P1 Physics

• Infrared radiation is the energy transferred by electromagnetic waves
• A hot object emits more thermal (infrared) radiation than a cold object in a given time
• All objects emit infrared radiation
• The sun emits ultraviolet radiation and infrared radiation
• The greenhouse effect is caused because short wavelength infrared radiation from the sun can pass through the atmosphere. The earth absorbs this radiation, causing it to heat up, then emits long wavelength infrared radiation. Some of this radiation is absorbed by the greenhouse gases in the atmosphere causing the atmosphere to warm up. (radiation is trapped)
• Three gases that contribute to the greenhouse effect are C02, water vapour and methane

• Matt surfaces are the best emitters of infrared radiation
• Shiny surfaces are the best reflectors of infrared radiation
• A light and shiny blanket would keep a accident survivor warm because it would emit little infrared radiation and relect any thermal radiation from the survivor back inside the blanket

Matt surfaces absorb more radiation than shiny surfaces because it is uneven and has lots of cavities so the radiation hits the surface again.

Shiny surfaces reflect more because they are flat and the radiation hits the surface once.

We can get a substance to change from one state to another by changing its temperature. When a kettle boils the water turns into steam (gas). When dry ice warms up it melts (liquid).

• A gas turning to a liquid through cooling is called condensation
• States of matter are made up of particles
• When the temperature of a substance is increased the particles gain kinetic energy and move faster
• Particles in a solid held next to eachother in fixed positions

• Metals are the best conductors and materials like wool and fibreglass are good insulators because they contain pockets of trapped air

Free electrons move about randomly in metals and hold the postive ions together. 

• When a metal rod is heated the free electrons gain kinetic energy which makes them move faster
• They diffuse (spread out) and collide with other free electrons and ions in cooler parts of the metal, therefore transferring kinetic energy to them.
• So heat is transferred from the hot end to the cool end

In a non-metal solid the electrons are held in the atoms and energy transfer takes place because the atoms vibrate and shake eachother which is less effective than in a metal.

• Convection is the circulation of a fluid caused by heating it.
• For example, the hot gas surrounded by a lit candle rises and is replaced by cold air

In a domestic water system the hot water storage tank should be placed above the boiler because hot water from the tank and boiler rise up to the tap.

A sea breeze is caused by cooler air from the sea flowing in to replace warm air from the earth being radiated upwards.

• The density of of a fluid decreases when it is heated because the particles gain kinetic energy and move more causing it to expand and rise
• Heating causes circulation because hot fluids are less dense and rise and then they fall when they cool down

Convection currents trasfer energy from the hotter parts to the cooler parts

Evaporation is the conversion of water into gas by heating

• When a saucer is left in a well ventilated room water molecules escape from the water into the air so the water gradually disappears
• Weak attractive forces exist between the molecules of a liquid.
• The faster molecules which have more kinetic energy break away from the attraction of the other molecules and escape the liquid
• After they leave the liquid is cooler because the average kinetic energy of the remaining molecules has decreased
• You can increase the rate of evaporation in a liquid by: increasing temperature, surface area or the amount of air moving over a surface

Condensation is the conversion of gas into liquid by cooling

• In a steamy bathroom the water vapour in the air condenses when it hits a mirror

You can increase the rate of condensation of a gas by:

1. Increasing the surface area

2. Reducing the surface temperature

• In a steamy kitchen the rate of condensation will be greater on a big window pane
• It will also be greater if the window is cold

• A car engine needs a cooling system else it could overheat and start a fire
• A fan cools down a hot engine by increasing the flow of air over the surface of the radiator
• Cooling system of a car transfers heat from the engine to a radiator. The radiator has a large surface area which which increases the rate of energy transfer by convection in the air and radiation.

A vacuum between the two walls of a vacuum flask cuts out heat transfer by conduction and convection through walls.

• Two walls are made from glass which is poor conductor so reduces conduction. Glass surfaces are silvery to reduce radiation from the outer wall.
• The plastic cap prevents cooling by evaporation as it stops vapour loss fromt the flask.

The bigger the the temperature the difference between object and surroundings the faster the rate of energy transfer.

• The materials the object is in contact with, the objects shape and surface area can change the rate at which an object transfers energy.

When a substance is heated, its temperature rise depends on:

• the amount of energy supplied to it
• the mass of the substance
• what the substance is

The larger the object the smaller the rate of temperature change. Specific heat capacity is the amount of energy needed to raise the temp of 1kg of substance by 1 degree.

• Bricks in storage heaters (use off peak electricity) have a high SHC so they store lots of energy

Four ways to reduce rate of energy transfer at home:

• Cavity wall insulation (insulation traps air in small pockets, reducing convection currents)
• Double glazing (dry air is a good insulator so reduces conduction)
• Loft insulation (fibreglass is a good insulator and air between fibres reduces conduction)
• Aluminium foil behind radiators (reflects radiation away from wall)

A U-value tells us how effctive a matierial is as an insulator. Low U-value= better insulator

• Kinetic energy (the energy of a moving object)
• Elastic potential energy (the energy stored in a squashed spring)
• Chemical energy (the energy stored in fuel)
• Electrical energy (the energy transferred by an electric current) 
• Gravitational potential energy (the energy of an object due to its position)

When a torch is turned on the chemical energy is in the battery, electrical energy in the wires and light and heat energy from the bulb.

• When an object is dropped its GPE is transformed into kinetic energy

• When a rollercoaster climbs a hill it gains GPE
• It is transformed into other forms of energy as it goes downhill
• Air resistance and friction causes energy transfer in the form of heating 

• The conservation of energy tells us that energy cannot be created or destroyed
• The conservation of energy applies to all energy transfers
• On a bungee jump they don't return to the same height because some of the initial potential energy has been transferred into its surroundings by heating as the rope stretched then shortened again

'Useful energy' is energy that is transferred to where we want it, in the form we need it.

'Wasteful energy' is energy that is not useful energy and is not usefully transferred.

• Wasted energy spreads out to the surroundings, heating them up

Friction causes the car to slow down by applying force between the disc pad and the wheel disc.

They heat up because some of the kinetic energy of the moving car is transferred to heating the disc pads and the discs.

• Useful energy supplied to the car is eventually transferred to the road and the surrounding air 
• Energy becomes less useful after this because it is then more difficult to use it for further energy transfers (it has spread out)

Measured in…

Mass

kilograms (kg)

Weight

newtons (N)

Energy

joules (J)

• When you lift a heavy object it gains GPE
• Muscles warm up after this because some of the energy used when trying to lift an object is wasted. This then goes into the muscles as heat energy.
• Efficiency=Useful energy transferred by the device /Total energy supplied to the device(×100%) 
• A machine cant be more efficient than 100% because we can’t get more energy out of a machine than we put into it
• We can minimise waste by reducing problems for example:
• If car has a high air resistance it wastes energy to the surroundings so we could make it more steamlined
• If there is lots of friction in the wheel bearing of the go kart we can lubricate them 

• We use everyday electrical appliances for heating, lighting, creating images etc.
• The main ways ep waste energy is by transferring heat and sound to their surroundings 

Clockwork radio's invention benefited people in remote areas because clockwork radios don’t need an electricity supply or batteries, so people living in remote areas with no electricity or access to replacement batteries can listen to the radio without having to find a replacement battery.

• When a musician sings at a concert:
• sound energy -----> electrical energy -------> sound energy

• A powerful appliance is one that transfers energy very quickly 
• Power is the rate of transfer of energy
• Power (W) = energy (J) /time (s)
• Power is measured in watts (W) and equivalent to joules per second (J/s)
• 1MW (megawatt) = 1,000,000 watts (million)
• An electric lightbulb uses 100W and a railway engine uses 1MW

The useful energy out of an appliance is the same as the useful energy transferred by it per second.

• the total power is equal to the total energy to supplied to it per second
• Efficiency  =   Useful power out /Total power in ×  100%

The amount of energy supplied to an appliance depends on:

1. The power supplied to an appliance 

2. How long the appliance is used for

• the amount of energy a kW appliance uses per hour is referred to as a kilowatt-hour
• E=Px t  therefore kWh = kW x h

An electricity meter measures how much energy is used in the home

• It gives a reading of the number of kilowatt-hours of energy supplied to the house by the mains

Total cost = Number of kWh used  ×  Cost per kWh

• 'Cost effective' means getting value for money, for example, different types of cost are:
• Capital cost (buying equipment, installing equipment)
• Running cost (buying fuel, maintenence)
• Enviromental cost (cost of disposal, carbon taxes)

Insulating your home can save you money because it reduces fuel bills by reducing energy lossses from the home, e.g, loft and cavity wall insulation

• Payback time is the amount of time it takes to save the same amount of money that you spent insulting your home
• Payback time = initial cost/ savings per year

The Uk government banned the sale of filament bulbs because they use a lot more energy than any other type of bulb.

• Low-energy light-emitting diodes are the most efficient type of light bulb and they don't draw very much power and they have a long lifetime
• LEDs are expensive to buy 

• Steam is produced in a power station by burning a fuel that heats water in a boiler

Coal, oil and gas are types of fossil fuels that are obtained from long-dead biological matierial 

• An advantage of a gas fired power station is that it can be turned on very quickly
• Biofuels can be burned in small-scale, gas-fired power stations
• Methane gas can be obtained from manure, decaying rubbish and sewage works

Advantages of biofuel:

• Renewable
• A carbon neutral process

Uranium is a fuel used in nucleur power stations.

• When the nucleus of a uranium atom splits in two it releases energy and a neutron (nucleur fission)
• The core of a nuclear power reactor gets very hot because there are lots of uranium atoms releasing energy in the core
• The role of the 'coolant fluid' in a nuclear reactor is to transfer energy from the hot core to the heat exchanger. (The energy of the coolant is used to turn water into steam in the heat exchanger.)
• Fossil fuel power stations and nuclear power stations both use energy to turn water into steam, which drives a turbine that turns electricity generators

• 'Renewable energy' is energy that can never be used up
• Natrual sources of energy are carbon free to run because no fuel is used 

A wind turbine consists of an electricity generator on top of a long, narrow tower. 

• The wind drives the turbine’s blades around and this turns a generator at the top of the tower.
• The faster the wind the more energy generated 

Waves turn a generator in a wave generator by moving the generator up an down which creates a rocking motion.

• The electricity generated is transferred to shore by a cable
• Two disadvantages of wave power is that it can spoil areas of coastline and it can affect the habitats of marine life and birds

Hydroelectric power stations are usually built on hills because they generate electricity by using flowing water (downhill)

A tidal power station works by trapping each high tide and using it to turn generators.

• Tidal power and wind power both make use of turbines to drive a generator
• The Severn estuary is a promising site for a tps because it has a very high tide

• Energy is transferred to us from the sun by solar radiation
• Solar cells -----> generate electricity using the suns energy
• Solar heating panels-----> heat water directly using the suns energy
• Solar cells convert less than 10% of the energy they absorb into electrical energy. A solar power tower uses mirrors to reflect sunlight onto a water tank, which heats the water, turning it to steam.

Geothermal energy comes from energy released from radioactive substances within the earth. 

• Geothermal power stations convert geothermal energy into electricity by pumping water down to the hot rocks, which turns the water to steam and the steam is then used to drive turbines in the power station
• 'Ground heat' can be used to heat a building by pumping water underground to be heated then it is pumped around the building, which heats it. 

• The national demand for electricity suddenly increases after a popular football match ends because people go and boil the kettle 
• Carbon dioxide -----> global warming 
• Sulphur dioxide ------> acid rain
• It could take 50 years to use up the Earths oil and gas reserves 
• Carbon dioxide could be prevented of entering the atmosphere by carbon capture and storage

Nuclear versus renewable

• Nuclear power gains more energy from uranium than fossil fuels
• It does not produce greenhouse gases 
• Renewable energy sources can be used in remote areas (and no greenhouse gases) 
• It will never run out and doesn't produce radioactive waste products

Nuclear power  1. produces nuclear waste that has to be stored for centuries and 2. a nuclear reactor explosion could affect the area for many years.

Wind turbines 1. dont look appealing 2. create unwelcome noise and Tidal barrages/hydroelectric schemes affect plant and animal life  

• The National Grid: a network of cables and transformers which distribute electricity from power stations to our homes
• It transmits electricity at high voltage because a high voltage reduces power loss, which makes the National Grid more efficient
• Step up transformers: Increase the voltage of electricity leaving the power station to the National Grid voltage
• Step down transformers: Decrease the voltage at local substations for use in homes and offices

Electricity cables can't be buried underground because 1) more expensive than building pylons, 2) difficult to bury cables under rivers and canals, 3) more difficult to repair cables 

• Nuclear power stations have the longest start up time 
• Renewable energy sources are unreliable because the amount of energy they can generate can change, depending on conditions, for example, 
• Wind power ---> weak wind
• Solar power ----> night time/variable sunlight in day
• Hydroelectric power---> resevoirs running dry 
• Wave power---> weak waves on very calm days

Coil, oil and nuclear power stations are used to meet base load demand. 

• We can cope with varying demand for electricity by generating extra electricity using gas-fired power stations and pumped storage schemes
• We can make use of renewable energy when demand is low by storing energy in pumped storage schemes

• Waves are used to transfer information and transfer energy
• Microwaves and light waves are electromagnetic waves 
• Mechanical waves are water waves, sound waves, waves on a rope, seismic waves etc. 
• All electromagnetic waves travel at the same speed through a vacuum
• Mechanical waves can be transverse or longitudinal 

The vibrations of a transverse wave are perpendicular to the direction in which the waves transfer energy,  e.g, waves on a string, electromagnetic waves

The vibrations of a longitudinal wave are parallel to the direction in which the waves are travelling, e.g, a sound wave 

• We need to measure waves to find out how much energy or information they are carrying 
• The amplitude is the height of the wave from the middle
• The wavelength is from one crest to the next crest (length of one wave)
• The bigger the amplitude the more energy it is carrying

The frequency of a wave is the number of wave crests that pass a fixed point in one second.

• Measured in hertz (Hz)

Wave speed (m/s) = Frequency (Hz)  x Wavelength (m)

v = f x λ

Plane mirror: a perfectly flat mirror

• If you look straight at a plane mirror you see an exact mirror image of yourself (virtual)

Angle of incidence= angle of reflection

• Laterally inverted means back to front (not upside down) 

• Refraction is the change of direction of waves when they cross a boundary 
• When a ray of light passes into a block the angle of refraction is smaller than the angle of incidence

• When a ray of light travels from glass into air the light refracts away from the normal
• A prism splits light into colours by refracting each colour slightly differently 

• When waves move through a gap they diffract (spread out)
• The narrower the gap the more they spread out

• A ultrasonic wave is a sound wave 
• When designing an ultrasonic scanner you should consider the diffraction of ultrasonic waves, (diffract too much, unclear image)
• Radio waves are used to carry TV signals 
• When they pass a hill they diffract a little around it 
• In hilly areas the the radio waves dont spread out enough
• around the hills so people have trouble finding a signal 

• You make a sound when you speak because your vocal chords vibrate, producing sound waves
• When other sound waves reach your ears, eardrum vibrates, so you can hear sound
• Sound waves are longitudinal
• Young people can hear between 20Hz and 20,000 Hz
• If you put a ringing alarm clock in a vacuum you would hear nothing

An echo is a reflected sound, you can reduce an echo in a large hallway by)

1) Cover walls in soft fabric

2) Make wall surface uneven

• The speed of sound increases when you heat air up 
• Sound refracts up from the ground in the day because the air near the ground is warmer and downwards at night because it is warmer on the ground

• Increased amplitude = louder sound
• You can change the pitch of a musical note by changing the frequency of the soundwaves 
• Higher frequency = higher pitch

Quiet, high-pitched noise:                                     Loud, low pitched noise:

• When you play an instrument, you create sound waves by making the instrument and the air inside vibrate. Each new cycle makes the vibrations stronger and the instrument resonates at certain frequencies (recognisable notes)
• Acoustic guitars are hollow so when the guitar is played the air inside vibrates too                          

Electromagnetic waves: Electric and magnetic disturbances that transfer energy from one place to another

Speed equation: v = f × λ           (to find frequency)           f = v/λ     

• When you increase the frequency the energy of the wave increases
• Gamma rays carry the most energy

• White light is from the sun and ordinary lamps (contains all of the colours on the visible spectrum)
• The wavelength of red light is longer than violet light
• Light sensitive cells in digital cameras are called pixels

Every object emits infrared radiation

• When it hits the skin, the skin absorbs the radiation and heats up, which can damage or kill skin cells 
• Optical fibres use infrared radiation instead of light because it is absorbed less 

Microwaves are used to:  1) carry satelittle signals 2) carry mobile phone signals

A radio wave has a lower frequency than a microwave

• Radio waves carry TV, Radio, and Mobile Phone signals
• A Bluetooth signal is a radio signal at frequencies of about 2,400 million hertz
• It was set up to enable different devices to communicate with eachother

• We create a radio wave by applying an alternating voltage to an aerial
• We change the frequency of the radio wave by changing the frequency of the alternating current used to produce it

The shorter the wavelength of waves:

• the more information they carry
• the shorter their range (due to increasing absorption from the atmosphere)
• the less they spread out (they diffract less)

Microwaves carry satellite TV signals 

• Radio waves with a very long wavelength transmit national radio signals 
• (Because they have a very long range)

Mobile phone radiation may affect the brain- children have thinner skulls so their brains may be affected more.

Light and infrared radiation is used to transmit signals through an optical fibre- radiation doesn't escape the sides because light bounces off the sides

The Doppler effect: The change in wavelength and frequency that is observed when a source of waves is moving

• It was discovered in 1842
• When a light source is red-shifted it appears redder
• When a star is moving  towards us the light waves are squashed (blue-shift)
• When a star is moving away the light waves shift to a longer wavelength (red-shift)

The faster the object is moving away from us, the greater the red-shift is.

Edwin Hubble discovered that:

1) Light from distant galaxies is red-shifted

2) The further the galaxy is away from us, the more the light is red-shifted.

This tells us the universe is expanding 

• 1) The universe is still expanding after exploding suddenly from an initial point.
• 2) The universe started with the Big Bang creating space, time and matter.

Cosmic microwave  background radiation was discovered in 1965 and gives evidence for the BBT.

• CMBR was created just after the Big Bang
• It was gamma radiation when it was created 
• It is now microwave radiation because it has stretched out as the universe has expanded

Scientists think dark energy is responsible for the acceleration of the universe expanding.