EOY Exams Flashcards
weight
mass x gravitational field strength
work done
force × distance (parallel to the force)
force applied to a spring
spring constant x extension
moment of a force
force x distance (perpendicular to object)
pressure
force normal to a surface/area of surface
distance travelled
speed × time
acceleration
change in velocity/time taken
resultant force
mass x acceleration
momentum
mass x velocity
kinetic energy
0.5 x mass × (speed)^2
gravitational potential energy
mass x gravitational field strength x height
power
energy transferred or work done / time taken
efficiency (energy)
useful output energy transfer/total input energy transfer
efficiency (power)
useful power output / total power input
wave speed
frequency × wavelength
density
mass/volume
Law of conservation of energy
energy cannot be created or destroyed
gpe > ke > heat and sound (on hitting the ground)
Energy transfers for a falling object
chemical > electrical > light and thermal
Energy transfers in a torch
chemical
The energy store in a battery
elastic potential energy
The energy store in a stretched bungee rope
Work is done by brake pads to overcome friction causing what energy transfer?
ke > thermal energy
m x g x h
equation for GPE
equation for EPE
1/2 x spring constant x extension ^2
useful energy
energy that is transferred to where it is wanted in the way that it is wanted
energy that is dissipated
energy that is wasted and spreads out into the surroundings, normally as heat energy
efficiency
the proportion of energy that gets transferred usefully
100%
the maximum efficiency possible when no energy is wasted
Ways to improve energy efficiency
lubrication, streamlining, low electrical resistance, reduce vibrations
Power
the rate of energy transfer (how quickly energy is changed into other forms)
Biofuel
any fuel taken from (recently) living organisms, e.g. wood, manure
renewable
a fuel that can be replaced as quickly as it used
carbon-neutral
the CO2 released into the atmosphere when it burns is equal to the energy removed from the atmosphere as the living organism was growing
Uranium or plutonium
nuclear fuels
unreliable as it’s not always windy so cant continually produce electricity
disadvantage of wind power
Solar cells
convert energy from the sun directly into electricity
solar heating panels
absorb energy from the sun to heat up water
geothermal energy
energy taken from hot rocks underground
disadvantage of nuclear power
radioactive waste is produced
fossil fuels
coal, gas, oil
non-renewable fuels
coal, gas, oil, nuclear
Carbon dioxide
the gas released when fuels are burnt that contributes to the greenhouse effect
What does energy transfer by conduction through a material depend on?
- Its thermal conductivity
- Greater thermal conductivity = More energy per second transferred
What do good insulators need?
Low thermal conductivity so that energy transfer through them is as low as possible
The energy transfer p/s through a layer of insulating material depends on
- The temp. DIFFERENCE across the material
- The THICKNESS of the material
- the thermal CONDUCTIVITY of the material
To reduce the energy transfer as much as possible
- Thermal conduc. of the insulating material should be as LOW as possible
- The thickness of the insulating material should be as THICK as possible
Temperature rise depends on
- The amount of energy supplied to it
- Mass of the substance
- What the substance is
Specific heat capacity
- The energy needed to raise the temperature of 1kg of the substance by 1ºC
Energy transferred (joules) (in terms of SHC)
= Mass (kg) x Specific Heat Cap (J/kgC) x Temperature change (C)
Loft insulation
- Fibreglass reduces the rate through the roof
- The air between the fibres also helps to reduce the rate by CONDUCTION
- Greater number of layers of insulation = Thicker insulation
Cavity wall insulation
- Reduces the rate through the outer walls of the house
- Space between the two layers of brick that make up the wall
- Ventilation is pumped into the cavity and air is trapped into small pockets (CONDUCTION)
Aluminium foil
- Between a radiator panel and the wall REFLECTS radiation away from the wall
- Reduces the rate by RADIATION
Double-glazed windows
- Two glass panes with dry air or a vacuum between the panes
- Thicker glass = lower thermal conductivity = slower rate by CONDUCTION
External walls
- Thicker bricks and lower thermal conductivity = lower rate inside to the outside = cost of heating is lower
Solar panels
- Absorb infrared radiation from the sun
- Generate electricity directly (solar panel cells) or heat water directly (solar heating panels)
- In the northern hemisphere, it is fitted on a roof that faces SOUTH
Infrared radiation
Electromagnetic waves with wavelengths that are longer than visible light but shorter than microwaves around 700-1000nm
Properties of Dark, Matte surfaces
-Good emitters and absorbers of infrared radiation
-Transfer energy and cool down more quickly than the same surface painted shiny white
process of conduction in a metal
When metals are heated their free electrons gain kinetic energy and move through the metal, transferring energy by colliding with other particles.
process of conduction in a solid (non metal)
Particles gain kinetic energy when heated and vibrate more. This energy is passed to neighbouring particles and so energy is transferred through the solid
Evaporation
The change of a substance from a liquid to a gas- Evaporation takes place because the most energetic liquid molecules escape from the liquid’s surface and enter the air.
Why does evaporation cause cooling?
The most energetic liquid molecules escape from the liquids surface into the air and so the average kinetic energy of the remaining molecules is less. This causes the temperature of the liquid to decrease.
Ways to maximise the rate of energy transfer to keep things cool
To do this we may use things that
-Are good conductors
-Are painted dull black
-Have the air flow around them maximised
Ways to minimise the rate of energy transfer to keep things warm
To do this we may use things that
-Are good insulators
-Are white and shiny
-Prevent convection currents by trapping air in small pockets
The U-Value
Tells us how much energy per second passes through a material. The lower the U-value the better the material is as an insulator
power
Energy transferred / time
units of power
watts
equation linking mass, energy, change in temperature and specific heat capacity
𝐸=𝑚𝑐Δ𝜃
heat absorption
heat enters an object
emit
to give off
What are renewable energy sources?
energy sources that will never run out but, they don’t provide as much energy and some are unreliable
Give 5 examples of renewable energy sources
bio-fuels
wind
the sun
hydro-electricity
tides
How are fossil fuels obtained?
Fossil fuels are natural resources that form underground over millions of years that are, typically, brunt to provide energy
What are the three main fossil fuels?
coal oil and natural gas
What are the pros of fossil fuels?
They are reliable(there are lots of fossil fuels)
The cost of extracting and building fossil fuel power plants are cheap
What are the pros of nuclear power?
It is reliable and although nuclear power plants are costly to build, they are safe to decomposition
What are the cons of fossil fuels?
1)They create environmental problems because they release carbon dioxide into the air which contributes to the greenhouse effect and global warming.
2)oil spillages affect animals that live near and in the sea.
3)Burning coal and oil can release sulfur dioxide which causes acid rain
What are the cons of nuclear power?
it is clean but disposing waste products is expensive and difficult. There is always a risk of a disaster.
What are bio-fuels?
They are created from plant or animal products and can be burnt to produce electricity
What is a feature of bio-fuels that links to carbon?
bio fuels are carbon neutral because plants are planted at the same rate that they are burnt
Why are bio fuels fairly reliable?
they take a relatively short time to grow and can be grown at any time so they respond to immediate energy demands
What is a con of bio fuels?
The cost of them are very high because space and water is used to grow plants that are needed for food
How does some of the production of bio-fuels increase methane and carbon dioxide emission?
deforestation has occurred which increased methane and carbon dioxide emission as well as killing the habitats of animals
How do wind turbines produce electricity?
the wind power rotates the blades which produces electricity, there is no pollution
How much (roughly) are wind turbines?
the initial costs are quite high but the running costs are minimal
What are 4 disadvantages of wind turbines?
1)lots are needed to produce a substantial amount of power
2)they are noisy
3)they can spoil the view
4)they only work when it is windy so they cannot supply high demand electricity
How do solar panels work?
They are made from materials that use energy transferred by light to create an electric current
Where and what kind of objects are solar power usually used in?
remote places like road signs and satellites and only on a small scale like in homes
Does solar power cause pollution?
no
What are the costs of solar power like?
the initial costs are high but they have no running costs
What is disadvantage of solar power?
it is weather dependent because the sun is needed and solar power cannot be produced at dark times e.g at night
How is hydro electricity produced?
A valley is flooded with a big dam the rain water is caught and allowed out through turbines
Does hydro electricity produce pollution?
no
Why does hydro electricity impact the environment?
When the valley is flooded, habitats of species are damaged
What is a big advantage of hydro electricity?
it can immediately respond to increased electricity demand because more water can be let through the turbines to generate more electricity
what are the costs of hydroelectricity like? reliability?
the initial costs are high but there are minimal running costs and it is a reliable energy source
What are tidal barrages?
tidal barrages are big dams built across river estuaries with turbines in them
How do tidal barrages produce electricity?
As the tide comes in it fills up the estuary .The water is then let out through turbines at a controlled speed to generate electricity
What are 3 disadvantages of tidal barrages
1)they affect boat access
2)they can spoil the view
3)they alter the habitat for wildlife
How reliable are tidal barrages?
Tides occur twice a day so they are quite reliable but the height of the tide is a variable because barrages don’t work when the water level is the same on either side
what are the costs of tidal barrages?
initial costs are moderately high but there are no fuel costs and there are minimal running costs
Objects that have a _____ density than water will float in water
Lower
What is the density of water in kg/m^3?
1000
The particles of a solid are held next to each other in _____ positions
Fixed
Which state of matter cannot flow?
Solid
What state of matter has a fixed shape and volume?
Solid
Which state of matter is the least energetic?
Solid
The particles of a ______ move about randomly and are in contact with each other
Liquid
Which state of matter can flow, fits it’s containers shape, and has a fixed volume?
Liquid
The particles of a ___ move randomly and are far apart from each other
Gas
Which state of matter can flow, fills its container, and does not have a fixed volume?
Gas
Which state of matter is the most energetic?
Gas
When a substance changes state its ____ stays the same because the number of particles stay the same
Mass
While a substance changes state, its ___________ stays the same
Temperature
The ____ section of temperature-time graph gives the temperature of a state change
Flat
What is the change of state from a liquid to a gas known as?
Evaporation
What is the change of state from a solid to a liquid known as?
Melting
What is the change of state from a liquid to a solid known as?
Solidifying
What is the change of state from a gas to a liquid known as?
Condensing
What is the change of state from a solid to a gas known as?
Sublimation
What is the change of state from a gas to a solid known as?
Deposition
The total kinetic and potential energy stored by the particles of a substance
Internal energy
The amount of energy needed to change the state of 1kg of a substance at the temperature at which it changes state (without changing temperature)
Specific latent heat
Specific latent heat of ______ involves a substance changing from a solid to a liquid
Fusion
Specific latent heat of ____________ involves a substance changing from a liquid to a gas/vapour
Vaporisation
Specific latent heat = Energy / ?
Mass
The specific latent heat of water can be measured using a low-voltage ______ to heat the water
Heater
___ ________ is caused by the random impacts of gas molecules on surfaces that are in contact with the gas
Gas pressure
Increasing temperature increases gas pressure because energy is transferred to the gas, increasing the _______ energy of its particles and resulting in more collisions
Kinetic
Increasing temperature increases gas pressure because the particles move faster so they hit the surfaces with a _______ _____
Higher force
Increasing temperature increases gas pressure because the number of impacts per second of particles increases, so the _____ _____ of the impacts increases
Total force
The unpredictable motion of smoke particles is evidence of the ______ motion of gas particles
Random
For a fixed mass of gas at a constant temperature, its pressure is increased if its ______ is decreased
Volume
For a fixed mass of gas at a constant temperature, reducing the volume of the gas _________ the number of particle impacts per second
Increases
The temperature of a gas can ________ if it is compressed rapidly because work is done on it and the energy isn’t transferred quickly enough to its surroundings
Increase
Boyle’s Law- Pressure x Volume is
Constant
The temperature of a gas is related to the average _______ energy of the particles
Kinetic
displacement
distance in a given direction
driving force
driving force
force of a vehicle that makes it move (sometimes referred to as motive force)
effort
the force applied to a device used to raise a weight or move an object
force multiplier
a lever used so that a weight or force can be moved by a smaller force
forces
(measured in newtons, N) can change the motion of an object
free-body force diagram
a diagram that shows the forces acting on an object without any other objects or forces shown
friction
the force opposing the relative motion of two solid surfaces in contact
load
the weight of an object raised by a device used to lift the object, or the force applied by a device when it is used to shift an object
magnitude
the size or amount of a physical quantity
moment
the turning effect of a force defined by the equation: moment of a force (in newton metres, Nm) = force (in newtons, N) x perpendicular distance from the pivot to the line of action of the force (in metres, m)
Newton’s first law of motion
if the resultant force on an object is zero, the object stays at rest if it is stationary, or it keeps moving with the same speed in the same direction
Newton’s second law of motion
F=ma
Newton’s third law of motion
when two objects interact with each other, they exert equal and opposite forces on each other
parallelogram of forces
a geometrical method used to find the resultant of two forces that do not act along the same line(draw parallelogram with force = distance (5 N = 5 cm) and make a parallelogram with distances and angles equal
principle of moments
for an object in equilibrium, the sum of all the clockwise moments about any point = the sum of all the anti-clockwise moments about that point
resultant force
a single force that has the same effect as all the forces acting on the object
acceleration
The rate of change of velocity (in metres per second per second, m/s²).
deceleration
The rate of change of velocity when an object slows down.
displacement
Distance in a given direction.
tangent
A straight line drawn to touch a point on a curve so it has the same gradient as the curve at that point.
velocity
Speed in a given direction (in metres per second, m/s).
distance-time graph
The gradient of this kind of graph represents the speed of an object.
vector
A physical quantity that has direction as well as magnitude. e.g. velocity.
scalar
A physical quantity that has magnitude, but not direction. e.g. speed.
velocity-time graph
The gradient of this kind of graph represents the acceleration of an object. The area under the line represents the distance traveled.
Directly proportional
A graph will show this if the line of best fit is a straight line through the origin
Driving force
Force of a vehicle that makes it move (sometimes called motive force)
Elastic
Able to regain its shape after it has been stretched or squashed
Extension
The increase in length of a spring, or strip of material, from its original length
Force multiplier
A lever used so the output force can be larger than the input
Free body force diagram
Illustration showing all the forces acting on an object, with no other forces shown
Friction
The force opposing the relative motion of two solid surfaces in contact
Hooke’s Law
The extension of a spring is directly proportional to the force applied, as long as its limit of proportionality is not exceeded
Inertia
The tendency of an object to stay at rest or to continue in uniform motion
Limit of proportionality
Beyond this point, Hooke’s Law does not apply
Magnitude
The size or amount of a physical quantity
Newton’s First Law of Motion
If the resultant force on an object is zero, the object stays at rest if it is stationary, or keeps moving with the same speed in the same direction
Newton’s Second Law of motion
The acceleration of an object is proportional to the resultant force on the object and inversely proportional to its mass
Newton’s Third Law
When two objects interact with each other they exert equal and opposite forces on each other
Resistive forces
Forces such as friction and resistance that oppose motion of an object
Spring constant
Force per unit extension of a spring (number of newtons needed to stretch a spring by an extra 1m)
What is a fluid?
liquid or gas
direction of pressure on a surface in a liquid
90°
State the equation that links area, force and pressure
F = P x A
What are the units of pressure?
Pa or N/m²
What is this equation used to calculate?
p=height of column x density x gravity
The pressure due to a fluid at a depth, h, below the surface of the liqiud
What is the effect of increasing density, depth or gravity on the pressure in a fluid
pressure increases
Explain why pressure increases with depth
The height of the column of fluid above the point increases so the weight of the fluid in the column increases.
P=F/A so if F increases (remember weight = force), P also increases.
How would you calculate the pressure difference between 2 points in a fluid?
difference in pressure = difference in depth x density x gravity
(only if we can assume density is constant)
Define upthrust
The resultant force on an object due to the difference in pressure between the top and bottom surfaces.
Explain why an object would float
It has a density lower than the density of the fluid it is in
so Upthrust > weight of object
Explain why and objects would sink
It has a density higher than the density of the fluid it is in
so Upthrust < weight of object
How to calculate the upthrust on an object
Upthrust = the weight of the fluid displaced by the object
(=volume of object x density of fluid x g)
Describe the pressure along a horizontal line in a fluid
Pressure is constant as there is the same depth hence weight of fluid above each point
Water leaving holes in the side of a bottle
Water pressure is greater at greater depths so water will leave a lower hole at a greater acceleration and travel a greater distance
1m² =
10000cm² (100 x 100)
Change in atmospheric pressure with altitude
At higher altitudes, pressure decreases because the number of air molecules (the weight of air) above that point is less (as height of the column of air above that point and the density have decreased)
What is the atmosphere?
A thin layer of air all round the Earth
What creates atmospheric pressure?
Air molecules colliding with a surface
Acts equally in all directions
Direction of pressure in a fluid (liquid or gas)
Amplitude
The height of the wave crest or the depth of the wave trough from the position at rest
Wavelength
The distance from one crest to the next crest, or from one trough to the next trough
Frequency
The number of wave crests passing a point in one second
Speed =
Frequency x wavelength
Period =
1 / frequency
Hertz
Unit of frequency
Wavelength of longitudinal wave
Distance from the middle of one compression to the middle of the next.
Frequency of longitudinal wave
The number of compressions passing a point in second
We use waves for
Transferring energy and information
Oscillation
Vibration
Oscillation of a transverse wave
Is perpendicular to the direction of travel
Oscillation of a longitudinal wave is
Parallel to the direction of travel
Make up of a longitudinal wave
Compressions and rarefactions (molecules get closer together and further away respectively)
Electromagnetic waves are all
Transverse waves
Mechanical waves are
Transverse or Longitudinal
Mechanical waves need
A medium to travel through (e.g. string, spring, sound waves)
Refraction
When a wave crosses the boundary between two substances and changes speed and direction
Reflection
Waves in a ripple tank meet an obstacle and bounce away at the same angle
What is the speed of all electromagnetic waves?
300,000,000 m/s
What is the relationship between energy and frequency?
The higher the frequency of a wave, the more energy it transfers
Why is light from lamps and the sun called ‘white light’?
It contains all the colours of the visible spectrum
How does the wavelength change from violet to red?
It increases
How does a film camera work?
The light is focused by the camera lens onto a light sensitive film. The film then needs to be developed to see the image of the object that was photographed
How does a digital/mobile phone camera work?
The light is focused by the lens onto a sensor which is made up of thousands of tiny light-sensitive cells called pixels. Each pixel gives a dot of the image and the image can be seen on a small screen at the back of the camera. When a photograph is taken, the image is stored electronically on a small memory card
How does temperature affect infrared radiation emitted?
The hotter an object, the more infrared radiation it emits
Why do optical fibres use infrared radiation instead of light?
Infrared is absorbed less than visible light in the glass fibres
How do TV remote controls use infrared radiation?
When you press a button on the handset, it sends out a series of infrared pulses. Infrared radiation is used because infrared pulses can be produced and detected electronically
How can infrared be used in medicine?
It can be used in scanners to show particularly hot areas of the body emitting more infrared which could indicate unhealthy tissue
How can infrared radiation be used to monitor temperature?
Hotter objects emit more infrared radiation than cooler objects, so an infrared camera allows you to see which objects are emitting more infrared radiation
How can infrared radiation be used to heat up objects (food) quickly?
Electric heaters contain long wires which heat up easily. These then emit infrared radiation and heat up the room quickly. Electric hobs heat up food faster than normal hobs because halogen hobs are designed to emit much more infrared radiation than normal ones
How are microwaves used for communication?
Microwaves can pass through the atmosphere so they can reach satellites above the earth and so can be used for TV signals. They also carry mobile phone signals
How are microwaves used for heating?
Microwaves penetrate into food and are absorbed by the water molecules, heating up the food. They heat food faster than ordinary ovens
What are radio waves used for?
To carry TV, radio and mobile signals. You can use them instead of cables to connect a computer to a mouse or printer, e.g via Bluetooth
Why can radio and microwaves be dangerous?
They can penetrate into the body, potentially heating up tissues
How can infrared radiation be dangerous?
It can cause burns and skin damage
What features do shorter wavelength radio waves have?
- the more information they carry
- the shorter their range (absorbed by the atmosphere)
- the less they spread out
Why are microwaves used instead of radio waves for satellite communication?
- they can travel between earth and space as they can penetrate the watery atmosphere
- they have a longer range so the signal doesn’t weaken as much
Why do scientists think mobile phone use should be limited?
They emit EM radiation which can be damaging especially to younger children with thinner skulls
How do radios receive a signal?
- an oscillator supplies carrier waves in the form of an alternating current
- the audio signal is supplied to the transmitter where it’s used to modulate the carrier waves
- the modulated carrier waves are supplied to the aerial. The varying alternating current causes it to emit radio waves that carry the audio signal
- when they are absorbed by a receiver aerial, they induce an alternating current, which causes oscillations
- the receiver circuit separates the audio signal from the carrier waves which is then sent to a loudspeaker
What are optical fibres?
Very thin glass fibres used to transmit information as infrared or visible light
How do optical fibres compare to radio waves or microwaves?
- they carry much more information as light has a shorter wavelength than radio waves
- they are more secure as the signals stay in the fibre
Give two uses of UV light
- security marker signs are used in security - they emit visible light in ultraviolet light
- energy efficient lightbulbs - they absorb UV light and emit visible light
How are UV rays harmful to humans?
They can damage the eyes and cause blindness. They can also change the DNA of skin cells and cause skin cancer
Why do x-rays and gamma rays have similar properties?
- they are at the short-wavelength end of the EM spectrum
- they carry much more energy per second than longer-wavelength EM waves
How do x-rays differ from gamma rays?
X-rays are produced when particles moving at high speeds like electrons are stopped - x-ray tubes are used to produce x-rays. On the other hand, gamma rays are produced by radioactive substances when unstable nuclei release energy. Gamma rays also have shorter wavelengths, so can penetrate further into substances than x-rays
How can gamma rays be used to kill bacteria?
Exposing food to gamma rays kills 99% of disease-carrying organisms. It can also be used to sterilise surgical equipment and prevent infection spreading in hospitals
How can gamma rays be used to kill cancer cells?
A narrow beam of gamma rays from a radioactive source like cobalt-60 is fired directly at the tumour. The beam is aimed at it from different directions to kill the tumour but not the surrounding tissue
What happens if a living cell becomes ionised?
It can damage or kill the cell and cause cancer. High doses kill cells, and low doses cause gene mutation and uncontrolled growth
Why must people who work with ionising substances wear a film badge?
If this badge shows that it is over-exposed to ionising radiation, its wearer is not allowed to continue working with the equipment for a period of time
Which types of tissue absorb x-rays and which do they pass through?
They pass through soft tissues but are absorbed by harder areas like bones and teeth
Why does a radiograph show a ‘negative image’ of a bone?
The parts of the film or detector that the x-rays reach appear darker than the other parts. So the bones, which absorb x-rays, appear lighter than the surrounding tissue
What does a contrast medium do?
It allows internal surfaces in the organ to be seen on the radiograph. The medium absorbs x-rays easily and so any organ consisting of soft tissue is filled with a contrast medium. For example, to obtain a stomach x-ray, the patient is given a barium meal before the x-ray as barium is a good absorber of x-rays
Why are there lead plates between the patient and the tube?
They stop x-rays reaching other parts of the body. The x-rays reaching the patient pass through a gap between the lead plates
What is a flat panel detector?
A small screen that contains a charged couple device (CCD). The sensors in the CCD convert x-rays to light which create electronic signals in the sensors which are then sent to a computer to produce an image
What is radiation dose?
A measure of the damage done to their body as a result of exposure to ionising radiation
Give three factors affecting radiation dose
- the time exposed for
- the type of radiation used
- the energy per second absorbed from the radiation
How do x-rays used for imaging differ from x-rays used for treating cancer?
X-rays used for imaging carry much less energy than those for therapy. Low energy x-rays are suitable for imaging as they are absorbed by bones and teeth and pass through body tissues or gaps like cracks in bones. Low energy x-rays don’t contain enough energy to destroy tumours
Angle of incidence
Angle between the incident ray and the normal
Angle of reflection
Angle between the reflected ray and the normal
Concave lens
A lens that makes parallel rays diverge (spread out)
Converging lens
A lens that makes parallel light rays meet, sometimes also known as a convex lens
Diffuse reflection
Reflection from a rough surface - the light rays are scattered in different directions
Dispersion
The splitting of white light into the colours of the spectrum
Diverging lens
A lens that makes light rays parallel to the axis spread out, also known as a concave lens
Focal length
The distance from the centre of a lens to the point where the light rays parallel to the principal axis are focused (or, in the case of a diverging lens, appear to diverge from)
Magnifying glass
Converging lens used to make a large image of a small object, which is placed between the lens and its focal point
Normal
Straight line through a surface or boundary perpendicular to the surface boundary
Opaque
Light cannot pass through
Oscillate
Move to and fro about a certain position along a line
Perpendicular
At right angles to
Specular reflection
Each light ray bounces off a smooth surface in a single direction
Total internal reflection
What happens when light hits a boundary between two transparent materials and all of it bounces back
Translucent
Allows light to pass through but the light is scattered or reflected
Transmission
When a wave passes through a substance
Transparent
Transmits all incident light
Transverse wave
A wave whose vibration is perpendicular to the direction of energy transfer (the wave direction)
Vibrate
Oscillate (move to and fro) rapidly about a certain position
Virtual image
An image seen in a lens or mirror that can’t be projected on a screen
Wave speed
Distance travelled per second by a wave crest or trough, measured in m/s
Wavelength
The distance from one wave crest to the next
White light
Light made of all the colours of the spectrum
Big Bang theory
The theory that the universe was created in a massive explosion and has been expanding ever since
Black body radiation
The radiation emitted by a perfect black body (a body that absorbs all the radiation that hits it)
Black dwarf
A star that has faded out and gone cold
Black hole
An object in space that has so much mass that nothing, not even light, can escape from its gravitational field
Centripetal force
The resultant force towards the centre acting on an object moving in a circular path
Cosmic microwave background radiation
Electromagnetic radiation that has been travelling through space ever since it was created shortly after the Big Bang
Dark matter
Matter in a galaxy that cannot be seen (its presence is deduced because galaxies would spin much faster if their stars were their only matter)
Main sequence
Life stage of a star during which it radiates energy due to fusion of hydrogen nuclei in its core
Mass
Quantity of matter in an object - a measure of the difficulty of changing the motion of an object, in kilograms (kg)
Microwaves
Electromagnetic waves between infrared radiation and radio waves on the electromagnetic spectrum
Neutron star
The highly compressed core of a massive star that remains after a supernova explosion
Neutrons
Uncharged particles of the same mass as protons. Found in the nucleus of atoms.
Nuclear fusion
The process where small nuclei are forced together to fuse and form a larger nucleus
Pressure
Force per cross section area for a force acting on a surface at right angles to the surface, measured in pascals (Pa) or newtons per square metre (N/m^2).
Protons
Positively charged particles with equal and opposite charge to the electron
Protostar
The concentration of dust clouds and gas in space that forms a star
Radio waves
Electromagnetic waves of wavelengths greater than 0.10 m
Red giant
Star that has expanded, cooled and changed colour
Red supergiant
A star much more massive than the Sun that has swollen out after the main sequence stage, before it collapses
Redshift
Increase in the wavelength of electromagnetic waves emitted by a star or galaxy due to its motion away from us - the bigger the speed, the bigger the effect
Supernova
The explosion of a massive star after fusion in its core ceases and the matter surrounding its core collapses into the centre and rebounds
White dwarf
A star that has collapsed from the red giant stage to become much hotter and denser
