GCSE Physics

• Longitudinal waves have compressions
• and rarefactions however transverse waves have crests and troughs. In transverse waves the oscillations are perpendicular to the direction of energy transfer.
• In longitudinal waves the oscillations are parallel to the direction of energy transfer.Longitudinal waves are unable to travel through a vacuum however transverse
• waves can travel through a vacuum

Compressions and rarefactions are caused by the movement of a longitudinal wave. Rarefactions are the spreading out of material as longitudinal waves pass through it Compressions are the squashing of a substance for example a medium through which longitudinal waves are passing through 

Crests and troughs are caused by themovement of a transverse wave. Troughs are the lowest point of a transverse wave.crests are the points at the maximum positive amplitude of a transverse wave

• Shock waves produced by the explosion travel out from the explosion; the particles of the air are set in motion in longitudinal waves ; the waves transfer energy from
• the explosion to the windows

• the wave speed stays the same
• the wavlength is halved  

This is when waves cross an interface between two materials so they may change direction

The wave will be diffracted through a gap similar in size to the wavelength; this does not happen to particles.

• Parts of the atmosphere are at different temperatures; the light is refracted at the interfaces and changes direction slightly; the atmosphere is moving about, so
• the light changes, twinkling.

• Waves are diffracted, through gaps of similar size to the wavelength; diffraction causes the waves to spread out and this is why shadows do not have sharp edges ; light has a very small wavelength so a very small gap is required to diffract light; Newton did not know the wavelength of light was so small; Newton was not
• looking at small enough gaps to see the effect.

So that we can compare the different sun screens directly

• 1.     All electromagnetic Waves travel at
• the speed of light , but have different frequencies , the higher the frequency
• , the shorter the wavelength the more energy the waves have 

Microwaves would heat up people who are close the oven and cook them 

It absorbs the waves so gets hotter and when it does the radio waves produce an alternating current in the aerial with a frequency the same as the radio wave itself  

It might be added to radio waves that are broadcast from a transmitter and be reflected from  the ionosphere and diffracted through valleys before reaching the aerial ; it might be added to microwaves and sent up to a satellite that receives it and transmits down to a satellite dish  

Because radio waves have a longer wavelength so are reflected from the ionosphere and diffracted by hills and valleys , however microwaves are not due to their shorter wavlength

the outer layer of the earths atmosphere . It is called the ionosphere because the air is ionised by the suns radiation 

upside down - in the case of an optical image , relative to the origional object

• The microwaves used for communications are much lower power . The microwave oven uses a particular frequency and wavelength that I strongly absorbed by water and the microwave is designed to reflect the microwaves until the food absorbs them all . There are other microwave frequencies/wavelengths that can be used for communications that do
• not have a strong heating effect . The transmitters can be placed high up where people are not close to them and they can be switched off of any workers have to go near them . Microwaves have been used in communications for many years and there aren’t cases of people being cooked . The signal from the transmitter is spread out , so the signal at the receiver is much lower 

The signal can be sent to one satellite and then around the world and back to receiver on the ground ; this is quicker than to send it in lots of steps from mast to mast , and avoids areas where there are no masts 

it would not be ethical to expose children to microwaves for research 

• Two samples of people , one of people who all use mobile phones and one of people who don’t . The samples should be very large and the people in each group should be matched ( so they should all be the same age , same sex , drink the same amount of alcohol etc.) they should be followed for many years with
• their mobile phone use remaining constant . Compare how many people in each sample get brain tumours 

Seal one phone in waterproof bag , and immerse in water ; use the other phone to phone the phone in the water ; as a control try the phone in the plastic bag before immersion 

upright

inverted 

• (a) 7m
• (b) 6m

• (a) 16
• (b)14 

when you line up the pointer exactly over its reflection then your eye is directly above the pointer and you will be reading the scale accurately 

rays of light from the object eneter the camera through the  lens , and forms an image . The image is real and inverted . Using lens gives a sharp and bright image . The image is recorded by light sensitive electronic sensors . The information is stored in some form of memory device 

the information travelling in optical fibres is more secure because unlike copper cables it is not possible to pick up radiation from outside the glass fibres . Signals in fibres dont pick up noise or unwanted signals from outside the cables . This can be a problem with copper cables