Physics - Unit 1

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What is infrared radiation?
Electromagnetic waves between visible light and microwaves in the electromagnetic spectrum
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What detects infrared radiation?
Our skin
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What emits infrared radiation?
All objects, the hotter the object the more infrared radiation it emits in a given time
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How do get our energy from the sun?
Infrared radiation can travel through a vacuum therefore space
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What are dark, matt surfaces good at?
Good absorbers of infrared radiation / emitters of IR
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What are light shiny surfaces good at?
Good reflectors of IR
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What are the three states of matter?
Solid / Liquid / Gas
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In a solid...
Particles vibrate in a fixed position > fixed shape / strong forces of attraction hold particles close together / least energy
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In a liquid...
Weaker forces of attraction so particles aren't held in a fixed position / liquids can flow / particles are in contact / particles move randomly / moderate energy
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In a gas...
Negligible forces of attraction / particles are far apart / move randomly / most energy
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What is conduction?
When particles in a solid are heated they gain energy and vibrate > the particles therefore collide with each other > energy is transferred through solid
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Why are metals the best conductors?
They have delocalised electrons that are free to move around the structure, transferring energy by colliding with other particles
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What are poor conductors called?
Insulators (non-metals)
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What is convection?
Occurs in fluids > as parts of fluid are heated the particles gain more energy and move away from each other > they become less dense and rise > they then cool and become more dense and fall > this transfers energy from hotter parts to colder parts
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What is evaporation?
When molecules in a liquid gain kinetic energy they move around faster > they may gain enough energy to overcome the weak forces which attract them to each other > they break free and escape liquid
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Why does evaporation cause cooling?
When the energetic molecules leave the liquid the average kinetic energy of the remaining particles decreases so the temperature of the liquid decreases
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What are the factors affecting the rate of evaporation?
SA/temperature of liquid / air moving across surface of liquid
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What is condensation?
When molecules in a gas lose energy they turn into a liquid > this happens when they hit a cold surface
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Where does condensation often take place?
Cold surfaces such as windows and mirrors
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What are the factors affecting the rate of condensation?
SA of the surface in contact / temperature of surface in contact
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Liquid > gas
Vaporise
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Solid > gas
sublimes
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What does the rate of energy transfer to/from an object depend on?
The shape/size/type of material of the object / materials the object is in contact with / the temperature difference between the object and its surroundings
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How do we maximise the rate of energy transfer?
Use good conductors / objects painted dull black / have the air flow around them maximised
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How do we minimise the rate of energy transfer?
Use good insulators / objects that are white and shiny / prevent convection currents by trapping air in small pockets
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What is the structure of a vacuum flask?
Vacuum prevents conduction and convection / inside surfaces silvered to stop radiation / sponge pad and plastic cover for protection / double walled glass/plastic container / plastic cap
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What is the specific heat capacity of a substance?
The amount of energy required to raise the temperature of 1 kg of the substance by 1C
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The greater the mass of a substance being heated...
The more energy required for each degree temperature change
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What is the unit for specific heat capacity?
J/kg degrees
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How do we minimise the rate of energy transfer out of houses?
Fibreglass loft insulation / double glazing (through windows) to reduce conduction / Cavity wall insulation which traps air / draught proofing to reduce convection / aluminium foil behind radiators to reflect I
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What is the U-value of a material?
How much energy per second passes through 1m squared for 1C temperature difference
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How do solar heating panels work?
They contain water that is heated by radiation from the sun > this water is then used to heat buildings or provide hot water
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What is the advantage of solar panels?
They are cheap to run because they do not use fuel
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What are the disadvantages of solar panels?
They are expensive to buy and install > water is not heated at night
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What are the different forms of energy?
Sound / kinetic / light / electrical / nuclear / gravitational potential / elastic potential / chemical
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Energy can be...
Transferred from one form to another
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What does conservation energy mean?
Energy can't be created or destroyed, the total amount of energy is always the same
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What is a machine?
Something that transfers energy from one place to another or from one form to another
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The energy we get out of a machine consists of...
Useful energy -which is transferred to the place we want in the form we want / Wasted energy - which is not usefully transferred
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What happens when useful and wasted energy are transferred to the surroundings?
The surroundings get warmer
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As energy spreads out...
It gets more difficult to use for further energy transfers
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What is energy measured in?
Joules
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No machine can be...
100% efficient
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What is a Sankey diagram?
An energy transfer diagram
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Electrical appliances can...
Transfer electrical energy into useful energy at the flick of a switch
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What are the uses of electrical appliances?
Heating / lightning / making things move / creating sound and visual images
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Appliances should be designed to...
Waste as little energy as possible
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What is the power of an appliance?
The rate at which it transfers energy
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What is the unit for power?
Watts
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How many watts does a kilowatt equal?
1000 watts
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What is the kilo-watt hour?
The energy supplied to a kW appliance in 1 hour
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What is the equation for working out the cost of electrical energy supplied?
Total cost = number of kWh x cost per kWh
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What does cost effectiveness mean?
Getting the best value for money
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What costs do we need to consider to compare the cost effectiveness of different appliances?
Cost of buying/installing / running costs / maintenance/environmental cost / interest charged on a loan to buy the appliance
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What is payback time?
The time it takes for an appliance or installation to pay for itself in terms of energy savings
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What happens in power stations?
Water is heated to produce steam > the steam drives a turbine > which is linked to an electrical generator > this produces the electricity
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What are three fossil fuels?
Coal / oil / gas
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What is a bio-fuel?
Any fuel that is obtained from living or recently living organisms
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What fuel is used in nuclear power stations?
Uranium or plutonium
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What heats the water in a nuclear power station?
The nucleus of an uranium atom undergoes a process called nuclear fission, which releases energy > this energy heats the water turning into steam
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What is renewable energy?
Energy from sources that never run out including wind / wave / tidal / hydroelectricity / geothermal and solar energy
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In a wind turbine...
The wind passing over the blade makes them rotate and drive a generator at the top of a narrow tower
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What is hydroelectric power?
At an hydroelectric power station, water collected in a reservoir. This water is allowed to flow downhill and turn turbines at the bottom of the hill
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What happens in a pumped storage system?
Surplus energy is used to pump the water back up the hill to top reservoir
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What is wave power?
Uses the movement of the waves on the sea to generate electricity. The movement drives a floating turbine that turns a generator > Then the electricity is delivered to the grid system on shore by a cable
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What is tidal power?
The water at each high tide can be trapped behind it > when the water is released to fall down to the lower sea level, it drives turbines
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A solar cell...
Can transfer the energy from the sun into electrical energy > water flowing through a solar heating panel is heated directly by energy from the Sun
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What is geothermal energy?
It is produced inside the Earth by radioactive processes and this heats the surrounding rock > in volcanic areas, very deep holes are drilled and cold water is pumped down to the hot rock > there it is heated and comes back to the surface as steam
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What is the national grid?
A network of cables and transformers used to transfer electricity from power stations to consumers
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What is a step-up transformer used for?
To increase the voltage from the power stations before the electricity is transmitted across national grid
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What is a step-down transformer used for?
To reduce voltage from the national grid for use in homes and offices
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What is a base load?
Constant amount of electricity generated by power stations
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Nuclear, coal, and oil power stations...
meet base-load demand
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What power station has the shortest start-up time?
Gas-fired power stations
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What power station has the longest start-up time?
Nuclear power stations
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We use waves to...
Transfer energy and information
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What are the features of a transverse waves?
The oscillation of the particles is perpendicular to the direction in which the wave travels > all electromagnetic waves are transverse
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What are the features of a longitudinal wave?
The oscillation of the particles is parallel to the direction of travel of the wave / a longitudinal wave is made up of compressions and rarefractions / a soundwave is a longitudinal wave
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Mechanical waves can be...
Transverse or longitudinal
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What is the amplitude of a wave?
The height of the wave crest or the depth of the wave trough from the position at rest
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What is the wavelength of a wave?
The distance from one crest to the next crest
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What is the frequency of a wave?
The number of wave crests passing a point in one second
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What is the unit for frequency?
Hertz
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What is the angle of incidence?
Equals the angle of reflection
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What is the normal line?
The line perpendicular to the mirror
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What is refraction?
The change of the direction of a wave when they travel across a boundary
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Waves change speed when they...
Cross a boundary
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If the speed is reduced...
Refraction is towards the normal
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If the speed is increased...
Refraction is away from the normal
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Violet light is refracted...
The most
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Red light is refracted...
The least
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What is diffraction?
It is the spreading out of waves when they pass through a gap or round obstacles
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The narrower the gap...
The greater the diffraction
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What is sound caused by?
Mechanical vibrations in a substance
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Sound waves cannot...
Travel through a vacuum
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Sound waves can be reflected to produce...
Echoes
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The pitch of a note depends on...
The frequency of the sound waves. The higher the frequency the higher the pitch
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The loudness of a sound depends on...
The amplitude of a wave. The greater the amplitude, the lou der the sound
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What is the order of the electromagnetic spectrum?
Gamma rays > x-rays > ultraviolet > visible light > infrared > microwaves > radio waves
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What is the wave speed of all electromagnetic waves?
300 million metres per second
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What is the equation for the speed of a wave?
Speed=frequency x wavelength
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What is visible light detected by?
Our eyes
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What are microwaves used in?
Communications - they are used to send signals to and from satellites and within mobile networks
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What do radiowaves transmit?
Radio and TV programmes and carry mobile phone signals
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Microwave radiation and radio waves can penetrate...
Our skin, this can heat internal organs and may damage them
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Infrared radiation is absorbed...
By skin, too much will burn your skin
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The shorter the wavelength of waves...
The more information they carry, the shorter the range, the less they spread out
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What are optical fibres?
Very thin flexible glass fibres. We transmit signals through them by the repeated total internal reflection of visible light
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Why are optical fibres useful in commuications?
Carry much more information and are more secure than radio waves and microwave transmissions
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What is the Doppler effect?
The change in the wavelength and frequency of a wave which is moving relative to the observer
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How does the observed wave change if the distance between the wave source and the observer is increasing?
The wavelength increases / the frequency decreases
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How does the observed wave change if the distance between the observer is decreasing
The wavelength decreases / the frequency increases
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What happens to the light we observe from distant galaxies which are moving away from us?
The wavelength of the light decreases and its frequency decreases. Red light has the longest wavelength so the light's wavelength increases, it is shifted towards the red end of the spectrum
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What happens to the light we observe from galaxies which are moving towards us?
The light's wavelength decreases and its frequency increases. Violet light has the shortest wavelength, as the light's wavelength decreases, the light is shifted towards the blue end of the spectrum
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How can we see the effects of these shifts in light's wavelength?
By observing the shift of the 'dark lines' of the spectrum from a galaxy
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What are dark lines?
Areas of the spectrum which don't emit light because that wavelength of light has been absorbed in the source
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What does red-shift tell us about the universe?
The further away the galaxy, the bigger the red-shift. Distant galaxies are moving away from us, the most distant are moving the fastest, every direction > the universe is expanding
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What is the Big Bang theory?
If the universe is now expanding outwards, then it must have started with a massive explosion at a very small initial point
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What is CMBR?
CMBR is cosmic microwave background radiation. These are microwaves coming from every direction in space
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What is the only theory which can explain the existence of CMBR?
The Big Bang - states that is the universe began with the big bang, high gamma-ray radiation would have been produced. As the universe expanded, the doppler effect meant that the radiation's wavelength increased and frequency decreased
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Other cards in this set

Card 2

Front

What detects infrared radiation?

Back

Our skin

Card 3

Front

What emits infrared radiation?

Back

Preview of the front of card 3

Card 4

Front

How do get our energy from the sun?

Back

Preview of the front of card 4

Card 5

Front

What are dark, matt surfaces good at?

Back

Preview of the front of card 5
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