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how are transverse and longitudinal waves different ?
- 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
explain what is meany by the words compressions and rarefactions
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
explain what is meant by the terms crests and troughs
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
after an explosion all the windows in a nearby building are broken . How did this happen
- 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
If the frequency of waves is doubled what happens to the wave speed and the wavelength
- the wave speed stays the same
- the wavlength is halved
Waves are refracted at an interface . What does refraction mean
This is when waves cross an interface between two materials so they may change direction
how would you show that an unknown radiation was a wave and not a stream of particles
The wave will be diffracted through a gap similar in size to the wavelength; this does not happen to particles.
light from the stars twinkles because it is refracted as it passes through the atmosphere . Explain what this means and how it happens
- 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.
Sir Isaac Newton said that light was not a wave because shadows had sharp edges . Explain why waves do not give shadows with sharp edges , and why scientists today say that light is a wave
- 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.
sun screens are all rated using the same test to see how much UV is prevented from reaching the skin . Why is it important to use the same test
So that we can compare the different sun screens directly
describe the EM spectrum
- 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
why do microwave ovens have a safety lock to prevent them operating while the door is open
Microwaves would heat up people who are close the oven and cook them
a radio aerial recieves a radio broadcast . Describe two things that happen to the metal aerial
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
describe the different ways that a television signal might reach your TV set
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
Explain why Radio waves can be recieved over a large area but microwaves need repeating transmitters on hills and buildings
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
a student says that we should not use microwaves for communications because microwaves cook meat so they will cook us . Explain why the student is wrong in this conclusion .
- 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
why are satellites used for international phone calls
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
why has there been no study of the effects of mobile phones on the health of children who use them
it would not be ethical to expose children to microwaves for research
describe how scientists could research whether there is a link between mobile phone use and brain tumours
- 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
describe how you could use two mobile phones to find out whether microwaves are absorbed by water
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
which way up is the image in a plane mirror
which way up is the image in a camera
an opticians chart is on the wall 1m behind the patient's head . The patient sees the chart in the mirror , which is 2.5m away in the front of the patient . How far away from : (a) the chart (b) the patient does the image of the chart appear to be
an opticians chart is on the wall 2m behind the patient's head . The patient sees the chart in the mirror , which is 6 away in the front of the patient . How far away from : (a) the chart (b) the patient does the image of the chart appear to be
the photograph shows a meter with a mirror behind the pointer .
Explain how the mirror helps to read the meter accurately
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
write a wiki page to describe how a digital camera produces and image of the object being photographed
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
what are the advanatges of using fibre optic cables instead of copper cables for telephone wires
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
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