Waves - GCSE Flashcards
what do all waves have? (4 things)
- wavelength
- frequency
- amplitude
- speed
what is the wavelength of a wave?
the distance from one peak to the next
what is the frequency of a wave?
how many complete waves there are per second (passing a certain point).
what is the frequency of a wave measured in?
it is measured in herts (Hz). 1 Hz is 1 wave per second
what is the amplitude of a wave?
the height of the wave (from rest to crest)
what is the speed of a wave?
the speed is how fast the wave moves
what is the period of a wave?
the time it takes (in seconds) for one complete wave to pass a point
describe the diagram of a wave with all its parts (wavelength, frequency…)
https://d1e4pidl3fu268.cloudfront.net/9d324e47-7a60-42af-b3c2-928c12bfed9a/waves.crop_487x366_0,0.preview.png
what is usually the characteristic of the frequency of a wave?
it usually has a high frequency and it is given in an awkward unit like kHz or MHz
most waves are what?
transverse
how is the vibration of transverse waves like?
in transverse waves the vibrations are at 90 degrees to the direction energy is transferred by the wave
what are 4 examples of transverse waves?
- light and EM waves
- a slinky spring wiggled up and down
- waves on strings
- ripples on water
what is another type of wave other than transverse wave?
longitudinal wave
what are 3 examples of longitudinal wave?
- sound and ultrasound
- shock waves
- a slinky spring when you push the end
how is a longitudinal wave like?
in a longitudinal wave the vibrations are along the same direction as the wave transfers energy
what do all waves carry and transfer?
energy
where do waves carry and transfer energy to?
to the direction they are travelling
what is an example of a wave transferring energy?
microwaves in an oven make things warm up, their energy is transferred to the food you’re cooking
what do sound waves make things do?
they make waves vibrate or move
what is something waves can be used as?
they can be used as signal to transfer information from one place to another
what are wave fronts?
they are imaginary planes that cut across all the waves.
what is the distance between one wavefront equal to?
it is equal to one wavelength
how will the frequency of a wave be if the wave source is moving towards an observer? what will be the wavelength?
- Doppler Effect -
the frequency will be higher and the wavelength will be shorter than the original wave emitted by the source
how is the frequency of a wave if a wave source is moving away from an observer? what will be the wavelength?
- Doppler Effect -
the frequency will be lower and the wavelength will be longer than the original wave emitted by the source
what is the Doppler effect?
when the frequency is higher when the source is moving towards you, and lower when the frequency is moving away from you
what is a example of the Doppler effect?
-> sound waves of a car
- the sound waves from a stationary car are equally spaced
- the sound waves for a moving car is longer on where the car has just passed (the sound is higher), and shorter where the car is closest to (the sound is more quiet)
what is a shorter way of saying electromagnetic waves?
EM waves
what difference do electromagnetic waves with different wavelengths have?
they have different properties
how many group types are electromagnetic waves grouped into?
7
what are the seven groups electromagnetic waves are grouped to?
- radio waves
- microwaves
- infrared waves
- visible light
- ultraviolet
- x rays
- gamma rays
what do all type of EM rays have in common?
they are transverse waves and they travel at the same speed through free space
what do different colours of visible light depend on?
it depends on the wavelength.
red -> longest wavelength (lowest frequency)
violet -> shortest wavelength (highest frequency)
what are the colours (in order from lowest frequency to highest) of visible light?
1) red
2) orange
3) yellow
4) green
5) dark purple
6) purple
7) violet
what are radio waves used mainly for?
communications
why can long-wave radios be transmitted a long way?
because long wavelengths aren’t bent around the curbed surface of the earth
why can short-wave radio signals can be received at long distances from the transmitter?
They can be received because they are reflected from the ionosphere (a layer of the Earth’s atmosphere)
what is the length of a wavelength of a TV and FM radio broadcasting?
they have very short wavelengths (10cm - 10m)
how do TV and FM radio broadcasting get reception?
they need to be in direct sight of the transmitter since the signal does not bend around hills
what is the length of microwaves?
their wavelength is about 1 - 10cm
what can microwaves be used for?
communication
what waves do satellite communication (including satellite TV signals and satellite phones) use?
it uses microwaves
explain the process for a satellite TV to receive information
For a satellite TV the signal from a transmitter is transmitted into space. This transmission is then picked up by the satellite receiver dish that is orbiting thousands of kilometres above the Earth. The satellite transmits the signal back to Earth where it’s received by a satellite dish
what other than satellite TV uses microwaves?
mobile phones, they travel as microwaves from your phone do the nearest transmitter
what is also something else that is not a satellite TV or a mobile phone that uses microwaves?
microwaves are also used for cooking.
explain how microwaves are used for cooking
they are absorbed by water molecules in the food. They penetrate a few centimetres into the food before being absorbed. The energy is then conduced or converted to other parts of the food
what is infrared radiation also known as?
heat radiation
infrared radiation is used for what?
it is used for heating and to monitor temperature
why do electrical heaters radiate IR (infrared radiation)?
they radiate IR to keep us warm. Also grills use IR to cook food
what objects give out IR?
all objects. However, the hotter the object, the more IR radiation it gives out
how can infrared radiation given out by objects be detected?
it can be detected in the dark of the night by night-vision equipment
how does night-vision equipment work?
it turns into an electrical signal, which is displayed on a screen as a picture allowing things which would otherwise be hidden in the dark to be seen.
In what other cases can visible light be useful?
it can be used for communication using optical fibres
what do optical fibres do?
they carry data over long distances as pulses of light
how do optical fibres work?
They work by bouncing waves off the sides of a very narrow core. The pulse of light enters the fibre at a certain angle at one end and is reflected again and again until it emerges at the other end
when are optical fibres used?
they are used for telephones and broadband internet cables. They are also used for medical purposes to see the ‘inside’ of. the body without having to operate
what other than for communication is visible light used for?
photography
why is visible light used for photography?
cameras use lens to focus visible light onto a light-sensitive film or sensor
what does the lens aperture of a camera control?
how much light enters the camera
what does the shutter speed of a camera determine?
how long the film or sensor is exposed to the light
what is the photographer able to do by varying the shutter speed and aperture of a camera?
the photographer will be able to capture as much or as little light as they want in their photograph
what is ultraviolet used for?
used in fluorescent lamps
what is fluorescence used for?
it is used for a property of certain chemicals where ultraviolet radiation (UV) is absorbed and then visible light is emitted.
fun fact: that is why fluorescent colours looks so bright, it is because they actually emit light
Fluorescent lights use UV radiation for what?
they use it to emit visible light
why in some way are fluorescent lights better than filament light bulbs?
they are more energy efficient
what are x-rays used for?
to view the internal structure of objects and materials, including our bodies. That is why they are so useful in medicine
how are x-ray images made?
x-rays are directed through the object or body onto a detector plate. The brighter bits are where fewer x-rays get through
what do x-rays pass easily through?
x-rays pass easily through flesh but not through denser materials like bones or metal
what can exposure to x-rays can cause?
it can cause mutations that lead to cancer.
that is why Radiographers and patients are protected as much as possible by lead aprons and shields and exposure to the radiation is kept to a minimum
what is the name of people who run x-ray tests on a hospital?
radiographers
what can gamma radiation be useful for?
- sterilising medical equipment
- sterilising food
why is it better to use gamma radiation to sterilise medical equipments?
because trying to boil plastic instruments can damage the equipment, while gamma radiation doesn’t
how does gamma radiation sterilise medical equipment and food?
it sterilises by killing all the microbes
why does food need to be sterilised?
it needs to be sterilised to keep food fresh for longer, without having to freeze it, cook it or preserve it in some other way
is it safe to sterilise food with gamma radiation?
yes because the food is not radioactive afterwards, so it is perfectly safe to eat it.
some EM radiation mostly passes through what?
through soft tissue without being absorbed
some radiations can cause what in living cells?
can cause cancerous changes
what happens if radiation is absorbed?
it causes heating of the cells
what happens if EM radiation enters living tissues?
it is often harmless, but sometimes it creates havoc
what do the effects of EM radiation depend on?
on it’s frequency
what is the problem with a high frequency EM radiation?
the more energy it has the more harmful it can be.
are lower frequencies harmful?
as far as we know, it is less harmful than high frequency waves
how is the body affected if exposed to too much of microwaves?
it heats up molecules inside things, so microwaves heat human body tissue internally
what is the reason for why microwaves are dangerous?
microwaves have similar frequency to the vibrations of many molecules, so they can increase these vibrations. The result is internal
how can we make microwaves less dangerous?
microwave ovens need to have shielding to prevent microwaves from reaching the user.
how is the body affected if exposed to too much of infrared?
the infrared range of frequencies can make the surface molecules of any substance vibrate (like microwaves), this has a heating effect. It can cause nasty skin burns
how can we make infrared waves less dangerous?
you can protect yourself using insulating material to reduce the amount of IR reaching your skin
how is the body affected if exposed to too much of ultraviolet?
it can damage surface cells and cause blindness
what is the reason for why ultraviolet are dangerous?
some frequencies of UV radiation are ionising - they carry enough energy to knock electrons off atoms: This can cause cell mutation or destruction and cancer
how can we make ultra violet waves less dangerous?
you should wear sunscreen with UV filters whenever you’re out in the sun and stay out of strong sunlight to protect you skin from UV radiation
how is the body affected if exposed to too much of gamma radiation?
it can cause cell mutation or destruction leading to tissue damage or cancer.
what is the reason for why gamma radiation to be dangerous?
very high-frequency waves such as gamma rays are ionising, and carry much more energy than UV rays. This means they can be much more damaging and can penetrate further into the body
how can we make gamma waves less dangerous?
gamma rays should be kept in lead-lined boxes when not in use. Also, if needed to be exposed to it, exposure time should be as short as possible
what type of wave is visible light?
it is a traverse wave, like all EM waves
reflection of visible light allow us to do what?
to see most objects because light bounces off them into your eyes
what happens when light reflects from an uneven surface (eg. a piece of paper)?
the light reflects from an uneven surface the light reflects off at all different angles and you get a diffuse reflection
what happens when light reflects from an even surface (eg. smooth and shiny like a mirror)?
it’s all reflected at the same angle and you get a clear reflection
what is the law of reflection?
angle of incidence = angle of reflection
to what rays does the law of reflection apply to?
to every reflected ray
how are virtual images formed?
they are formed when the light rays bouncing off an object onto a mirror are diverging, so the light from the object appears to be coming from a completely different place
how do waves travel?
waves travel at different speeds in substances which have different densities.
how do EM waves travel?
they travel more slowly in denser media
how do sound waves travel?
they travel faster in denser substances
what happens to a wave when it crosses a boundary between two substances (eg. from glass to air)?
it changes speed
what happens to a wave that hits the boundary ‘face on’?
it slows down but carries on in the same direction
what happens to a wave that meets a different medium at an angle?
this part of the wave hits the denser layer first and while this part carries on at the first, faster speed. So the wave changes direction - its been refracted
what does a ray diagram show?
it shows the path that a wave travels
what is a great way to experiment with refraction?
1) using a light source and a rectangular block of a particular material (eg. glass) resting on top of a piece of paper
2) shine light ray at an angel into the block. Some light is reflected, but a lot of it passes through the glass and gets
