# P1.6- Electromagnetic waves

What are electromagnetic waves?
Electric and magnetic disturbances that transfer energy from one place to another
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What type of waves in the electromagnetic spectrum have the longest wavelength?
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In symbols, write down the wave speed equation
v = f × λ
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Write down the rearranged equation you would use to work out the frequency of a wave if you know its wave speed and its wavelength.
f = v / λ
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A mobile phone gives out an electromagnetic wave at a wavelength of 0.3 m, which travels at a speed of 300 m/s through the air. Calculate the frequency of this wave.
f = 300 / 0.3 = 1,000 Hz (= 1 kHz)
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What happens to the energy of a wave as you increase the frequency?
The energy increases.
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What type of electromagnetic waves carry the most energy?
Gamma rays
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What is white light?
Light from the Sun and ordinary lamps. It contains all the colour of the visible spectrum.
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Is the wavelength of red light longer or shorter than violet light?
Longer
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What are the light-sensitive cells in digital cameras called?
Pixels
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True or false: every object emits infrared radiation?
True
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What happens when infrared radiation hits the skin? Why might this be dangerous?
The skin absorbs the radiation, and it heats up. This can damage or kill skin cells.
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Because infrared radiation is absorbed less in the glass fibres
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Give two uses of microwaves in communication systems.
1) They carry satellite signals. 2) They carry mobile phone signals.
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Is the frequency of a radio wave higher or lower than a microwave?
Lower
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Which three types of signals are carried by radio waves?
1) TV 2) Radio 3) Mobile phone
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What is a Bluetooth signal?
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Why was Bluetooth set up?
To enable different electronic devices to communicate with each other
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What type of waves do we use to carry satellite TV signals?
Microwaves
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What is the main use of radio waves with a very long wavelength?
To transmit national and international radio signals
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Why are they used for this purpose?
Because they have a very long range
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What possible hazards are there when using mobile phones?
The radiation might affect the brain.
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Why does the UK government recommend that the use of mobile phones by children should be limited?
Children have thinner skulls than adults, so their brains might be more affected by the radiation.
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What kind of radiation is used to transmit signals through an optical fibre?
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Why doesn’t the radiation travelling through an optical cable escape from the sides?
The ray of light bounces off the walls of the cable.
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What is the Doppler effect?
The change in wavelength and frequency that is observed when a source of waves is moving
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When was the Doppler effect discovered?
1842
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What can be seen when a light source is red-shifted?
It appears redder.
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What term is used to describe light waves being squashed when a star is moving towards us?
Blue-shift
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How does red-shift depend on the speed of the object?
The faster the object is moving away from us, the greater the red-shift is.
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Name two discoveries that Edwin Hubble made?
1) Light from distant galaxies is red-shifted. 2) The further the galaxy is away from us, the more the light is red-shifted.
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What does this tell us about the universe?
That it is expanding
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Which two ideas does the Big Bang theory state?
1) The universe is still expanding after exploding suddenly from an initial point. 2) The universe started with the Big Bang creating space, time and matter.
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What type of radiation, evidence for the Big Bang theory, was discovered in 1965?
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When was the cosmic microwave background radiation (CMBR) created?
Just after the Big Bang
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What type of radiation was the CMBR when it was created?
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Why is the CMBR now microwave radiation?
It has stretched out as the universe has expanded.
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What form of energy do scientists think is responsible for the expansion of the universe accelerating?
Dark energy
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## Other cards in this set

### Card 2

#### Front

What type of waves in the electromagnetic spectrum have the longest wavelength?

### Card 3

#### Front

In symbols, write down the wave speed equation

### Card 4

#### Front

Write down the rearranged equation you would use to work out the frequency of a wave if you know its wave speed and its wavelength.

### Card 5

#### Front

A mobile phone gives out an electromagnetic wave at a wavelength of 0.3 m, which travels at a speed of 300 m/s through the air. Calculate the frequency of this wave.