what do waves have?
1) Wavelength (lambda sign) is the distance from one peak to the next.
2) frequency(f) is how many complete waves there are per second(passing a certain point) it is measured in hertz(Hz). 1Hz is 1 wave per second.
3) Amplitude is the height of the wave (from rest /equilibrium to crest)
4) the speed (v, for velocity)is , well , how fast the wave goes.
5) The period (T) is the time it takes (in seconds) for one complete wave to pass a point.
Equation for wave frequency?
Frequency (f) = 1 .
Equation for wave speed?
Wave speed = frequency x wavelength
(m/s) (Hz) (m)
What is a transverse wave?
Most waves are transverse waves.
In transverse waves the vibrations are at 90 degree to the direction energy is transferred by the wave
1) light and all other EM waves
2) a slinky wiggled up and down
3) waves on strings
4) ripples on water
What is a longitudinal wave?
A wave where vibrations occur parallel to the direction the wave is travelling
example of longitudinal waves?
1) sounds waves
2) ultra sound
3) shock waves e.g sesmic waves
4) a slinky spring, when you push the waves
what do you waves tranfer?
energy and information but not matter
give an example of wave transfering energy?
all waves carry and transfer energy in the direction they are traveling.
eg microwaves in the oven that makes things warm up - their energy is transferred to food you’re cooking.
sound waves can things vibrate or move, e.g loud bangs can start avalanches
give an example of wave transfering information?
Waves can also be used as signals to transfer information from one place to another — e.g. light in optical fibres, or radio waves travelling through the air.
What is Wavefronts?
Two or more waves moving together in same direction have wavefronts
A horizontal line drawn linking all the peaks in a set of waves
Wavefronts are imaginary planes that cut across all the waves, connecting the points on adjacent waves which are vibrating together.
The distance between each wavefront is equal to one wavelength, i.e. each wavefront is at the same point in the cycle.
What is the Doppler effect?
The change in frequency and wavelength caused by relative movement of the source of
wave or observer
Give an example of the Doppler effect in sound waves?
- When an ambulance goes past you the siren decreases in pitch
- This is because the wavelength of the sound waves increases
1) If a wave source is moving towards an observer, the frequency of the wave they observe will be higher and the wavelength will be shorter than the original wave emitted by the source.
2) If a wave source is moving away from an observer, the frequency of the wave they observe will be lower and the wavelength will be longer than the original wave emitted by the source.
3) This is because the wave’s speed is constant — if the source is moving, it ‘catches up’ to the waves in front of it. This causes the wavefronts to bunch up in front of the moving source and spread out behind it.
How many Electromagnetic(EM) wave are there?
there are 7 types of EM waves
name the 7 types of electromagnetics (EM) waves, from longest to shortest waveslenghts?
ultra - violet
what type of waves are EM
they are transverse waves
Do EM waves transfer energy?
yes they do
can EM waves be reflected and refracted?
yes they can
Do EM waves travel at the same speed?
they travel at the same speed through free space(a vacuum).
do the different colours of visible light have the same wave lenght?
no, red has the longest wave lenght and lowest frequency and violet has the shortest wave lenght and highest frequency.
what are radio waves mainly used for?
Radio waves are mainly used for communications
are radio waves shorter than 10 cm?
no, they are longer than 10cm
how long are long radio waves and how are they transmitted?
they are 1- 10km,
long radio waves can be transmitted a long way because long wave lengths are bent around the curved surface of the earth
how short are short radio waves and how are they transmitted?
about 10m - 100m.
short radio waves can transmitted long distance via a transmitter. Thats because they are reflected from the ionosphere(a layer of the earths atmosphere)
how long are radio waves for tv and FM broadcasting
they have short wavelenghts 10cm - 10m.
To get reception, you must be in direct sight of the transmitter — the signal doesn’t bend around hills.
what are micro waves used for?
satellite communication and cooking
what is the length of micro waves?
1 - 10 cm
example of uses for micro waves?
2) Satellite communication (including satellite TV signals and satellite phones) uses microwaves. 3) For satellite TV, the signal from a transmitter is transmitted into space, where it’s picked up by the satellite receiver dish orbiting thousands of kilometres above the Earth. The satellite transmits the signal back to Earth where it’s received by a satellite dish on the ground. 4) Mobile phone calls also travel as microwaves from your phone to the nearest transmitter. 5) Microwaves are also used for cooking. These microwaves are absorbed by the water molecules in the food. They penetrate a few centimetres into the food before being absorbed. The energy is then conducted or convected to other parts (see pages 82-83) of the food.
what is infrared radiation used for?
1) Infrared radiation (or IR) is also known as heat radiation. Electrical heaters radiate IR to keep us warm, and things like grills use IR to cook food.
2) IR is given out by all objects — the hotter the object, the more IR radiation it gives out.
3) The infrared radiation given out by objects can be detected in the dark of night by night-vision equipment. The equipment turns it into an electrical signal, which is displayed on a screen as a picture, allowing things which would otherwise be hidden in the dark (e.g. criminals on the run) to be seen.
can light signals travel through optical fibres?
if so expalin how
1) As well as using it to look at things around us, visible light can be used for communication using optical fibres — which carry data over long distances as pulses of light.
2) Optical fibres work by bouncing waves off the sides of a very narrow core.
3) 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.
4) Optical fibres are increasingly being used for telephone and broadband internet cables. They’re also used for medical purposes to ‘see inside’ the body without having to operate.
how is visible light used for photography?
It sounds pretty obvious, but photography would be tricky without visible light.
1) Cameras use a lens to focus visible light onto a light-sensitive film or sensor.
2) The lens aperture controls how much light enters the camera.
3) The shutter speed determines how long the film or sensor is exposed to the light.
4) By varying the aperture and shutter speed (and also the sensitivity of the film or the sensor), a photographer can capture as much or as little light as they want in their photograph.
how is ultraviolet used in fluorescent lamps?
1) Fluorescence is a property of certain chemicals, where ultraviolet radiation (UV) is absorbed and then visible light is emitted. That’s why fluorescent colours look so bright — they actually emit light.
2) Fluorescent lights (like the ones you might have in your classroom) use UV radiation to emit visible light. They’re safe to use as nearly all the UV radiation is absorbed by a phosphor coating on the inside of the glass which emits visible light instead. 3) Fluorescent lights are more energy-efficient (see page 76) than filament light bulbs.
how are x-rays used?
1) X-rays are used to view the internal structure of objects and materials, including our bodies — which is why they’re so useful in medicine.
2) To make an X-ray image, X-rays are directed through the object or body onto a detector plate. The brighter bits are where fewer X-rays get through. This is a negative image.
3) Radiographers in hospitals take X-ray photographs to help doctors diagnose broken bones — X-rays pass easily through flesh but not through denser material like bones or metal.
4) Exposure to X-rays can cause mutations that lead to cancer. Radiographers and patients are protected as much as possible by lead aprons and shields and exposure to the radiation is kept to a minimum.
name useful uses for Gamma Radiation?
sterilising medical equipment
1) Gamma rays are used to sterilise medical instruments by killing all the microbes.
2) This is better than trying to boil plastic instruments, which might be damaged by high temperatures.
1) Food can be sterilised in the same way as medical instruments — again killing all the microbes.
2) This keeps the food fresh for longer, without having to freeze it, cook it or preserve it some other way.
3) The food is not radioactive afterwards, so it’s perfectly safe to eat.
can EM radiation be harmful to people?
When EM radiation enters living tissue — like you — it’s often harmless, but sometimes it creates havoc.
1) Some EM radiation mostly passes through soft tissue without being absorbed — e.g. radio waves.
2) Other types of radiation are absorbed and cause heating of the cells — e.g. microwaves.
3) Some radiations can cause cancerous changes in living cells — e.g. gamma rays can cause cancer.
are higher frequency EM radiation more dangerous or lower frequency EM radiation?
higer frequency EM radiation is more dangerous
1) The effects of EM radiation depend on its frequency. The higher the frequency of EM radiation, the more energy it has and generally the more harmful it can be.
2) In general, waves with lower frequencies (like radio waves — which are harmless as far as we know) are less harmful than high frequency waves like X-rays and gamma rays.
3) From a safety point of view, it’s how radiation affects human tissue that’s most vital. You need to know how the body can be affected if exposed to too much of the following radiation:
Name the increasing freqency EM radiation in order ?
also their dangers and ways to protect against the dangers
1) Microwaves have a similar frequency to the vibrations of many molecules, and so they can increase these vibrations. The result is internal heating — the heating of molecules inside things (as in microwave ovens). Microwaves heat human body tissue internally in this way.
2) Microwave ovens need to have shielding to prevent microwaves from reaching the user.
1) The infrared (IR) range of frequencies can make the surface molecules of any substance vibrate — and like microwaves, this has a heating effect. But infrared has a higher frequency, so it carries more energy than microwave radiation. If the human body is exposed to too much infrared radiation, it can cause some nasty skin burns.
2) You can protect yourself using insulating materials to reduce the amount of IR reaching your skin.
1) UV radiation can damage surface cells and cause blindness. 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.
2) You should wear sunscreen with UV filters whenever you’re out in the sun, and stay out of strong sunlight to protect your skin from UV radiation.
1) Very high-frequency waves, such as gamma rays, are also ionising, and carry much more energy than UV rays. This means they can be much more damaging and they can penetrate further into the body. Like all ionising radiation, they can cause cell mutation or destruction, leading to tissue damage or cancer.
2) Radioactive sources of gamma rays should be kept in lead-lined boxes when not in use. When people need to be exposed to them, e.g. in medical treatment, the exposure time should be as short as possible.