed to the centre of the circle.
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What happens if a planet is twice as close (gravity)?
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Gravitational force increases by a factor of 4
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What is speed?
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How fast something’s going
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Why is velocity a more useful measure of motion?
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Because it describes both the speed and direction
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What is a scalar quantity?
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A quantity like speed that has only a number
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What are some examples of scalar quantities?
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Speed Mass Temperature Time Length
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What is a vector quantity?
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A quantity like velocity that has a direction and a number
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What are some examples of vector quantities?
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Velocity Force Displacement Acceleration Momentum
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What is relative speed?
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How fast something is going relative to something else.
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What will the relative speed be of a car going the same way as you?
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The car will have a small speed relative to your car
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What will the relative speed be of a car going the opposite direction to you?
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The car will have a bigger speed relative to your car.
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What happens to the vectors if two things are moving in the same directions?
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The vectors are added
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What happens to the vectors if two things are moving in the same directions?
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Vectors are subtracted
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What is used if an object mov against the current e.g. Across the wind?
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Pythagoras theorem. Velocity is needed.
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What does u stand for in the equations of motion?
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Initial velocity
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What does v stand for in the equations of motion?
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Final velocity
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What does s stand for in the equations of motion?
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Distance (or displacement)
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What does t stand for in the equations of motion?
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Time
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What does a stand for in the equations of motion?
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Acceleration
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What is a projectile?
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Something that is projected, or dropped and only has Earth’s gravitational field acting on it.
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Give some examples of projectiles…
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Golf ball, missile, football.
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What is a trajectory?
A
The path a projectile takes
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What shape is a projectile trajectory?
Parabolic
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What does the distance a projectile travels depend on?
Angle it is launched at.
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At what angle will a projectile travel the furthest?
45 degrees
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What happens to the projectile if launched at less than 45 degrees?
Won't travel as far
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What happens to the distance travelled by the projectile if launched at more than 45 degrees?
Projectile will take longer to hit ground and won't travel as far
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How is motion split up?
Into horizontal and vertical
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How does gravity affect motion?
Acts downwards - doesn't affect horizontal at all.
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Why does an object launched horizontally accelerate vertically?
Due to gravity. Has no horizontal acceleration (velocity stays same).
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How is the resultant velocity calculated?
The vector sum of the separate motions
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What happens when an object exerts a force on another object?
It always experiences a force in return.
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What is an interaction pair?
When an object exerts a force and experiences one in return
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What is Newton's Third Law of Motion?
If object A exerts a force in object B, then object B exerts an equal and opposite force on object A.
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What is the equation for momentum?
Mass x velocity
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What are the units for momentum?
Kg m/s
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In a collision when no other forces are involved, what happens to momentum?
It is conserved
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What does coalesce mean?
Join together (when two objects collide)
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What does m1 stand for?
Mass of first object
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What does m2 stand for?
Mass of second object
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What does u1 stand for?
Velocity of first object
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What does u2 stand for?
Velocity of second object
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What does v stand for in the momentum equation?
Velocity of combined objects
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If the forces are equal how does anything move?
The forces are acting on different objects
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What does kinetic theory say that gases consist of?
Very small particles constantly moving in random directions.
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How much space do the gas particles take up?
Hardly any - most of gas is empty space.
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What do the particles in a gas do with each other?
Constantly collide and bounce off each other (or off the walls).
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Why do gas particles exert a force when they collide?
Because gas particles have some mass.
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What happens with gas particles in a sealed container?
Gas particles smash against container walls - creates outward pressure.
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What happens when the same volume of gas is put in a bigger container?
Larger volume decreases pressure. Fewer collisions between gas particles and walls.
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What happens when the volume is reduced in a gas container?
Particles are more squashed - hit walls more often - pressure increase.
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What does the pressure of a gas depend on?
How fast the particles are moving and how often they hit the container walls.
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What happens if you heat a gas?
Particles move faster and have more kinetic energy. Hit container wall more often, creating more pressure.
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What happens if a gas is cooled?
Particles have less kinetic energy - hit walls with less force and less often - pressure reduced.
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As well as moving and having a mass, what else do gas particles have?
Momentum
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What happens to momentum when gas particles hit the container walls?
Changes velocity and momentum - exerts force on container (pressure).
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What is an orbit?
A balance between the forward motion of an object and a force pulling it inwards. (centripetal)
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What provides the centripetal force so the planets orbit the Sun in orbits?
Gravitational force between each planet and the sun.
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There must be a force acting on it if...
An object is travelling in a circle and constantly changing direction.
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Why does the moon orbit the earth?
Because of the centripetal force produced by the gravitational force between Earth and Moon.
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What happens to gravity the closer you get to a star or planet?
Stronger force of attraction
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What does a stronger force of attraction mean the planets do?
Planets nearer sun move faster and cover orbits quicker.
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In addition to planets/stars, what else are held in orbit by gravity?
Moons, artificial satellites and space stations.
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What type of orbit do periodic comets have?
Highly elliptical orbits
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What happens to comets when they are closer to the sun?
Greater the gravitational force of attraction. Travel much faster here.
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What type of orbit do communications satellites need?
Quite high orbit. Above equator. Orbit once every 24hrs.
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Whereabouts do communications satellites stay in relation to the earth?
Over same point. Earth rotates with them.
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What is the name given to communications satellites?
Geostationary artificial satellites/geosynchronous satellites.
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What are geostationary satellites ideal for?
Telephone, TV and radio.
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Why are geostationary satellites ideal for TV, radio and telephone?
Stay at same point above Earth and can transfer signals from one side of earth to another in fraction of a second.
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Why are geostationary satellites not used for weather and spying satellites?
Too high and too stationary
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What kind of orbit do weather and spying satellites need?
Low polar orbit, passing over both poles.
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What happens in a low polar orbit?
Satellite sweeps over both poles whilst earth rotates beneath it.
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What is the difference for low polar orbit satellites in terms of gravity?
Much closer to earth = pull of gravity stronger and move faster.
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How long is the orbit of a low polar orbit satellite?
Often under 2 hours
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What happens each time the low polar orbit satellite orbits and what does this allow?
It can scan the next bit of globe and allows whole surface. To be monitored each day.
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What wave do communications to and from satellites use?
Microwaves
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How are signals for satellite TV and phones transmitted?
From transmitter. Picked up by satellite receiver dish orbiting 1000s of km above Earth. Satellite transmits signal back to earth in different direction and received by satellite dish on ground. OR satellites receiving signal retransmit it to other satellites and eventually back to earth.
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What type of frequency do microwaves have?
High frequency - over 3,000MHz (3GHz)
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How can microwaves reach distant parts of the planet?
They pass easily through the atmosphere to satellites orbiting Earth.
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How is the frequency different for low orbit satellites than those in a geostationary orbit?
Those in low orbit use lower frequencies.
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Why do satellite signals weaken?
They travel over long distances (losing intensity and picking up interference).
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Why are digital signals used for satellites?
High quality and don't suffer as much interference.
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What is the magnification formula?
image size ÷ object size
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What type of lenses do magnifying glasses use to create images?
Convex lenses
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Where must the object being magnified be placed?
Closer to the lens than the focal length
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What image is produced from a magnifying glass?
Virtual image
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What are the stages when photographing an object?
Light from object travels to camera and is refracted by lens, forming an image on the light sensor.
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What is the image type when taking a photograph?
Real image - light rays actually meet
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What is the image size when taking photos? Why?
Smaller than object because object's further away than focal length of lens
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How does the image appear in a photo?
Inverted (upside down)
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Where is an object positioned for a projector?
Object much closer than focal length
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What size if the image from a projector?
Larger
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How does the object need to be placed when projecting it?
Upside down and very close to lens
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What happens to light when an object is projected?
Refracted by lens
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What image is produced when an object is projected?
Real, inverted and magnified image on screen
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When will an image be in focus?
When the light that forms the image converges on the screen or sensor
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How is the image focused in cameras/projectors?
By moving the lens closer to or further from the object
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The closer the object to the lens...
The further from the lens the image is formed
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If 2 speakers both play the same note at exactly the same time where does constructive interference occur?
When distance travelled by waves from both speakers is either same or different by a WHOLE NUMBER of wavelengths.
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If 2 speakers both play the same note at exactly the same time, where does destructive interference occur?
When difference in distance travelled by waves from both speakers is 1/2 wavelength, 1 1/2 wavelength, 2 1/2 wavelength, etc.
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What is path difference?
Difference in distance travelled by waves from both speakers
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What is a pattern of loud and quiet called?
Interference pattern
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What is an interference pattern?
Pattern of constructive (loud) and destructive (quiet) interference. Applies for all type of waves.
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What do you need to get a stable interference pattern?
A coherent wave source
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What does it mean to have a coherent wave source?
1. Waves at same frequency/wavelength
2. Waves in phase (troughs and crests line up)
3. Waves have same amplitude
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What is the coherent source for light?
Monochromatic light (type produces interference patterns)
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Why are EM waves with different frequencies used to transmit different types of communication signals?
Thay behave differently in the atmosphere
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What happens to signals below 30MHz?
Radiowaves reflected off ionosphere, allowing wave to travel longer distances and deal with Earth's curvature.
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What happens to signals between 30MHz and 30GHz?
Radiowaves and Microwaves pass straight through atmosphere so transmissions must be in line of sight (can't reflect off atmosphere).
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What happens to signals above 30GHz?
Rain and dust in atmosphere absorb and scatter microwaves. This reduces signal strength, so highest frequency that can be used for satellite transmission is about 30GHz.
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If 2 speakers both play the same note at exactly the same time, depending on where you stand, what do you hear?
Either loud sound or almost nothing
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If 2 speakers both play the same note at exactly the same time what is heard in areas of constructive interference?
Loud sound - waves in phase and amplitude doubles
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If 2 speakers both play the same note at exactly the same time what is heard in areas of destructive interference?
Almost no sound - waves exactly out of phase, cancel out.
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What happens to all waves as they pass an object or through a narrow gap?
They diffract
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What is classed as a 'narrow gap'?
One which is about the same size as the wavelength.
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What achieves the maximum amount of diffraction?
When size of gap = wavelength of wave
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Why are long-wave radiowaves great for broadcasting?
Can diffract over hills, through tunnels and over horizon.
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How are terrestrial TV and radio signals transmitted?
Using radiowaves (and a dish) and are received by an aerial.
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How is a narrow beam produced when transmitting microwaves or radiowaves?
Dishes are many times larger than wavelength so waves don't diffract much - producing a narrow beam.
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What do all waves cause in a medium?
Some kind of disturbance.
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What do water waves disturb?
Water particles
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What do sound waves disturb?
Air particles
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What do EM waves disturb?
Electric and Magnetic fields
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What is constructive interference?
Waves disturb in the same direction and reinforce each other.
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What is destructive interference?
Waves disturb in opposite directions and cancel each other out.
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What is the total amplitude of a wave at any point?
The sum of the displacements (taking into account direction) of the wave at that point.
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When do you get interference patterns?
When waves of equal frequency or wavelength overlap.
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What happens when a wavefront passes through a gap?
Light from each point along the gap diffracts.
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What must a gap be so that light will diffract?
About the same size as the wavelength of light.
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What does an interference pattern create?
A bright central fringe, with alternating dark and bright fringes on either side.
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What 2 theories were there in the 17th Century to explain the nature of light?
* Particle theory - Isaac Newton
* Wave theory - Christiaan Huygens
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What could the particle theory explain?
Reflection and refraction
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What could the particle theory not explain?
Diffraction and interference
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Why could the particle theory not explain diffraction and interference?
They are both unique to waves
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What did Thomas Young's double slit experiment show?
That light could diffract (through 2 narrow slits) and interfere (to form interference patterns on screen).
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What did Thomas Young's Double Slit experiment involve?
A coherent light source (e.g. laser) shone through two narrow slits.
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What is now accepted about light?
It shows properties of a wave (diffraction, interference and polarisation).
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What type of wave are EM waves?
Transverse - vibrations at 90º to direction of travel.
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How can you make (imitate) a transverse wave?
Shake a rope up and down/side to side, or in a mixture of directions.
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What is plane polarisation?
Filtering out all vibrations of waves except a particular direction.
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What is ordinary light a mixture of?
Vibrations in different directions
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What does passing light through a polarising filter do?
Filter only transmits vibrations in one particular direction.
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What is plane polarised light made up of?
Vibrations in one direction only
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What happens when light is reflected from some surfaces like water?
It is partly plane polarised
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What do polaroid sunglasses act as?
Polarising filters - can filter out reflected glare from sea/snow
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What is refraction?
When waves change direction as they enter a different medium
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What causes refraction?
Change of speed in waves which causes change in wavelength - NO CHANGE IN FREQ
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What happens when a wave passes the boundary between 2 substances?
Changes speed
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How does the wave refract if the wave speed decreases?
Wave bends towards normal
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How does the wave refract when the wave speed increases?
Wave bends away from the normal.
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What does light slow down to when it enters glass?
2/3 normal speed in air (about 2x108m/s rather than 3 x 108m/s)
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What is refractive index?
Ratio of speed of light in a vacuum to the speed of light in a medium.
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What is the refractive index basically a measure of?
The amount of bending
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The higher the refractive index...
The more the light bends when it enters/leaves the medium.
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What happens when waves hit a boundary along the normal (exactly 90º)?
No change in direction - change in speed and wavelength
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How is the absolute refractive index of a material defined?
speed of light (c) ÷ speed of light in medium (v)
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What is the refractive index of glass and why?
High (around 1.5) - light slows down a lot in glass
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What is the refractive index of water compared to glass?
Lower (around 1.33) - light slows down less in water than in glass.
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What is the refractive index of air?
About same as in a vacuum - 1.
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Why are different colours of light refracted by different amounts?
They travel at different speeds in any given medium (but same in a vacuum).
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Which colour of light slows down the least?
Red - refracted least and has lowest refractive index (1.514...)
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What colour of light is refracted most?
Blue - higher refractive index (1.523...)
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What is used to make different colours of light emerge at different angles?
A prism
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What can a prism do to light?
Make different colours of white light refract, producing a spectrum - dispersion.
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What is dispersion?
When a spectrum is produced to show colours of rainbow.
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When does TIR only happen?
When light travels from a more dense medium with a higher RI to a less dense medium with a lower RI.
E.g. Glass to water
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What is TIR?
When angle of incidence is greater than critical angle, ray of light won't come out but is reflected back into medium.
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What happens when angle of incidence is less than critical angle?
Most light passes through into air but little bit is internally reflected.
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What happens when angle of incidence is equal to critical angle?
Emerging ray travels along the surface. Quite a bit internal reflection.
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What happens when angle of incidence is greater than critical angle?
No light comes out - all totally internally reflected
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Different media have different critical angles so the higher the refractive index of the medium....
The lower the critical angle will be.
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What is the critical angle for glass?
About 42º
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Why is a critical angle of 42 useful in glass?
45º can be used to get TIR e.g. optical fibres
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What can TIR be used in?
Optical fibres, prisms in binoculars, reflectors, road signs and cat's eyes.
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What is a real image?
Where light rays from an object come together to form an image on a screen (inc. retina - eye's screen).
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What can you do to real images?
Project them onto a screen
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What is a virtual image?
When rays diverge so light from object appears to come from a different place.
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What can't you do with a virtual image?
Project it onto a screen
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What type of image is looking in a mirror?
Virtual - object (face) appears behind mirror.
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What is the image when you look through a magnfiying glass?
Virtual - appears bigger and further away than it actually is.
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What 4 things describe an image?
1. How big compared to original
2. Real or virtual
3. Upright or inverted
4. Where it is (in relation to lens and focal point)
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What shape is a converging lens?
Convex
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What does a convex lens do to light?
Rays converge to a focus
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What happens if the rays entering the lens are parallel to each other and to the principal axis?
Focuses them at a point - focal point
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What is the focal length?
Distance between centre of lens and focal point
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What happens to the speed of a ray travelling parallel to the principal axis?
Slows down upon entry and bends towards normal.
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What happens to a ray travelling parallel to the principal axis when it hits the 'glass to air' boundary?
Speeds up - bends away from normal
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When a ray is travelling parallel to the principal axis, what does the curvature of the lens mean?
All the rays hitting different parts of lens are bent towards some focal point to form image.
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What does a ray passing through the optical centre of the lens appear to do?
Pass straight through
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How does a ray passing through the optical centre of the lens exit?
At same angle as entry but on opposite side to principal axis, so bent same amount - opposite direction.
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Describe how a convex lens can work in the opposite way...
Turns diverging rays into parallel light
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What type of image can convex lenses produce?
Real or virtual depending on how close object is to lens
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What will an object at 2F produce?
Real, inverted image, same size as object and at 2F
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What will an object between F and 2F produce?
Real, inverted image bigger than object and beyond 2F
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What will an object nearer than F produce?
Virtual image, right way up, bigger than object and on same side of lens.
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Gravitational force decreases by a factor of 4 (22)
What happens if the distance from a planet is doubled (gravity)?
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F ∝ 1/d²
What is the formula for gravity?
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A centripetal force - it is directed to the centre of the circle.
What does gravity provide to ensure planets orbit in a circular motion?
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Gravitational force increases by a factor of 4
What happens if a planet is twice as close (gravity)?
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How fast something's going
What is speed?
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Because it describes both the speed and direction
Why is velocity a more useful measure of motion?
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A quantity like speed that has only a number
What is a scalar quantity?
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Speed Mass Temperature Time Length
What are some examples of scalar quantities?
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A quantity like velocity that has a direction and a number
What is a vector quantity?
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Velocity Force Displacement Acceleration Momentum
What are some examples of vector quantities?
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How fast something is going relative to something else.
What is relative speed?
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The car will have a small speed relative to your car
What will the relative speed be of a car going the same way as you?
212
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The car will have a bigger speed relative to your car.
What will the relative speed be of a car going the opposite direction to you?
213
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The vectors are added
What happens to the vectors if two things are moving in the same directions?
214
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Vectors are subtracted
What happens to the vectors if two things are moving in the same directions?
215
# P5 - Space for Reflection
Pythagoras theorem. Velocity is needed.
What is used if an object mov against the current e.g. Across the wind?
216
# P5 - Space for Reflection
Initial velocity
What does u stand for in the equations of motion?
217
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Final velocity
What does v stand for in the equations of motion?
218
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Distance (or displacement)
What does s stand for in the equations of motion?
219
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Time
What does t stand for in the equations of motion?
220
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Acceleration
What does a stand for in the equations of motion?
221
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Something that is projected, or dropped and only has Earth's gravitational field acting on it.
What is a projectile?
222
# P5 - Space for Reflection
Golf ball, missile, football.
Give some examples of projectiles...
223
# P5 - Space for Reflection
The path a projectile takes
What is a trajectory?
224
# P5 - Space for Reflection
Parabolic
What shape is a projectile trajectory?
225
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Angle it is launched at.
What does the distance a projectile travels depend on?
226
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45 degrees
At what angle will a projectile travel the furthest?
227
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Won't travel as far
What happens to the projectile if launched at less than 45 degrees?
228
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Projectile will take longer to hit ground and won't travel as far
What happens to the distance travelled by the projectile if launched at more than 45 degrees?
229
# P5 - Space for Reflection
Into horizontal and vertical
How is motion split up?
230
# P5 - Space for Reflection
Acts downwards - doesn't affect horizontal at all.
How does gravity affect motion?
231
# P5 - Space for Reflection
Due to gravity. Has no horizontal acceleration (velocity stays same).
Why does an object launched horizontally accelerate vertically?
232
# P5 - Space for Reflection
The vector sum of the separate motions
How is the resultant velocity calculated?
233
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It always experiences a force in return.
What happens when an object exerts a force on another object?
234
# P5 - Space for Reflection
When an object exerts a force and experiences one in return
What is an interaction pair?
235
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If object A exerts a force in object B, then object B exerts an equal and opposite force on object A.
What is Newton's Third Law of Motion?
236
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Mass x velocity
What is the equation for momentum?
237
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Kg m/s
What are the units for momentum?
238
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It is conserved
In a collision when no other forces are involved, what happens to momentum?
239
# P5 - Space for Reflection
Join together (when two objects collide)
What does coalesce mean?
240
# P5 - Space for Reflection
Mass of first object
What does m1 stand for?
241
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Mass of second object
What does m2 stand for?
242
# P5 - Space for Reflection
Velocity of first object
What does u1 stand for?
243
# P5 - Space for Reflection
Velocity of second object
What does u2 stand for?
244
# P5 - Space for Reflection
Velocity of combined objects
What does v stand for in the momentum equation?
245
# P5 - Space for Reflection
The forces are acting on different objects
If the forces are equal how does anything move?
246
# P5 - Space for Reflection
Very small particles constantly moving in random directions.
What does kinetic theory say that gases consist of?
247
# P5 - Space for Reflection
Hardly any - most of gas is empty space.
How much space do the gas particles take up?
248
# P5 - Space for Reflection
Constantly collide and bounce off each other (or off the walls).
What do the particles in a gas do with each other?
249
# P5 - Space for Reflection
Because gas particles have some mass.
Why do gas particles exert a force when they collide?
250
# P5 - Space for Reflection
Gas particles smash against container walls - creates outward pressure.
What happens with gas particles in a sealed container?
251
# P5 - Space for Reflection
Larger volume decreases pressure. Fewer collisions between gas particles and walls.
What happens when the same volume of gas is put in a bigger container?
252
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Particles are more squashed - hit walls more often - pressure increase.
What happens when the volume is reduced in a gas container?
253
# P5 - Space for Reflection
How fast the particles are moving and how often they hit the container walls.
What does the pressure of a gas depend on?
254
# P5 - Space for Reflection
Particles move faster and have more kinetic energy. Hit container wall more often, creating more pressure.
What happens if you heat a gas?
255
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Particles have less kinetic energy - hit walls with less force and less often - pressure reduced.
What happens if a gas is cooled?
256
# P5 - Space for Reflection
Momentum
As well as moving and having a mass, what else do gas particles have?
257
# P5 - Space for Reflection
Changes velocity and momentum - exerts force on container (pressure).
What happens to momentum when gas particles hit the container walls?
258
# P5 - Space for Reflection
A balance between the forward motion of an object and a force pulling it inwards. (centripetal)
What is an orbit?
259
# P5 - Space for Reflection
Gravitational force between each planet and the sun.
What provides the centripetal force so the planets orbit the Sun in orbits?
260
# P5 - Space for Reflection
An object is travelling in a circle and constantly changing direction.
There must be a force acting on it if...
261
# P5 - Space for Reflection
Because of the centripetal force produced by the gravitational force between Earth and Moon.
Why does the moon orbit the earth?
262
# P5 - Space for Reflection
Stronger force of attraction
What happens to gravity the closer you get to a star or planet?
263
# P5 - Space for Reflection
Planets nearer sun move faster and cover orbits quicker.
What does a stronger force of attraction mean the planets do?
264
# P5 - Space for Reflection
Moons, artificial satellites and space stations.
In addition to planets/stars, what else are held in orbit by gravity?
265
# P5 - Space for Reflection
Highly elliptical orbits
What type of orbit do periodic comets have?
266
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Greater the gravitational force of attraction. Travel much faster here.
What happens to comets when they are closer to the sun?
267
# P5 - Space for Reflection
Quite high orbit. Above equator. Orbit once every 24hrs.
What type of orbit do communications satellites need?
268
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Over same point. Earth rotates with them.
Whereabouts do communications satellites stay in relation to the earth?
269
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Geostationary artificial satellites/geosynchronous satellites.
What is the name given to communications satellites?
270
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Telephone, TV and radio.
What are geostationary satellites ideal for?
271
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Stay at same point above Earth and can transfer signals from one side of earth to another in fraction of a second.
Why are geostationary satellites ideal for TV, radio and telephone?
272
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Too high and too stationary
Why are geostationary satellites not used for weather and spying satellites?
273
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Low polar orbit, passing over both poles.
What kind of orbit do weather and spying satellites need?
274
# P5 - Space for Reflection
Satellite sweeps over both poles whilst earth rotates beneath it.
What happens in a low polar orbit?
275
# P5 - Space for Reflection
Much closer to earth = pull of gravity stronger and move faster.
What is the difference for low polar orbit satellites in terms of gravity?
276
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Often under 2 hours
How long is the orbit of a low polar orbit satellite?
277
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It can scan the next bit of globe and allows whole surface. To be monitored each day.
What happens each time the low polar orbit satellite orbits and what does this allow?
278
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Microwaves
What wave do communications to and from satellites use?
279
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From transmitter. Picked up by satellite receiver dish orbiting 1000s of km above Earth. Satellite transmits signal back to earth in different direction and received by satellite dish on ground. OR satellites receiving signal retransmit it to other satellites and eventually back to earth.
How are signals for satellite TV and phones transmitted?
280
# P5 - Space for Reflection
High frequency - over 3,000MHz (3GHz)
What type of frequency do microwaves have?
281
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They pass easily through the atmosphere to satellites orbiting Earth.
How can microwaves reach distant parts of the planet?
282
# P5 - Space for Reflection
Those in low orbit use lower frequencies.
How is the frequency different for low orbit satellites than those in a geostationary orbit?
283
# P5 - Space for Reflection
They travel over long distances (losing intensity and picking up interference).
Why do satellite signals weaken?
284
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High quality and don't suffer as much interference.
Why are digital signals used for satellites?
285
# P5 - Space for Reflection
image size ÷ object size
What is the magnification formula?
286
# P5 - Space for Reflection
Convex lenses
What type of lenses do magnifying glasses use to create images?
287
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Closer to the lens than the focal length
Where must the object being magnified be placed?
288
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Virtual image
What image is produced from a magnifying glass?
289
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Light from object travels to camera and is refracted by lens, forming an image on the light sensor.
What are the stages when photographing an object?
290
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Real image - light rays actually meet
What is the image type when taking a photograph?
291
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Smaller than object because object's further away than focal length of lens
What is the image size when taking photos? Why?
292
# P5 - Space for Reflection
Inverted (upside down)
How does the image appear in a photo?
293
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Object much closer than focal length
Where is an object positioned for a projector?
294
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Larger
What size if the image from a projector?
295
# P5 - Space for Reflection
Upside down and very close to lens
How does the object need to be placed when projecting it?
296
# P5 - Space for Reflection
Refracted by lens
What happens to light when an object is projected?
297
# P5 - Space for Reflection
Real, inverted and magnified image on screen
What image is produced when an object is projected?
298
# P5 - Space for Reflection
When the light that forms the image converges on the screen or sensor
When will an image be in focus?
299
# P5 - Space for Reflection
By moving the lens closer to or further from the object
How is the image focused in cameras/projectors?
300
# P5 - Space for Reflection
The further from the lens the image is formed
The closer the object to the lens...
301
# P5 - Space for Reflection
When distance travelled by waves from both speakers is either same or different by a WHOLE NUMBER of wavelengths.
If 2 speakers both play the same note at exactly the same time where does constructive interference occur?
302
# P5 - Space for Reflection
When difference in distance travelled by waves from both speakers is 1/2 wavelength, 1 1/2 wavelength, 2 1/2 wavelength, etc.
If 2 speakers both play the same note at exactly the same time, where does destructive interference occur?
303
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Difference in distance travelled by waves from both speakers
What is path difference?
304
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Interference pattern
What is a pattern of loud and quiet called?
305
# P5 - Space for Reflection
Pattern of constructive (loud) and destructive (quiet) interference. Applies for all type of waves.
What is an interference pattern?
306
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A coherent wave source
What do you need to get a stable interference pattern?
307
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1. Waves at same frequency/wavelength
2. Waves in phase (troughs and crests line up)
3. Waves have same amplitude
What does it mean to have a coherent wave source?
308
# P5 - Space for Reflection
Monochromatic light (type produces interference patterns)
What is the coherent source for light?
309
# P5 - Space for Reflection
Thay behave differently in the atmosphere
Why are EM waves with different frequencies used to transmit different types of communication signals?
310
# P5 - Space for Reflection
Radiowaves reflected off ionosphere, allowing wave to travel longer distances and deal with Earth's curvature.
What happens to signals below 30MHz?
311
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Radiowaves and Microwaves pass straight through atmosphere so transmissions must be in line of sight (can't reflect off atmosphere).
What happens to signals between 30MHz and 30GHz?
312
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Rain and dust in atmosphere absorb and scatter microwaves. This reduces signal strength, so highest frequency that can be used for satellite transmission is about 30GHz.
What happens to signals above 30GHz?
313
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Either loud sound or almost nothing
If 2 speakers both play the same note at exactly the same time, depending on where you stand, what do you hear?
314
# P5 - Space for Reflection
Loud sound - waves in phase and amplitude doubles
If 2 speakers both play the same note at exactly the same time what is heard in areas of constructive interference?
315
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Almost no sound - waves exactly out of phase, cancel out.
If 2 speakers both play the same note at exactly the same time what is heard in areas of destructive interference?
316
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They diffract
What happens to all waves as they pass an object or through a narrow gap?
317
# P5 - Space for Reflection
One which is about the same size as the wavelength.
What is classed as a 'narrow gap'?
318
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When size of gap = wavelength of wave
What achieves the maximum amount of diffraction?
319
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Can diffract over hills, through tunnels and over horizon.
Why are long-wave radiowaves great for broadcasting?
320
# P5 - Space for Reflection
Using radiowaves (and a dish) and are received by an aerial.
How are terrestrial TV and radio signals transmitted?
321
# P5 - Space for Reflection
Dishes are many times larger than wavelength so waves don't diffract much - producing a narrow beam.
How is a narrow beam produced when transmitting microwaves or radiowaves?
322
# P5 - Space for Reflection
Some kind of disturbance.
What do all waves cause in a medium?
323
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Water particles
What do water waves disturb?
324
# P5 - Space for Reflection
Air particles
What do sound waves disturb?
325
# P5 - Space for Reflection
Electric and Magnetic fields
What do EM waves disturb?
326
# P5 - Space for Reflection
Waves disturb in the same direction and reinforce each other.
What is constructive interference?
327
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Waves disturb in opposite directions and cancel each other out.
What is destructive interference?
328
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The sum of the displacements (taking into account direction) of the wave at that point.
What is the total amplitude of a wave at any point?
329
330
# P5 - Space for Reflection
When waves of equal frequency or wavelength overlap.
When do you get interference patterns?
331
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Light from each point along the gap diffracts.
What happens when a wavefront passes through a gap?
332
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About the same size as the wavelength of light.
What must a gap be so that light will diffract?
333
# P5 - Space for Reflection
A bright central fringe, with alternating dark and bright fringes on either side.
What does an interference pattern create?
334
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* Particle theory - Isaac Newton
* Wave theory - Christiaan Huygens
What 2 theories were there in the 17th Century to explain the nature of light?
335
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Reflection and refraction
What could the particle theory explain?
336
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Diffraction and interference
What could the particle theory not explain?
337
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They are both unique to waves
Why could the particle theory not explain diffraction and interference?
338
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That light could diffract (through 2 narrow slits) and interfere (to form interference patterns on screen).
What did Thomas Young's double slit experiment show?
339
# P5 - Space for Reflection
A coherent light source (e.g. laser) shone through two narrow slits.
What did Thomas Young's Double Slit experiment involve?
340
# P5 - Space for Reflection
It shows properties of a wave (diffraction, interference and polarisation).
What is now accepted about light?
341
# P5 - Space for Reflection
Transverse - vibrations at 90º to direction of travel.
What type of wave are EM waves?
342
# P5 - Space for Reflection
Shake a rope up and down/side to side, or in a mixture of directions.
How can you make (imitate) a transverse wave?
343
# P5 - Space for Reflection
Filtering out all vibrations of waves except a particular direction.
What is plane polarisation?
344
# P5 - Space for Reflection
Vibrations in different directions
What is ordinary light a mixture of?
345
# P5 - Space for Reflection
Filter only transmits vibrations in one particular direction.
What does passing light through a polarising filter do?
346
# P5 - Space for Reflection
Vibrations in one direction only
What is plane polarised light made up of?
347
# P5 - Space for Reflection
It is partly plane polarised
What happens when light is reflected from some surfaces like water?
348
# P5 - Space for Reflection
Polarising filters - can filter out reflected glare from sea/snow
What do polaroid sunglasses act as?
349
# P5 - Space for Reflection
When waves change direction as they enter a different medium
What is refraction?
350
# P5 - Space for Reflection
Change of speed in waves which causes change in wavelength - NO CHANGE IN FREQ
What causes refraction?
351
# P5 - Space for Reflection
Changes speed
What happens when a wave passes the boundary between 2 substances?
352
# P5 - Space for Reflection
Wave bends towards normal
How does the wave refract if the wave speed decreases?
353
# P5 - Space for Reflection
Wave bends away from the normal.
How does the wave refract when the wave speed increases?
354
# P5 - Space for Reflection
2/3 normal speed in air (about 2x108m/s rather than 3 x 108m/s)
What does light slow down to when it enters glass?
355
# P5 - Space for Reflection
Ratio of speed of light in a vacuum to the speed of light in a medium.
What is refractive index?
356
# P5 - Space for Reflection
The amount of bending
What is the refractive index basically a measure of?
357
# P5 - Space for Reflection
The more the light bends when it enters/leaves the medium.
The higher the refractive index...
358
# P5 - Space for Reflection
No change in direction - change in speed and wavelength
What happens when waves hit a boundary along the normal (exactly 90º)?
359
# P5 - Space for Reflection
speed of light (c) ÷ speed of light in medium (v)
How is the absolute refractive index of a material defined?
360
# P5 - Space for Reflection
High (around 1.5) - light slows down a lot in glass
What is the refractive index of glass and why?
361
# P5 - Space for Reflection
Lower (around 1.33) - light slows down less in water than in glass.
What is the refractive index of water compared to glass?
362
# P5 - Space for Reflection
About same as in a vacuum - 1.
What is the refractive index of air?
363
# P5 - Space for Reflection
They travel at different speeds in any given medium (but same in a vacuum).
Why are different colours of light refracted by different amounts?
364
# P5 - Space for Reflection
Red - refracted least and has lowest refractive index (1.514...)
Which colour of light slows down the least?
365
# P5 - Space for Reflection
Blue - higher refractive index (1.523...)
What colour of light is refracted most?
366
# P5 - Space for Reflection
A prism
What is used to make different colours of light emerge at different angles?
367
# P5 - Space for Reflection
Make different colours of white light refract, producing a spectrum - dispersion.
What can a prism do to light?
368
# P5 - Space for Reflection
When a spectrum is produced to show colours of rainbow.
What is dispersion?
369
# P5 - Space for Reflection
When light travels from a more dense medium with a higher RI to a less dense medium with a lower RI.
E.g. Glass to water
When does TIR only happen?
370
# P5 - Space for Reflection
When angle of incidence is greater than critical angle, ray of light won't come out but is reflected back into medium.
What is TIR?
371
# P5 - Space for Reflection
Most light passes through into air but little bit is internally reflected.
What happens when angle of incidence is less than critical angle?
372
# P5 - Space for Reflection
Emerging ray travels along the surface. Quite a bit internal reflection.
What happens when angle of incidence is equal to critical angle?
373
# P5 - Space for Reflection
No light comes out - all totally internally reflected
What happens when angle of incidence is greater than critical angle?
374
# P5 - Space for Reflection
The lower the critical angle will be.
Different media have different critical angles so the higher the refractive index of the medium....
375
# P5 - Space for Reflection
About 42º
What is the critical angle for glass?
376
# P5 - Space for Reflection
45º can be used to get TIR e.g. optical fibres
Why is a critical angle of 42 useful in glass?
377
# P5 - Space for Reflection
Optical fibres, prisms in binoculars, reflectors, road signs and cat's eyes.
What can TIR be used in?
378
# P5 - Space for Reflection
Where light rays from an object come together to form an image on a screen (inc. retina - eye's screen).
What is a real image?
379
# P5 - Space for Reflection
Project them onto a screen
What can you do to real images?
380
# P5 - Space for Reflection
When rays diverge so light from object appears to come from a different place.
What is a virtual image?
381
# P5 - Space for Reflection
Project it onto a screen
What can't you do with a virtual image?
382
# P5 - Space for Reflection
Virtual - object (face) appears behind mirror.
What type of image is looking in a mirror?
383
# P5 - Space for Reflection
Virtual - appears bigger and further away than it actually is.
What is the image when you look through a magnfiying glass?
384
# P5 - Space for Reflection
1. How big compared to original
2. Real or virtual
3. Upright or inverted
4. Where it is (in relation to lens and focal point)
What 4 things describe an image?
385
# P5 - Space for Reflection
Convex
What shape is a converging lens?
386
# P5 - Space for Reflection
Rays converge to a focus
What does a convex lens do to light?
387
# P5 - Space for Reflection
Focuses them at a point - focal point
What happens if the rays entering the lens are parallel to each other and to the principal axis?
388
# P5 - Space for Reflection
Distance between centre of lens and focal point
What is the focal length?
389
# P5 - Space for Reflection
Slows down upon entry and bends towards normal.
What happens to the speed of a ray travelling parallel to the principal axis?
390
# P5 - Space for Reflection
Speeds up - bends away from normal
What happens to a ray travelling parallel to the principal axis when it hits the 'glass to air' boundary?
391
# P5 - Space for Reflection
All the rays hitting different parts of lens are bent towards some focal point to form image.
When a ray is travelling parallel to the principal axis, what does the curvature of the lens mean?
392
# P5 - Space for Reflection
Pass straight through
What does a ray passing through the optical centre of the lens appear to do?
393
# P5 - Space for Reflection
At same angle as entry but on opposite side to principal axis, so bent same amount - opposite direction.
How does a ray passing through the optical centre of the lens exit?
394
# P5 - Space for Reflection
Turns diverging rays into parallel light
Describe how a convex lens can work in the opposite way...
395
# P5 - Space for Reflection
Real or virtual depending on how close object is to lens
What type of image can convex lenses produce?
396
# P5 - Space for Reflection
Real, inverted image, same size as object and at 2F
What will an object at 2F produce?
397
# P5 - Space for Reflection
Real, inverted image bigger than object and beyond 2F
What will an object between F and 2F produce?
398
# P5 - Space for Reflection
Virtual image, right way up, bigger than object and on same side of lens.
What will an object nearer than F produce?
