# Physics - P1 Revision

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## Energy Transfer by Heating

Infrared waves are part of the electromagnetic spectrum, we can detect it with our skin as it makes us feel warm.

The hotter an object is the more infrared radiation it emits in a given time.

Infrared radiation can travel through a vacuum and therefore this is how we get energy from the sun.

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## Energy Transfer by Heating - 2

Dark, matt surfaces are good absorbers of infrared radiation, therefore if left out in the sun an object of this type will be hotter can something shiny and white.

Dark, matt surfaces are also good emitters of infrared radiation, so an object of this type will cool down faster than something shiny and white.

Light, shiny surfaces are good reflectors of infrared radiation.

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## Energy Transfer by Heating - 3

• States of Matter

The three states of matter are solid, liquid and gas. We can change between these states by heating or cooling them.

In a solid the particles vibrate about fixed positions keeping it in a fixed shape.

In a liquid the particles are in contact with eachother but are arranged randomly so a liquid doesn't have a fixed shape and can instead flow.

In a gas the particles are far apart and can move around much faster therefore there is no fixed shape and gas can also flow. The density of gas is much less than that of a solid or liquid.

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## Energy Transfer by Heating - 4

• Conduction

Conduction occurs in many solids as liquids and gases are bad conductors.

If a solid is heated the particles gain kinetic energy and vibrate more, the energy is then passed to other particles and therefore the energy is passed through the solid.

This process occurs in metals.

In addition when metals are heated their free electrons move through the metal colliding with other particles.

Poor conductors are called insulators.

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## Energy Transfer by Heating - 5

• Convection

Convection occurs in fluids.

When a fluid is heated it expands and the fuild becomes less dense and rises. The warm fuild is replaced by colder fluid and this creates a convection current.

Convection currents can occur on different scales.

They are the cause of onshore and offshore breezes.

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## Energy Transfer by Heating - 6

• Evaporation and Condensation

Evaporation is when a liquid turns into a gas and this takes place when the particles with the most energy escape from the liquids surface and enter the air.

This reduces the temperature of the liquid because the particles left have the least kinetic energy.

The rate is increased by:

• Increasing the surface area of the liquid
• Increasing the temperature of the liquid
• Creating a draught of air across the liquid's surface

Condensation is when a gas turns into a liquid, this often takes place on cold surfaces.

The rate is increased by:

• Increasing the surface area
• Reducing the surface temperature
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## Energy Transfer by Heating - 7

• Energy Transfer by Design

The greater the temperature difference between an object and its surroundings the greater the rate at which of energy transfer.

The rate also depends on:

• The materials the object is in contact with
• The object's shape
• The object's surface area

Sometimes we want to maximise the rate of energy transfer to keep things cool. In order to do this we may use:

• Things that are good conductors
• Things that are painted a dull black
• Things that have air flow around them
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## Energy Transfer by Heating - 7.2

• Energy Transfer by Design

Sometimes we want to minimise the rate of energy transfer to keep things hot. To do this we may use:

• Things that are good insulators
• Things that are painted white and shiny
• Things that prevent convection currents by trapping air in small pockets
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## Energy Transfer by Heating - 8

• Specific Heat Capacity

When we heat a substance we transfer energy to heat it. The specific heat capacity is the amount of energy needed to heat 1kg of a substance by 1 degree celsius.

Different substances have different specific heat capacities, the greater the specific heat capacity the more energy needed.

The greater the mass of substance being heated the more energy that will also be needed.

The equation is E = m x c x theta

E = energy transferred in J

m = mass in kg

c = specific heat capacity in J/kg degrees celsius

theta = temperature change in degrees celsius

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## Energy Transfer by Heating - 9

• Heating and Insulating Buildings

Most people want to minimise the amount of energy transfer out of their homes to reduce bills.

This can be done by fitting:

• Fibreglass loft insulation to reduce conduction
• Cavity wall insulation to reduce convection
• Double glazing to reduce conduction
• Draught proofing to reduce convection

The U-Value of a material tells us how much energy per second passes through it, the lower the value the better it is as an insulator.

Solar heating panels contain water heated by infrared radiation from the sun this can then be used to heat buildings.

They are cheap to run however expensive to install and buy also they do not work at night.

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## Using Energy

• Forms of Energy

Energy exists in a variety of forms these being:

• Gravitational Potential
• Sound
• Heat
• Electrical
• Light
• Nuclear
• Elastic Potential
• Chemical
• Kinetic

Energy can be transferred from one form to another.

An object above ground always has gravitational potential energy.

A falling object transfers gravitational potential energy to kinetic energy.

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## Using Energy - 2

• Conservation of Energy

It is not possible to create or destroy energy it is only possible to transform it from one type of energy to another.

This means that the total amount of energy is always the same, and this is called the conservation of energy.

For example when an object falls gravitational potential energy is transferred into kinetic energy.

And stretching an elastic band transfers chemical energy to elastic potential energy.

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## Using Energy - 3

• Useful Energy

A machine is something with transforms energy from one type to another.

The energy we get out is either useful or wasted.

Both the useful and wasted energy will eventually be lost to the surroundings and make them warm up.

Energy is often wasted becuse of friction between parts of the machine, the energy warms up the machine and the surroundings.

Sometimes friction may be useful for example in the brakes of bicycle or a car. Some of the kinetic energy is transferred to energy heating the brakes.

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## Using Energy - 4

• Energy and Efficiency

Energy is measured in joules J.

The energy supplied to a machine is called the input energy we know that the useful energy and wasted energy add up to this.

The less energy that is wasted the more efficient the machine is.

The equation is: Efficiency = Useful energy / Total energy supplied x 100%

The efficiency can be left as a fraction or multiplied by 100 to give a percentage.

No appliance can be 100% efficient.

The energy transfer through an appliance can be represented as a sankey diagram.

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## Electrical Energy

• Electrical Appliances

Electrical appliances are extremely useful they transform electrical energy into whatever form at the flick of switch.

Common electrical appliances are:

• Lamps - produce light
• Electric mixers - produce kinetic energy
• Speakers - produce sound energy
• Televisions - produce light and sound energy

Many electrical appliances transfer energy by heating, this may be useful but it is usually wasted energy.

Appliances should be designed to waste as little energy as possible.

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## Electrical Energy - 2

• Electrical Power

The power of an appliance is the rate at which it transfers energy.

The unit of power is watts W.

1 kilowatt = 1000 watts

The equation is: P = E/t

P is power in watts

E is energy in joules

t is time taken in seconds for the energy to be transferred

We can also write the effiency equation in terms of power:

Efficiency = Useful power out/Total power in x 100%

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## Electrical Energy - 3

• Using Electrical Energy

Companies that supply mains electricity charge customers for the amount of electricty used.

Due to large numbers being used energy is measured in kilowatt-hour kWh.

A kilowatt hour is the amount of energy transferred by a one kilowatt appliance when used for one hour.

The amount of energy transferred equation is: E = P x t

E = energy transferred in kilowatt-hours

P = power of the appliance in kilowatts

t = time taken in hours for the energy to be transferred.

The cost is calculated by: Total cost = Number of kWh x Cost per kWh

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## Electrical Energy - 4

• Cost Effectiveness Matters

To compare the cost effectiveness we must take into account a variety of factors.

These may include:

• Cost of buying the appliance
• Cost of installing the appliance
• Running costs
• Maintenance costs
• Environmental costs
• Interest charged on a loan to buy the appliance

Many people buy newer more efficient appliances to reduce their energy bills.

The payback time is the time it taes for an appliance or installation to pay for itself in terms of energy savings.

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## Generating Electricity

• Fuel for Electricty

In most power stations water is heated to produce steam and this steam drives a turbine, which is coupled to an electrical generator which produces the electricity.

The energy can come from fossil fuels which are obtained from long-dead biological matter.

In some gas-fired power stations hot gases may drive the turbine directly.

Some biofuels can be used in small scale gas-fired power stations and they are a renewable source of energy.

In nuclear power stations the fuel used in either uranium or plutonium.

The process which creates energy is nuclear fission which happens to the nucleus.

The energy is used to heat water which then turns into steam.

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## Generating Electricity - 2

• Energy from Wind and Water

These forms of energy are renewable because the source can never be used up.

We can use energy from the wind and water to drive turbines directly.

In a wind turbine the wind makes blades rotate which then drive a generator.

Electricity can be produced from energy obtained from falling water, waves or tides.

At a hydroelectric power station water is allowed to flow downhill where it turns turbines.

In a pumped storage power station water is pumped back up the hill in times of low demand and then it can be released to flow in times of high demand.

Wave power uses the movemnet of waves to drive a floating turbine that turns a generator.

Tidal power creates energy by trapping water at high tide and then when it is released to fall down to lower sea level it drives turbines.

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## Generating Electricity - 3

• Power from the Sun and the Earth

Solar energy travels from the Sun to Earth as electromagnetic radiation.

A solar cell transfers this energy into electrical energy, each cell provides a small amount of energy so they are good for powering small devices such as watches and calculators.

Water flowing through a solar panel is heated directly by energy from the sun.

A solar power tower uses thousands of mirrors to reflect sunlight onto a water tank in order to heat it and produce steam.

Geothermal energy is produced inside the Earth by radioactive processes and this heats the surrounding rock. Large holes are then drilled and cold water is pumped in to be heated by this rock.

The steam prodcued drives the turbine which turns the generator.

In a few parts of the world hot water comes to the surface naturally which can then be used to heat buildings nearby.

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## Generating Electricity - 4

• Energy and the Environment

Non renewable resources are being used up at a much faster rate than they are being produced.

Oil and gas will probably run out in the next 50 years however coal will last much longer than this.

Renewable energy sources will not run out and they can be produced as fast as they are being used up.

Scientists are investigating ways to reduce the environmental impact of using fossil fuels.

There are advantages and disadvantages of using each type of energy source.

For example polluting gases such as CO2 and SO2 are produced by non renewable resources.

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## Generating Electricity - 5

• The National Grid

The National Grid distributes all the electricity across Britain, it is a network of pylons and cables that connect power stations to all sorts of buildigs.

As the whole country is connected it power stations can be switched in or out depending on the demand.

There are two types of cables those underground and those overhead.

The National Grids voltage is 132000V or more and power stations produce a voltage of 25000V.

The electricity produced by power stations passes through a step-up transformer to increase the voltage before it passes through the National Grid this is to reduce energy wastage.

Then at local sub-stations it passes through a step-down transformer to reduce the voltage to 230V as this prevents dangerous amunts being given to consumers.

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## Generating Electricity - 6

• Big Energy Issues

A constant amount of electricity is provided by fossil fuels and power stations this is called base load demand.

The demand varies during the day and in different seasons.

Gas-fired power stations and pumped-storage power systems can meet variations in demand.

Different types of power station have different start up times.

Gas-fired have the shortest start up time, and nuclear have the longest.

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## Waves

• The Nature of Waves

We use waves to transfer energy and information. The direction in which the wave travels is the direction in which they transfer energy.

For a transverse wave the oscillation of the particles is perpendicular t the direction in which the wave travels.

For a longitudinal wave the oscillation of the particles is parallel to the direction of travel of the wave. Also longitudinal are made up of compressions and rarefractions.

Electromagnetic waves can travel through a vacuum as no particles are needed as the oscillations are perpendicular they are also transverse waves.

Mechanical waves can be either transverse or longitudinal.

Sound waves are longitudinal.

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## Waves - 2

• Measuring Waves

The amplitude of a wave is the height of the wave from the middle to the wave crest or trough.

The wavelength of a wave is the distance from one crest to another.

The frequency of a wave is the number of wave crests passing a point in one second and it is measured in Hz.

The speed of a wave is calculated by the equation: v = f x wavelength

v = the wave speed in metres per second m/s

f = the frequency in hertz Hz

wavelength = the wavelength in metres m

The wavelength of a longitudinal wave is the distance between the middle of one compression to the next and the frequency is the number of compressions passing a point in one second.

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## Waves - 3

• Wave Properties: Reflection

An image is formed in a plane mirror by the incident ray going towards the mirror and then the reflected ray comes away from the mirror.

The normal line is perpendicular to the mirror at the point where the incident ray meets the mirror.

The angle of incidence is between the incident ray and the normal.          These two angles

The angle of reflection is between the reflected ray and the normal.                are equal.

A real image is formed on a screen because the rays of light that produce the image actually pass through it.

A virtual image cannot be formed on a screen becasue the rays of light that produce the image only appear to pass through it.

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## Waves - 4

• Wave Properties: Refraction

Waves change speed when they cross a boundary between substances the wavelength changes but the frequency remains the same.

Refraction is a property of all waves.

When light enters a more dense substance it slows down and the ray changes direction towards the normal.

When light enters a less dense substance it speeds up and the ray changes direction away from the normal.

However if the wave is travelling along the normal then it will not change direction.

Different colours have different wavelengths and therefore a spectrum can be displayed via refraction. This is called dispersion. Violet is refracted the most and red is refracted the least.

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## Waves - 5

• Wave Properties: Diffraction

Diffraction is the spreading of waves when they pass through a gap or round an obsticle and this happens to all waves.

The effect is most noticible is the wavelength of the waves is about the same size as the gap or obsticle.

TV signals which are carried by radio waves may not be able to get to people living in hilly areas because they are blocked by hills, therefore they will diffract around the hill if they do not diffract enough the signal will be poor.

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## Waves - 6

• Sound

Sound is caused by mechanical vibrations in a substance and travels as a wave.

It can travel through solids, liquids and gases. Solids fastest and gases slowest.

They cannot travel through a vacuum because it requires particles.

The range of frequencies which can be heard by humans is from 20Hz to 20000Hz.

Sound waves can be reflected to produce echoes.

Only hard, flat surfaces reflect sound, soft things absorb it.

Sound can be refracted and takes place between layers of air at different temperatures.

Sound waves can also be diffracted.

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## Waves - 7

• Musical Sounds

The pitch of a note depends of the frequency of the sound waves.

The higher the frequency the higher the pitch of the sound.

The loudness of a sound depends on the amplitude of the sound waves.

The greater the amplitude the louder the sound.

Differences in waveform can be shown on a oscilloscope.

Different instruments produce different waveforms and this causes them to sound different from eachother.

Vibrations created in an instrument produce sound waves.

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## Electromagnetic Waves

• The Electromagnetic Spectrum

All electromagnetic waves travel through space at the same speed but they have different wavelengths and frequencies.

Different wavelengths are reflected, absorbed or transmitted differently by different substances and types of surface.

The higher the frequency of a wave the more energy it transfers.

All electromagnetic waves travel through space at a wave speed of 300 million m/s.

The order is: Radiowaves, Microwaves, Infrared, Visible Light, Ultraviolet, X-rays and Gamma Rays.

As you move from the bottom to the top the energy decreases, wavelength increases and frequency decreases.

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## Electromagnetic Waves - 2

• Light, Infrared, Microwaves and Radiowaves

Visible light is seen by our eyes and each of the different wavelengths represents a different colour. A mixture of all the colours is known as white light.

Infrared radiation is given out by all objects and objects such as remote controls use infrared.

Microwaves can pass through the atmosphere and so are used to send signals to and fro satellites for moblie phone networks.

Radiowaves transmit radio and terrestrial TV programs and carry mobile phone signals.

Microwave radiation and radio waves can penetrate the skin. This can heat internal organs and may damage them.

Infrared radiation is absorbed by skin, too much will burn the skin.

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## Electromagnetic Waves - 3

• Communications

The shorter the wavelength of the waves the more information they carry, the shorter their range the less they spread out.

Mobile phones communicate with a local mobile phone mast using microwaves.

Some scientists believe the radiation from mobile phones may affect the brain.

Optical fibres are used to transmit visible light or infrared radiation.

They are better for communications because they are more secure than radio wave and microwave transmissions.

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## Electromagnetic Waves - 4

• The Expanding Universe

The Doppler Effect

• When a source moves away from an oberver the oberved wavelength increases and the frequency decreases.
• When a source moves towards an observer the observed wavelength decreases and the frequency increases.

The Doppler effect is also shown by pitch as something moves away the pitch is lower or as it moves towards the pitch is higher.

Light observed from distant galaxies has been shifted towards the red end of the spectrum and thsi is known as red-shift.

A blue-shift would show that a galaxy is moving towards us.

The further away a galaxy the bigger the red shift and the faster it is moving. As all galaxies are doing this the Universe is expanding.

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## Electromagnetic Waves - 5

• The Big Bang

Red-shift gives evidence that the universe is expanding.

If it is now expanding outwards there must have been a massive explosion at an initial point this is the Big Bang Theory.

If the universe began with the Big Bang then gamma radiation would have been produced and as the universe expands it would have become lower energy radiation.

This is now as Cosmic Microwave Background Radiation amd is produced by the Big Bang.

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