Flashcards in Unit 2 Deck (164):
What do waves do ?
They transfer energy from one point to another
What is a longitudinal wave ?
A wave in which the particles vibrate parallel to the direction the wave is travelling
Examples if longitudinal waves?
What are compressions ?
Places where the coils or particles bunch together
What are rarefactions ?
Places where the coils or particles are furthest apart
What is a transverse wave ?
One in which the particles vibrate at 90 degrees to the direction the wave is travelling
Examples of transverse waves
Water waves , electromagnetic waves
What is the frequency ?
The number of complete waves passing a fixed point in one second
What is wavelength ?
The distance between two consecutive crests or troughs
What is the amplitude ?
The greatest displacement of the wave from its undisturbed position
What can a ripple tank do?
It produces plane waves
What can the plane waves be used to study ?
Reflection and refraction
What does a hand-held stroboscope do?
Freezes the motionso that the wavelength measurements can be made
What happens when waves travel from deep water into shallow water ?
Waves slow down
Frequency stays the same
What law applies to wave reflection ?
Angle of incidence always equals the angle of reflection
What happens if the waves enter the shallow water at an angle ??
The angle of incidence in deep water is always greater than the angle of refraction
What is the range of human hearing ?
20Hz to 20000Hz
What is ultrasound?
Sounds above 20kHz which can't be heard by humans
How does sound travel ?
From particle to particle
Why can sound not travel through a vacuum ?
There are no particles
What is an echo?
A reflection of sound,ultrasound, microwaves or radio waves
What is sonar ?
Sound navigation and ranging
What is radar?
Radio detection and ranging
What are sonar and radar used for ?
They use echoes to locate a target and measure how far away it is
What does sonar use ultrasound for ?
E.g measuring size of baby's head in womb to the depth of s submarine below the surface- limited to fairly slow moving objects
What does radar use electromagnetic waves for ?
Used to locate very distant
Objects that may be moving very rapidly e.g a spacecraft leaving earths atmosphere
Ultrasound in industry ?
Cleaning sensitive electronic equipment
Scanning metal casings for faults or cracks
Ultrasound in medicine ?
Removing harmful tartar from teeth
Scanning a womb to check the development of the unborn child
What do all electromagnetic waves have in common ?
All travel in a vacuum
Travel at exactly the same speed in a vacuum
Are all transverse waves
Name the electromagnetic waves in order of increasing wavelength ?
Gamma - 0.01 nm
Visible light - 0.5 um
Microwaves - 3 cm
What can gamma waves be used for ?
Destroying viruses, killing cancer cells
What an x rays be used for ?
In medicine for diagnosis , to kill cancer cells
Why can UV rays be used for ?
Giving sun tans
Detect bank note forgeries
What can visible light be used for ?
What can IR rays be used for ?
Night vision goggles
What can microwaves be used for ?
What can radio waves be used for ?
Communication for entertainment
Dangers of each electromagnetic wave.
Gamma- can disrupt DNA
X-rays- disrupt DNA
UV- cause skin cancer
Visible light- cause snowblindness
IR- damages cells by burning
Microwaves - eye cataracts
Radio waves - no known dangers
Can people be in danger when standing next to communication masts or mobile phones ?
What is the precautionary principle ?
Children under the age of nine should use mobile phones sparingly
Use mobile phones with headphones
Mobile phone masts should not be erected near schools or hospitals
What does luminous mean ?
What does non-luminous mean ?
Light which has been reflected from luminous objects to our eyes
What are transparent materials ?
Let light travel readily ( air, water,glass)
What does opaque mean ?
Doesn't let light travel through
What is the law of reflection ?
Angle of incidence is always equal to the angle of reflection
Describe the image in a plane mirror ?
Same size as object
What is a virtual image ?
Images that can't be projected onto a screen
What are real images ?
Images that can be projected onto a screen
What happens when light slows down ?
It bends towards the normal
What happens when light speeds up ?
It bends away from the normal
What is dispersion ?
The breaking up of white light into its component colours
Why does red light refrsct the least ?
It is fasted in glass
Why does violet light refract the most ?
It is slowest in glass
What are endoscopes used for ?
To look inside a persons body without needing to cut a large hole
What is the principle focus ?
The principle focus is the Lindt a with the rays of light meet at a point
What is the focal length ?
The distance between the principle focus and the optical centre of a lens
Examples of good conductors ?
Silver , copper
Examples of semiconductors ?
Silicon and germanium
Examples of insulators ?
Plastic , rubber
Describe what static electricity is
When two insulators are rubbed together they both become electrically charged. This is because negatively charged electrons rub off one material in to the other . The material that gains electrons becomes negatively charged. The material loses electrons becomes positively charged
Do the electrons or the protons move ?
Describe what happens when a polythene rod is rubbed with a cloth .
Electrons are taken off the cloth( positively charged) and transferred to the polythene rod ( which is now negatively charged )
What is the law of static electricity ?
Opposite charged attract and same charges repel
What is polarisation ?
When a positively charged rod is brought near a tiny pice of aluminium in foil m the free electrons in the foil are pulled towards the rod creating a surplus of electrons at the top of the foil and a deficiency of electrons at the bottom of the foil
What are the dangers of static electricity?
What is a lightning conductor ?
A long ship of copper metal with a spike at the top running the length of the building and terminating the ground
Why do computer engineers wear earthed wrist straps ?
To reduce the possibility of destroying computer chips
Describe the flow of a conventional current ?
Positive to negative
Describe the flow of electrons ?
Negative to positive
What is the formula for charge ?
Q= current x time
How does an ammeter measure current in a circuit ?
Placed in series
How to measure the voltage across a component ?
Voltmeter in parallel
Formula for voltage ?
What is ohms law ?
The current through many conductors is directly proportional to the voltage across it provided the temperature remains constant
What is the formula for resistors in series ?
Rtotal = R1+ R2 + R3
What is the formula for resistors in parallel ?
1/Rtotal= 1/R1 + 1/R2 + 1/R3
Current in a series circuit ?
Current in every component in series is the same
Voltage in series current ?
Ass up to battery voltage
Voltage in parallel circuit?
Voltage across each component is quality go that of the battery
Current in parallel circuit?
Sum of currents = to current of battery
Formula for energy ?
E= Q xV
Formula for power ?
P= I2R or P= V2/R
Formula for power ?
What colour if the neutral wire ?
What is the colour of the live wire ?
What colour is the earth wire ?
Green and yellow striped
bLue goes ?
bRown goes ?
green and yellow sTriped goes ??
Average mains voltage ?
What is a solenoid ?
Wrapping the wire in the form of a long Steiger coil
How can the magnetic field strength be increased ?
Use a larger current
More turns of wire
Put a soft iron rod into the solenoid
How can't the turning effect be increased ?
Increasing the current in the coil
Increasing the strength of the magnetic field
Increasing the number of turns on the coil
What is the Big Bang theory ?
Occurred between 12-15 billion years ago started from a singularity, after the Big Bang the universe was made up of high energy radiation and elementary particles such as quarks. There was a period of rapid expansion. The expanding made the universe cooler,this allowed quarks to formtogethrr to produce protons and neutrons. Eventually the temperature fell low enough to allow electrons to combine with neutrons and protons to form atoms of hydrogen
Why is a sound that is approaching us have a higher pitch ?
Because it has a smaller wavelength
What happens when a sound is moving away from us ?
It has a lower pitch but bigger wavelength
What is blue-shifted ?
If the light we observe from a moving source has a shorter wavelength than expected it is because is is moving towards us
What is red shifted ?
If the light we observe has a longer wavelength than expected it is becuas the source is moving away form us
What is the absorption spectrum ?
There are black lines in the spectrum of light from the sun where hydrogen atoms have absorbed light
How do we know that the sun contains hydrogen ?
The absorption spectrum
What happens when we look at light from distant galaxies ?
We get the same pattern but it is shifted towards the red end of the spectrum - tells us the galaxies are moving away from us
What is CMBR?
Cosmic microwave background radiation
What is cosmic microwave background radiation ?
The remnant heat from the Big Bang ( echo)
What is the Big freeze ?
If there is too little mass the. The universe will continue expanding forever and get colder and colder and end in a big freeze
What is the Big Crunch ?
If there is enough mass in the universe the gpe forces will cause expansion to stop. Contraction will then start galaxies will move towards each other and collide and the universe will end in a Big Crunch
What is the Big Bounce ?
Gravity may be big enough to bring matter so close together that conditions will be similar to those after the Big. Bang. If further contraction occurs the universe may collapse to another singularity and another big band. Crunch Bang Crunch Bang
What is seti?
Search for extra terrestrial intelligence
What are the four problems with travelling to space ?
Flight time , engineering , logistics , ethical
What is the crust made out of ?
What is the mantle made out of ?
Silica and minerals of iron magnesium etc
What is the core made out of?
Iron and nickel
Describe the structure of the earth
Solid outer crust, thick viscous mantle, liquid outer core, dense solid inner core
What is the earths lithosphere?
The crust and the upper solid part of the upper mantle
Describe what happens when plates slide past each other
They catch on each other and as the pressure builds up they can suddenly lurch and cause an earthquake.
What happens when an oceanic and continental plate collide ?
Oceanic plate is less dense and is forced underneath the continental plate, as the oceanic crust is pushed down , friction caused the rocks to melt. The moltem rock is forced to the surface and volcanoes forms,there can also be earthquakes as the two plates slowly grind past each other. A deep trench formed on the ocean floor where th oceanic plate is being forced down. The continental courts crumples and Flores forming mountains along the coast
How to remember the order of the colours of dispersion ?
Tectonic plates due to magnetic field ?
Two tectonic plates move away from each other, magma fro mmantl is released onto ocean floor as lava . Iron particles in this lava are aligned with the earths magnetic field. As this lava solidifies, the direction in which these particles are pointing is frozen in to the rock Formed. The earths magnetic field reversed roughly once every 500,000 years. When this happens the iron particles in the lava which is deposited at the constructive plate boundary align themselves in the opposite direction to those which are deposited when the earths magnetic field has the opposite polarity,
Equation for time period ?
What happens when the angle of incidence is less than the critical angle?
Reflection and refraction occur
Wha is the image like that is formed from a concave diverging lens ?
Virtual diminished upright
How was the solar system formed ?
A nebula contracts due to the GPE force between its particles , as the nebula contracts it flattens into a disc and begins to rotate. A central mass forms -protostar
Rings form which later develop into planets
What is a star mainly made up of ?
What is accretion?
The clumping together of dust
Why is the solar system stable ?
Force of gravity which pulls inwards towards the centre , balances the outward force called radiation pressure
What is an electric current ?
A flow of electric charge
What is van de graaff?
Connected to earth via a sensitive ammeter , shows the flow of electric charge
Unit of charge ?
What is one coulomb made up of ?
6 million million million electrons
What does a diode do ?
Only allows current to foil in one durectipn
Method of finding how the voltage across a metal wire effects the current through it ?
Measure the current through the wired for 4 different voltage values
Is voltage directly proportional to current ?
What is resistance ?
The degree to which a component opposes the flow of electricity
How do you change mA to 1A ?
Divide by 1000
What does a diode do when it's forward-biased ?
Allows current to flow through
What does a diode do when it is reverse biased ?
It does not let current flow through it
Why is current measured in ?
What is resistance measured in ?
What affect does a thin wire have ?
Not much space, high resistance
What affect does a thick wire have ?
More space, low resistance
What happens when the length is a wire is increased ?
The resistance increases
What happens when the area of a wire is increased
The resistance decreases
What happens when the temperature is increased ?
The resistance increases
How do you use a distant object to measure the focal length of a converging lens ?
Tape a ruler to bench, place a white screen at 0 cm. then place lens in holder. Pick a distant object and slowly move lens away from white screen until the ibject is sharpest. Using a metre ruler measure the distance from the principal ficus to the centre of lens. Repeat thus experiment another 2 times to ensure the measurements are accurate
How are stars formed ?
Clouds of hydrogen and dust, particles of hydrogen come together because of gravity, these clouds become more and more dense as particles get close together, hydrogen particles start to spiral inwards and the temperature rises. 15million degrees Celsius. Nuclear fusion happens.
What does gravity do ?
New stars ,new galaxies , new planets
Evidence for the solar system being formed from a nebula ?
Planets orbit in same sense and same plane as the gas and dust clouds originally did
What are geostationary satellites used for ?
Telephone , to communications
What are low polar orbits used for ?
Taking photographs for weather forecasting
Describe the motion of geostationary satellites ?
Placed above equator and orbit the earth in the same direction as the earth spins on its axis
Motion of low polar satellites ??
Satellite sweeps over both poles while the earth rotates beneath it
Method for plotting field lines around a bar magnet ?
Place the magnet on a white sheet of paper, and draw its outline, place the plotting compass near the North Pole and with a pencil place a dot on the paper where the needle is pointing. Move compass so the dot is directly below the tail of the compass needle. Mark a new dot atvthechearcofvthe needle. Continue moving thr compass in this way jnilt you reach the magnet. Starting at diff points near the North Pole , repeat this procedure until several field lines have been drawn
What is the motor effect ?
A current carrying wire placed inside a magnetic field generally experiences a force. The direction is perpendicular to both the field lines and the current. Reversing th edirection of the current will reverse the direction of the force. The size of the force is greatest when the current is perpendicular to the field lines and zero when the current is parallel to the field lines
Flemings left hand rule ?
thuMb= movement, First finger = field, seCond finger = current
Current induction using two coils ?
When the switch is closed there is an increase in the current in the primary coil which induces a momentary current in the secondary coil. When a steady current flows in the primary coil there is no current in the secondary coil. As the switch Is opened there is a momentary current in the primary coil but this time in the opposite direction.
Formula for number of kWh ?
Number of kilowatts x number hours
Average frequency ?
What does the live wire do ?
Provides alternating voltage from mains
What does the earth wire do ?
Safety wire , normally a current does not flow in it, provides a low resistance path to earth in case of a fault
What is a fuse ?
The piece of wire that melts when a high curentfloes through it
Method for proving the law of reflection?
Draw a sharp line with a pencil and ruler on a sheet of white paper
Use a protractor to draw a normal
Draw straight lines at various angles to the normal ranging 15 - 75 degrees using a ruler
Place a plane mirror on the paper
Use a ray box and shine a ray of light along the line 15 degrees
Mark two crosses on the reflected ray
Measure angle of reflection
Repeat for diff angles
What happens when the angle of incidence is greater than the critical angle ?
Total internal reflection
Average critical angle for glass ?
Method for critical angle ?
Trace outline of semi circular glass block
Mark centre of straight edge
Direct ray at curved edge of block
Move ray / increase angle
Until refracted ray emerges along edge
Critical angle is between normal and incident ray