P12 Revision Flashcards
The electromagnetic spectrum(in order of decreasing wavelength
and increasing frequency and energy) is made up of:
1)Radio waves
2) Microwaves
3) Infrared radiation
4) Visible light(red to violet)
5) Ultraviolet waves
6)X-rays and gamma rays
Wave speed(m/s)=
Frequency(HZ) x wavelength(m)
What are electromagnetic waves?
Electromagnetic waves are electric and magnetic disturbances that can be used to transfer energy from a source to an absorber
What is the speed of electromagnetic waves
300 million m/s
White light
Light from ordinary lamps and from the Sun, with all the colours of the visible spectrum in it. The wavelength increases across the spectrum going from violet to red. You can see the colours of the spectrum when looking at a rainbow and if you use a glass prism to split a beam of white light.
Examples of uses of light waves
1) In a film camera, the light is focused by the camera lens onto a light-sensitive film. The film then needs to be developed to see the image of the objects that were photographed.
2) In a digital camera or a mobile phone camera, the light is focused by the lens onto a sensor, which is made up of tiny light-sensitive cells called pixels, which give a dot of the image on a small screen at the back of a camera. After a photograph, the image’s stored electronically on a memory card.
Infrared radiation waves.
All objects emit infrared radiation and the hotter an object is, the more infrared radiation it emits. Infrared radiation is absorbed by your skin and damages/burns/lills skin cells as it heats up the cells.
Examples of infrared devices(name 3)
Optical fibres
Remote control handsets for TV and video equipment
Infrared scanners(in medicine)
Infrared cameras
Electric heaters
Electric cookers
How do optical fibres work?
Optical fibres in communications systems at times use infrared radiation instead of visible light to transmit signals from thin glass fibres, because infrared radiation is absorbed less than visible light in glass fibres. The light rays can’t escape from the fibre and when they reach the fibre’s surface, they’re reflected back into the fibre. Optical fibres are thin, transparent fibres.
How do remote control handsets use infrared radiation?
When you press a button on the handset, it sends out a sequence of
infrared pulses, these can easily be produced and detected electronically.
How do infrared scanners use infrared radiation?
Infrared scanners detect infrared radiation emitted from hot spots
on the body surface, which show the tissue underneath is unhealthy.
How do electric heaters emit infrared radiation?
Electric heaters that emit infrared radiation warm rooms quickly.
How do electric cookers emit infrared radiation?
Electric cookers with halogen hobs heat up food faster than ordinary hobs as halogen hobs are designed to emit more infrared radiation than ordinary hobs.
Absorption and emission of infrared radiation(required practical).
1) You need a thermometer and two cans of hot water, with the surface of one can light in colour and shiny, but the other with a dark, matt surface.
2) To compare absorption by two different surfaces, measure how fast the two cans containing cold water heat up when placed in sunlight for the same time. Use a thermometer to measure water temperature intervals as it cools.
3) At the start of each test, the volume and temperature of water in each can must be the same.
4)Safety: Take care with hot water
Uses of microwaves
People use microwaves for satellite communications and mobile phone signals as microwaves can pass through the atmosphere and reach satellites above the Earth. They are used for satellite TV signals.
Microwave ovens heat food faster than ordinary ovens as microwaves can penetrate into food and are absorbed by the water molecules in the food, heating it.
Similarities of microwaves and radio waves
They’re hazardous since they penetrate people’s bodies and heat the internal parts
Can be reflected
Can be refracted
Radio wave uses
Carry radio, TV and mobile phone signals
Used instead of cables to connect a computer to other devices
Carrier waves
Waves used to carry any type of signal
The shorter the wavelength of the waves:
The more information they can carry
The shorter their range
The less they spread out
Purposes of microwaves and radio waves of different wavelengths
Microwaves are used for satellite communications as short-wavelength microwaves can travel between satellites in space and the ground and they spread out less than radio waves, so the signal doesn’t weaken.
Radio waves of wavelengths less than about 1 metre are used for TV broadcasting from TV masts because they can carry more information than longer radio waves.
Radio waves of wavelengths 1-100m
are used by local radio stations since their range is limited to the area round the transmitter.
Radio waves of wavelengths greater than 100m are used by national and international radio stations since they have a longer range than short-wavelength radio waves.
What is the wavelength of visible light
Just below 400nm to above 700nm
What waves can be detected by the human eye as part of visible light
Microwaves
Infrared waves
Ultraviolet waves
X-ray waves
Why do emergency services use radio waves in a wavelength range no-one else is allowed to use?
Radio waves of wavelengths from 1-100m are used by emergencyj)) services since their range is limited to the range around the transmitter
Why do mobile phones affect children’s brain?
A mobile phone sends out a radio signal when you use it and because children have thinner skulls than adults, their brains will be deeply affected by mobile phone radiation.
