# Light and the electromagnetic spectrum- CP5

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What type of waves are all electromagnetic waves?
Transverse
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What speed do electromagnetic waves travel at?
3 x 10^8 m/s. They all travel at this speed in a vacuum
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What do all electromagnetic waves transfer, and where to/from?
All electromagnetic waves transfer energy from source to observer, for example, when you warm yourself using an electric heater, infrared waves transfer energy from the thermal energy store of the heater to your thermal energy store.
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What are some differences between EM waves?
They vary in wavelength and frequency. The end of the EM spectrum has the longest wavelength and the lowest frequency and the other end has the highest frequency and the shortest wavelength.
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Name the EM wave groups in order?
Radio waves, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays
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Which is the only group the human eye can detect?
Visible light contains the limited range of frequencies that can be detected by the human eye.
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What happens with regards to the potential danger as the EM wave frequency increases?
As the frequency of the EM waves increases, they become progressively more dangerous. The behaviour of an EM wave in a substance depends on its frequency. The differing frequencies make the EM wave groups suitable for different uses.
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What are the uses of radio waves?
Used for communications, TV and radio and satellite transmissions.
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How are radio waves used for communications?
Low frequency so they don't cause damage if absorbed by the human body. Can be produced by oscillations in electrical circuits. When radio waves are absorbed by a conductor, they create an alternating current.
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What are the uses of microwaves?
Used for cooking food, communications and satellite communications.
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How are microwaves used for cooking?
High frequency microwaves have frequencies which are easily absorbed by molecules in food. The internal energy of the molecules increases when they absorb microwaves, which causes heating. Microwaves pass easily through the atmosphere.
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How are microwaves used by satellites?
The signal from a transmitter is transmitted into space and picked up by the satellite receiver dish in orbit, the satellite transmits it back to earth where it's received by a dish on the ground
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Why are microwaves used by satellites?
Because they can pass easily through the Earth's watery atmosphere
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All hot objects, the hotter the object, the more IR radiation it gives out
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What are infrared cameras used for?
To detect infrared radiation and monitor temperature
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How do thermal imaging cameras work?
The camera detects the IR radiation and turns it into an electrical signal, which is displayed on the screen as an image.
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How can IR radiation be used for cooking?
Absorbing IR radiation causes objects to get hotter, so the temperature of food can increase when it absorbs IR radiation
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How can IR radiation be used for short distance communication?
TV remote controls. Optical fibres- thin fibres that carry data over long distances as pulses of IR radiation.
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How do infrared sensors in security systems work?
If a change in infrared radiation is detected, an alarm sounds or a security light turns on
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What are the uses of visible light?
Illuminating things so we can see them, cameras contain image sensors that detect visible light and generate an electrical signal that can be converted into an image.
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What is fluorescence?
A property of certain chemicals where UV radiation is absorbed and then visible light is emitted. Fluorescent lights are energy efficient
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What are the other uses of ultraviolet?
Security pens to mark property, the ink will glow under UV light but are otherwise invisible. Bank notes/passports have special markings that are only visible under UV light. Kills bacteria in water
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What are the uses of x-rays?
To view the internal structure of objects, x-ray images in hospitals to diagnose broken bones and airport security scanners to detect hidden objects that metal detectors can't
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How are x-ray images produced?
X-ray radiation is directed through the object onto a detector plate.
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What are the uses of gamma rays?
To sterilise medical instruments and food, medical imaging to detect cancer and to treat cancer, where radiation is targeted to kill cancer cells
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What are the dangers of microwaves?
Internal heating of body cells
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What are the dangers of infrared radiation?
Skin burns
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What are the dangers of ultraviolet radiation?
Damage to surface cells and eyes, leading to skin cancer and eye conditions
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What are the dangers of x-rays and gamma rays?
Mutation or damage to cells in the body
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When does the velocity of electromagnetic waves change?
When a wave is transmitted from one substance to another, and unless it reaches the second substance at a right angle, its direction will also change. How much these change depends on the wavelength of the wave.
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What happens when electromagnetic waves meet a boundary and what does it depend on?
They can be refracted, reflected, transmitted or absorbed. This depends on the material at the boundary and the wavelength of the wave.
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What can cause changes in atoms and nuclei?
Absorption of a range of radiations
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What can happen when there is a change in atoms and nuclei?
It can generate radiations over a wide frequency range
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## Other cards in this set

### Card 2

#### Front

What speed do electromagnetic waves travel at?

#### Back

3 x 10^8 m/s. They all travel at this speed in a vacuum

### Card 3

#### Front

What do all electromagnetic waves transfer, and where to/from?

### Card 4

#### Front

What are some differences between EM waves?

### Card 5

#### Front

Name the EM wave groups in order?