AQA Electromagnetic waves

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Which of the electromagnetic waves travels the fastest?

None. They all travel at the same speed (3 x10⁸ m/s)
Name and sequence the electromagnetic waves starting with the lowest frequency
- radio waves
- microwaves
- infrared
- visible light
- ultraviolet
- x-rays
- gamma rays
Which type(s) of electromagnetic wave do our eyes detect?

visible light (only)
Higher tier
What causes waves to refract at a media boundary?

Change of velocity
Higher tier
Why does a wave change direction when it slows down as it enters a medium at an angle?
- Different parts of a wave front enter the medium at different times and hence slow down at different times. This causes the wave front to change direction.
Higher tier
How are radio waves produced?

By oscillations in electrical circuits
Higher tier
What can happen when radio waves are absorbed?

They can create an alternating current with the same frequency as the radio wave, so can produce oscillations in an electrical circuit.
Where do gamma rays originate from?

Changes in the nuclei of atoms
Which three types of electromagnetic radiation can have hazardous effects on human body tissue?
- Ultraviolet
- X-rays
- Gamma rays
Radiation dose is measured in Sieverts (Sv).
What does it measure
and
what does it depend upon?
- The risk of harm resulting from exposure to radiation.
- It depends upon the type of radiation and the size of the dose
State two ways in which ultraviolet waves are damaging?
- Cause skin to age prematurely
- Increase the risk of skin cancer
Which two types of electromagnetic radiation are ionising and can cause the mutation of genes and cancer?
- X-rays
- Gamma rays
(as these are the highest frequency and hence transfer the most energy)
State some uses for radio waves
- Communication eg
- - TV
- - radio
State some uses for microwaves
- satellite communications
- cooking food
(microwaves are able to penetrate the Earth's atmosphere so are used in all satellite communication)
State some uses of infrared radiation
- electrical heaters
- cooking food
- infrared cameras / thermal imaging
State some uses of visible light
- fibre optic communications
- photography
State some uses of ultraviolet light
- energy efficient lamps
- sun tanning
- security markings
State some uses of x-rays
- medical imaging (eg scanning broken bones)
- security screening (eg bags at airports)
State some uses of gamma rays
- medical imaging
- treatment of some cancers
- sterilisation (of some foods and equipment)
What is the name given to the place at which a converging lens brings together parallel beams of light?

principal focus (or focal point)
What is the name given to the distance between the lens and the principal focus?

focal length
What is a real image?

An image that can be projected onto a screen
What is a virtual image?

An image that cannot be projected onto a screen
The image produced by a convex lens...
- A) Can be virtual or real
- (Depending upon where the object is in relation to the lens)
What type of lens is this?
- Convex (shape)
- Converging (action)
What type of lens is this?
- Concave (shape)
- Diverging (action)
What is the unit for magnification?

It doesn't have one (as it is a ratio)
What type of image is always produced by a concave lens?

virtual
What is the correct term for reflection from a smooth surface?

specular reflection
Reflection from a rough surface causes scattering. Name this type of reflection.

Diffuse reflection
If an object looks red in white light, what colours of light is it absorbing?

Everything other than red
If an opaque object appears blue it only reflects blue light. What happens to the other frequencies of visible light?

They are absorbed by the object
In an opaque object reflects all wavelengths of light, what colour does it appear?

white
What name is given to materials that transmit light clearly with no scattering?

Transparent
What name is given to materials that scatter light when transmitting it?

Translucent
What name is given to materials that do not transmit light?

Opaque
How does temperature affect the amount of infrared radiation a body emits?

The higher the temperature, the greater the amount emitted.
What is a 'perfect black body'

A body that absorbs all radiation incident on it
Is a black body:
a) only a good emitter of radiation
a) only a good absorber of radiation
c) both a good emitter and absorber of radiation

c) both a good emitter and absorber of radiation
Higher only
If a body absorbs radiation faster than it emits it, what happens to its temperature?

In increases
Higher only
If a body is at a constant temperature what can you say about the amount of radiation emitted and absorbed?
They are equal.
- Remember that they are always emitting AND absorbing