Flashcards in Physics Paper 1: Topics 1-6 Deck (93):
Equation for distance travelled for an object travelling at a constant speed
Distance travelled (m) = (average) speed (m/s) x time (s)
d = s x t
What is the speed of sound in air
What is acceleration, what is meant by uniform acceleration?
Acceleration is how quickly you’re speeding up (change in velocity over time) and uniform acceleration means constant acceleration
Equation for average acceleration
Acceleration (m/s^2) = (final velocity - initial velocity (m/s) ) / time (s)
a = (v-u)/t
What is acceleration due to gravity near earths surface
Equation for uniform acceleration.
Final velocity ^2 (m/s) - initial velocity ^2 = 2 x acceleration x distance
On a distance time graph, what does __ tell you:
- gradient at any point (if gradient curved, use a tangent)
- steeper gradient
- gradient at any point gives the speed of the object
- flat = object has stopped
- steeper graph, object travelling faster
- curves represent acceleration
- increasing gradient, object speeding up
- decreasing gradient, object slowing down
On a velocity time graph, what does __ tell you:
- gradient at any point (if gradient curved, use a tangent)
- steeper gradient
-straight line / and \
- area under graph
Flat section, steady speed
Steeper graph, greater acceleration or deceleration
Positive gradient, acceleration. Negative gradient, deceleration.
Curve, a changing acceleration
Straight line, / constant acceleration, \ constant deceleration
Area under graph, distance travelled in that time interval
What is Newton’s first law
Resultant force is needed to make something start moving, speed up or slow down, a non zero resultant force always produces acceleration in the direction of the force
What is Newton’s second law
Force and acceleration are directly proportional. Acceleration is inversely proportional to mass of an object.
Equation for resultant force
Resultant Force (N)= mass (kg) x acceleration (m/s^2)
F = m x a
What is equation for weight of an object
Weight (N) = mass (kg) x gravitational field strength (N/Kg)
W = m x g
G = 10 N/Kg on Earth
What is velocity?
Speed and direction of an object
What’s centripetal force?
Force that keeps something moving in a circle. Happens when object moving at constant speed is constantly changing direction, so constantly changing velocity, and so accelerating. Therefore must have a resultant force, which acts towards centre of circle
What’s Inertia? What’s an objects inertial mass?
Tendency for motion to remain unchanged (specifically velocity)
Inertial mass is how difficult it is to change the velocity of the object . The ratio of force over acceleration.
Equation for inertial mass
Inertial mass = force / acceleration
What’s Newton’s third law?
When two forces interact the forces they exert on each other are equal and opposite
Eg book on table: two normal contact forces against each other PLUS Weight due to gravity from Earth vs book pulling back up on Earth
Equation for momentum
Momentum (kg m/s) = mass (kg) x velocity (m/s)
P = m x v
How are changes in momentum caused?
When a resultant force acts on an object for a certain amount of time, it causes change in momentum
Equation for change in momentum
Force (N) = change in momentum (final momentum - initial momentum) (kg m/s) / time (s)
F = (mv-mu) / t
Equation for stopping distance
Stopping distance = thinking distance (affected by drivers reaction time and speed) + braking distance (affected by speed, conditions of breaks etc)
What are the eight energy stores
Kinetic, anything moving
Chemical, anything releasing energy through chemical reaction
Gravitational potential, anything in a gravitational field
Elastic potential, anything stretched
Electrostatic, two charges that attract or repel each other
Magnetic, two magnets
Nuclear, atomic nuclei release energy from this store in nuclear reactions
Equation for kinetic energy in an objects kinetic energy store
Kinetic energy (J) = 0.5x mass (kg) x (speed)^2 (m/s^2)
KE = 1/2 x m x v^2
Equation for change in gravitational potential energy in an objects gravitational potential energy stores
Change in gravitational potential energy (J)= mass (kg) x gravitational field strength (N/Kg) x change in vertical height (N/Kg)
Triangle GPE = m x g x triangle h
What are the four main ways of energy transfer between stores
Mechanically: force acting on object and doing work
Electrically: charge doing work against resistance
By heating: energy transferred from hotter to colder object
By radiation: energy transferred by waves
What does it mean when energy is dissipated
Energy is spread out and lost
What is the equation for total energy input
Total energy input = useful energy output + wasted energy
What’s the equation for the efficiency of a device?
Efficiency = useful energy transferred by device (J) / total energy supplied by device (J)
Times answer by 100 to get as a percentage
How does lubrication reduce unwanted energy transfers?
Reduces energy transferred by friction
Explain how conduction works
One side of object heats, particles vibrate more, collide with each other. Energy transferred from particles kinetic energy store to other particles, which then vibrate faster (energy transfers though the object)
What is thermal conductivity
How well a material transfers energy by conduction
What are bio fuels?
Renewable energy resources created from either plant products or animal dung
How does hydro electricity work?
Flooding valleys by building big dams, rain water caught and allowed out through turbines
How do tidal barrages work?
Big dams built across river estuaries with turbines in. Tide comes, fills estuary, water let our through turbines at a controlled speed.
What experiment do you use to investigate motion?
Trolley on ramp test
Can use this to test affect of Trolley’s mass and investigate effects of accelerating force
^ force and acceleration are proportional, mass and acceleration are inversely proportional
What experiment can be used to measure reaction time
Ruler drop experiment
Longer distance ruler falls = longer reaction time
What does a wave do?
I travels through a medium, causing particles in the medium to vibrate and transfer energy and information between each other. Overall, the particles stay in the same place,
What’s amplitude of a wave?
Displacement from rest position to a crest or a trough
What’s wavelength of a wave?
Length of a full cycle of a wave (eg from crest to crest)
What’s frequency of a wave
Number of complete cycles of a wave passing a certain point per second. Measured in Hertz, hz
1 hz = 1 wave per second
What’s the period of a wave
Number of seconds it takes for one full cycle
What’s equation to work out the period of a wave?
Period = 1/frequency
What’s a transverse wave?
Wave where vibrations are perpendicular (90*) to the direction the wave travels
(Vibrations up and down)
Eg: electromagnetic waves, waves in water, S-waves
What are longitudinal waves
Vibrations are parallel to direction wave travels
(Vibrations left to right)
Cause compressions in the mediums they pass through
Eg: sound waves, p-waves
What’s a compression and what’s a refraction?
Compressions are points where the wave is high pressure, with lots of particles
Rarefactions are points where the wave is low pressure, with fewer particles
What’s wave speed?
How quickly a wave moves through space
What are the two equations for wave speed?
Wave speed = frequency (Hz) x wavelength (m)
Wave speed (m/s) = distance (m) / time (s)
What is the experiment for measuring speed of sound waves
Use an oscilloscope to measure speed of sound
Attaching signal generator to speaker allows you to generate sound at a specific frequency. Use two microphones and an oscilloscope to find the wavelength of the sounds generated.
What is the experiment for measuring speed of water waves
Measure speed of water ripples using a strobe light. Use signal generator attached to dipper of ripple tank to create water waves at a set frequency. Frequency of strobe lights and waves are same when waves appear to stop moving.
What is the experiment for measuring speed of waves in solids
Use peak frequency
Measure frequency of sound waves produced when you hit the object, sound waves produced around object have same frequency as waves produced in the object
What’s a material interface?
What three things can happen when a wave meets a material interface
A boundary between two materials
- wave absorbed by second material
- wave transmitted through second material (carries on travelling through)
- wave reflected, incoming ray sent back away from second material
Wave hits boundary at an angle, the change of speed between materials due to different densities of materials causes a change in direction of wave
- slows down, bends towards normal
EM waves tend to slow down in denser materials
On a ray diagram what is:
- the normal
- the angle of incidence
- angle of refraction
- how are the ‘rays’ shown
- normal, imaginary line perpendicular to the point incoming wave hits boundary
- incidence, angle between incoming (incident) ray and normal
- refraction, angle between refracted ray and normal
- rays are shown as straight lines perpendicular to the wave fronts
What’s the experiment to investigate refraction
Use transparent materials. Use a ray box to produce thin ray of visible light to be refracted
What are electromagnetic waves?
Transverse waves. Vibrations of electric and magnetic fields, can travel through a vacuum. Generated by a variety of changes in atoms in their nuclei, therefore have a large range of frequencies
EM waves transfer energy from a source to an absorber. Higher frequency > greater energy transferred
List the EM spectrum. Which end has longest wavelengths? Which end has highest frequency? Which ones are ionising radiation? Which ones cause heating?
Radio waves (long wavelengths, low frequency)
Microwaves (cause heating)
Infrared (cause heating)
Ultra violet (ionising - cause mutations)
Gamma rays (ionising) (short wavelength, high frequency)
Describe how EM waves are produced
EM waves are made of oscillating electric and magnetic fields. Alternating currents are made up of oscillating charges, so when charges oscillate they produce EM waves with the same frequency as the alternating current.
What’s a transmitter?
Object in which charges (electrons) oscillate to produce radio waves
How are microwaves used?
For communication, they’re passed through earth’s watery atmosphere
For microwave ovens, they are absorbed by water molecules in food
How is Infrared radiation produced and how’s it used?
All hot objects give out IR radiation. Hotter object, more IR.
Thermal imaging: infrared cameras detect IR, turns it into electric signal, which is displayed on a screen as a picture
IR can transfer information eg in phones/tv remotes
What’s a use of visible light
Photographic film reacts to visible light and films an image
Digital camera contains image sensors, detects visible light, generates electrical signal, converts into image
What’s a use of ultraviolet
Used in fluorescent lamps. Fluorescent chemicals absorb UV, emit visible light
What’s a use of X-rays
Make image show up on photographic film
Radiographers take X-ray images: X-rays transmitted by flesh, absorbed by denser material eg bone. Create negative image.
Used in airport security scanners to detect hidden objects
What’s a use of gamma rays
Used for sterilisation, kill microbes
Used in cancer treatment
Some medical imaging techniques use gamma to detect cancer
What’s guess of overall size of an atom
(Sizes for atoms always written in negative form)
What do atoms form?
Atoms join together to form molecules
Relative mass and relative charge of proton, neutron and electron?
Proton: mass 1, charge +1
Neutron: mass 1, relative charge 0
Electron: mass 0.0005, charge - 1
What’s ionising radiation?
Any radiation that can knock an electron from an atom by absorbing the radiation, which has enough energy to move the atom out all the electron shells
What’s the atomic number tell you?
The number of protons
What’s the mass (nucleon) number tell you.?
Number of protons + neutrons
If an element is written as ‘carbon-14’ what does the 14 mean?
14 is the mass number, has 14 protons + neutrons
What’s an isotope.
isotopes of an element are atoms with the same atomic number but a different mass number. All elements have multiple isotopes, usually only a few are stable.
What’s radioactive decay?
Where unstable isotopes decay into other elements and give out radiation as they try to become more stable.
Radioactive substances emit one or more type of ionising radiation during decay
Summarise alpha radiation
An alpha particle emitted from a nucleus. Alpha particle has 2 neutrons and 2 protons (like a helium nucleus)
They don’t penetrate far and are stopped quickly. Can travel a few cm in air, absorbed by a thin sheet of paper. Are strongly ionising (due to their size)
Summarise beta radiation
Beta particles can be electrons or positrons
B- particle is a fast moving electron released by nucleus. Have virtually no mass and a relative charge of -1
B+ particle is a fast moving positron (same mass as electron, +1 charge)
Both are moderately ionising. B- move a few meters in air, absorbed by 5mm thick aluminium sheet. B+ has a smaller range
When a positron hits and electron, the two destroy each other and produce gamma rays
Summarise gamma rays
Nucleus decayed, undergoes nuclear rearrangement and releases some energy. Gamma rays are waves of EM Radiation released by nucleus. They carry away this released energy.
Travel for a long distance in air. Penetrate far into materials. Absorbed by thick lead sheets or metres of concrete. Weakly ionising as usually pass through rather than collide with atoms
What do nuclear equations do? How are they structured
They show the radioactive decay by using element symbols. Total mass and atomic numbers must be equal on both sides
Atom before decay > atom after decay + radiation emitted
What does alpha decay do to an atom in a nuclear equation?
Mass number decreases by 4, atomic number decreases by 2
What does beta minus decay do to an atom in a nuclear equation?
Mass number doesn’t change, atomic number +1
What does positron emission do to an atom in a nuclear equation?
Mass number doesn’t change, atomic number -1
In alpha and beta emissions, new element formed due to change in atomic number
What does neutron emission do to an atom in a nuclear equation?
Mass number -1, atomic number stays the same
What does gamma emission do to an atom in a nuclear equation?
Mass and atomic numbers stay the same
What are radioactive sources?
Contain radioactive isotopes which give out radiation from nucleus of atoms. This is a random process
What’s activity (in radiation)
Rate at which the source decays. Measured in Becquerels, Bq.
1 Bq = 1 decay a second
Radioactive nucleus decay one by one, this activity never reaches zero
What two items can be used to measure activity of a radioactive source
A Geiger Müller Tube: clicks every time it detects radiation. Can attach it to a counter
Photographic film: more radiation > film gets darker
What’s half life?
The average time taken for number of radioactive nuclei in isotope to halve
Short half life > activity falls quickly > nuclei very unstable, rapidly decay
^ very dangerous at start, quickly becomes safe
How do you plot a graph to show radioactive activity, How do you find half life on this graph
Plot graph of activity against time (take into account background radiation)
Half life = time interval on bottom axis corresponding to a halving of activity on a vertical axis
What’s background radiation?
Low level radiation that’s around us all the time. Comes from radioactivity of naturally occurring unstable isotopes, eg air, food, rocks
What are cosmic rays?
Radiation from space. Mostly comes from the sun. Earths atmosphere protects us from most of this
What’s the ‘absorbed radiation dose’ mean?
The amount of radiation you’re exposed to (amount of energy your body absorbs)
Varies depending on where you live
What does it mean if something’s irradiated
Object exposed to radioactive source (humans are always irradiated by BR)
Irradiation = outside body