Physics

Different chemical elements absorb different frequencies of light.

Each element produces a specific pattern of dark lines at the frequency it absorbs in the visible spectrum. 

When we look at light from distant galaxies, we should see the same pattern but at slighty lower frequencies - they're shfted towards the red end of the spectrum. This is called red-shift.

Measurements of red-shift suggest that all the galaxies are moving away from us very quickly.

Most distance galaxies have greater red-shift than nearer ones. This is evidence that the whole universe is expanding.

1) When something that emits waves moves towards you or away from you, the wavelengths and frequencies of the waves seem different - compared to when the source of the waves is stationary. 

2) The frequency of a source moving towards you will seem higher and its wavelength will seem shorter.

3) The frequency of a source moving away from you will seem lower and its wavelength will seem longer.

4) The Doppler effect happens to both longitundial waves (e.g sound) and transverse waves (e.g light and microwaves.)

All matter and energy in the universe was compressed into a very small space. Then it exploded from that single point and started expanding about 14 billion years ago (we use the current rate of expansion to work out the age) and still is expanding.

The 'Steady State' Theory says that the universe has always existed as it is now and it will always do. It is based on the idea that the universe appears pretty much the same everywhere. It explains the apparent expansion by suggesting that the matter is being created in the spaces as the universe expands.

The problems are that the discovery of cosmic microwave background radiation some years later was strong evidence that the Big Bang was more likely to have happened.

Sound waves are caused by vibrating objects. These vibrations are passed through the surrounding medium as a series of compressions. They are a type of longitudinal wave.

Due to the sound waves being caused by vibrating particles, the denser the medium the faster sound travels through it. Sound travels faster in solids than liquids but faster in liquids than gases.

Sound can't travel in space as it's mostly a vacuum (no particles.)

Sound waves will be reflected by hard flat surfaces. Objects such as carpets and curtains absorb sound quickly and stop it echoing in the room.

An echo is just a reflected sound wave.

You are only able the hear the echo after the original sound because the waves have to travel further so they take longer to reach your ears.

Sound waves will also refract (change direction) as they enter different spaces such as water. As they enter denser material, they speed up.

High frequency sound waves sound high pitched like a mouse whereas low frequency waves sound low pitched like a cow.

High frequency or high pitch also means shorter wavelength.

How loud or quiet a sound is depends on the amplitude of the sound wave. The bigger the amplitude, the louder the sound.

Frequency is the number of complete vibrations each second - so a wave that has a frequency of 100 hz vibrates 100 times per second.

Amplitude is the displacement from the rest position to the crest.

Wavelength is the length of a full cycle of the wave e.g from crest to crest.

Common units are kHz (1000 Hz) and MHz (1000000 Hz).

Microwaves are more commonly used for mobile phones and satellite communication. Microwaves need to be able to pass through the earth damp atmosphere and radiowaves can't do this.

Microwaves are used by satellite to give tv through a transmitter that transmits data into space, which is then picked up by a satellite dish orbiting the Earth and sent back down in a different direction, where it is recieved by a satellite dish on the surface.

Microwaves are also used for remote-sensing satellites - to see through clouds and monitor oil spills and the rate at which global warming is occuring and to see any changes in the world's ecosystem.

Infrared Waves are used in remote controls by emitting different patterns of infrared waves to send different commands to an appliance e.g a TV.

Optics fibres can carry data over long distances very quickly. They use both infrared waves and visible light. The signal is carried in pulses of light or infrared radiation and is reflected off the sides of a very narrow core from one end to the other.

1) Cameras use a lens to focus visible light onto a light sensitive film or electronic sensor.

2) The light aperture controls how much light enters the camera.

3) The shutter speed determins how long the film or sensor is exposed to the light.

Starting With The shortest wavelength and highest frequency:

1) Radiowaves (1m - 10 m)

2) Microwaves (10  m (1cm))

3) Infrared (10  m (0.01mm))

4) Visible Light (10  m)

5) Ultraviolet (10  m)

6) X-rays (10   m)

7) Gamma Rays (10   m)

All types of EM waves travel at the same speed in a vacuum but EM waves with higher frequency have shorter wavelengths.

Diffraction - The waves bend round obstacles causing the waves to spread out.

1) All waves spread out when they pass through a gap or obstacle.

2) The narrower the gap, or the longer the wavelength, the more the wave spreads out.

3) A narrow gap is one that is the same order of magnitude (or size) as the wavelength of the wave.

4) So whether a gap is narrow or not depends on the wave in question.

Refraction - When a wave changes direction as it crosses a boundary between two substances e.g air and water.

If a wave hits the boundary face on it will carry on in the same direction but if it meets a different medium at an angle, the wave changes direction - it has been refracted. 

If a wave travels along a medium (an angle of incidence is zero) it will change speed but not direction.

Reflection of light is what allows us to see things. Light bounces off objects into our eyes.

When light travelling in the same direction reflects from and uneven surface it reflects at different angles but when light travelling the same direction reflects off of an even surface then its reflected at the same angle and you get a clear reflection.

The law of reflection applies to every reflected ray:

Angle of incidence = Angle of reflection

The Normal is an imaginary line that's perpendicular (at right angles) to the surface at the point of incidence (where the light hits the surface).

1) Draw the virtual image

2) Draw the reflected ray. Draw a bold line for the part of the ray between the mirror and eye and a dotted line for the part of the ray between the mirror and virtual image.

3) Now draw the incident ray going from the top of the object to the mirror. Just draw the ray from the object to the point where the reflected ray meets the mirror.

4) Now you do steps 2 and 3 again for the bottom of the eye.

Key Points:

The image is the same size as the object.

It is as far behind the mirror as the object is infront.

The image is virtual and upright but laterally inverted.                                                                      

Most waves are transverse:

1) Light and all EM waves

2) Ripples on water

3) Waves on strings

4) A slinky spring wiggled up and down.

Law of transverse waves is as follows:

In transverse waves the vibrations are perpendicular (at 90') to the direction of energy transfer of the wave.

Examples of longitudinal waves are:

1) Sound waves and ultrasound

2) Shock waves e.g seismic waves

3) A slinky spring when you push the end

The law of longitudinal waves is as follows:

In longitudinal waves the vibrations are parallel to the direction of energy transfer of the wave.

Speed = Frequency x Wavelength

(m/s)          (Hz)                 (m)

The national grid is the network of pylons and cables that covers the whole of Britain.

The national grid takes electrical energy from power stations to where it is needed in homes and industry. It enables power to be generated anywhere on the grid.

To transmit power requires transformers aswell as pylons with huge insulators. The transformers have to step the voltage up at one end, for efficient transmission and then bring it back down to safe and usable levels.

The voltage is increased with a step up transformer and decreased using a step-down transformer.

Supply can be increased by opening more power plants or increasing their power output.

Demand can be decreased by consumers using energy-efficient appliances and being careful not to waste energy in the home e.g turning off taps and lights).

1) Oil spillages cause serious environmental problems by polluting the sea and destroy ecosystems and habitats.

2) All three fossil fuels release carbon dioxide when they are burned. All the carbon dioxide adds to the greenhouse effect, contributing towards global warming.

3) Burning coal and oil produces sulfur dioxide, which causes acid rain harmful to the environment and ecosystems.

4) Nuclear power is clean but the nuclear waste is dangerous and very difficult to dispose of.

1) Large forest area have had to been cleared to make room to grow biofuels so a lot of habitats have been destroyed.

2) The areas cleared had to have been burned so the burning of this produces carbon dioxide and methane emissions.

3) The biofuels have limited use because of the lack of area available in order to grow them.

Biofuels are renewable energy sources and generate electricity by burning them to heat up water. They can be solids e.g straw, liquids e.g ethanol or gases e.g methane.

Carbon capture and storage is used to reduce the amount of carbon dioxide building up in the atmosphere and reduce the strength of the greenhouse effect.

CCS works by taking the carbon dioxide from the power stations before its released into the atmosphere.

This can then be pumped into empty gas and oil fields where it is safely stored without adding to the greenhouse effect.

Geothermal energy is only possible in volcanic areas where hot rocks lie near to the surface and is free energy with no environmental problems.

1) Steam and hot water rise to the surface and are used to drive a generator.

2) The generator then makes electrical energy using the steam and water, which is then transferred to pylons along the national grid.

As waves come into shore they provide an up and down motion which can be used to drive a generator.

There is no pollution but they are fairly unreliable since the waves fie out when the wind drops.

Tidal barrages are big dams built across river estauries with turbines in them.

As the tide comes in it fills up the estaury to a height of several metres - it also drives the turbines. The water is allowed out of the turbines at a controlled speed.

There is no pollution and they are pretty reliable as they can happen twice a day without fail.

Hydroelectric power usually requires the flooding of a valley by building a big dam.

Rainwater is caught and allowed out through turbines. There is no pollution as such but there is a big impact on the environment as the flooding of the valley and possible loss of habitat for some species.

There is no reliablity when there is times of drought.

Pumped storage is used to pump up water to a higher reservoir to be then quickly released during periods of peack demand to supplement the steady delivery to big power stations.

Pumped storage does not create energy it just stores energy which has already been generated.

Solar cells generate electric currents directly from sunlight.

There is no pollution and are a very reliable source of energy in sunny areas but can still be cost effective in cloudy places like Britain.

Each turbine has its own generator within and the electricty is generated directly from the wind turning the blades which turns the generator.

There is no pollution but they do spoil the view however if you remove the turbines no harm is done to the land and the view return to normal. They can be noisy and are somewhat unreliable as there will be no power generated when the wind stops.

The non-renewables are the three fossil fuels and nuclear:

1) Coal

2) Oil

3) Natural Gas

4) Nuclear Fuels

These will all run out one day and they all do damage to the environment but provide most of our energy.

The renewables are:

1) Wind                                      5) Solar

2) Waves                                   6) Geothermal

3) Tides                                     7) Food

4) Hydroelectric                         8) Biofuels

These will never run out and most of them do damage to the environment but in a less nasty way than non-renewables but they dont provide much energy and some of them are unreliable as they depend on weather.