# Physics P6

• Created by: abbiedye
• Created on: 29-07-18 20:44

## What are transverse waves?

• In transverse waves, the oscillations (vibrations) are perpendicular to the direction of energy transfer
• Include: all electromagnetic waves (light), ripples and waves in water, and a wave on a string
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## What are longitudinal waves?

• In longitudinal waves, the oscillations are parallel to the direction of the energy transfer
• Sound waves in air
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## How do you calculate wave speed?

• The speed at which energy is being transferred
• wave speed = frequency x wave length
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## When a wave meets a boundary

Three things can happen

• The wave is absorbed by the second material
• The wave is transmitted through the second material
• The wave is reflected
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## What are electromagnetic (EM) waves?

• Transverse waves
• Travel at the same speed through air or a vacuum (space)
• They vary in wavelength from around 10^-15 m to more than 10^4m
• We group them based on their wavelength and frequency
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## What is the spectrum of waves?

• Radio waves - 1m to 10^4m
• Microwaves - 10^-2m
• Infrared - 10^-5m
• Visible Light - 10^-7m
• Ultra violet - 10^-8m
• X-rays - 10^-10m
• Gamma rays - 10^-15m

DIFFERENT PROPERTIES

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## What is refraction?

• Refraction = waves changing direction
• Ray diagrams show the path of a wave
• You can also explain refraction using wavefront diagrams
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• EM waves are made up of oscillating electric and magnetic fields
• Alternating currents (ac) are made up of oscillating charges. As the charges oscillate, they produce oscillating electric and magnetic fields i.e electromagnetic waves
• Radio waves - ac in an electrical circuit
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## How are radio waves used for communication?

• Long-wave radio - can be transmitted halfway round the world
• Bluetooth - short distances
• Medium - waves
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## What are the uses of microwaves?

• Satellites - signals from a transmitter to a satellite, sent and received from a long distance
• Microwaves ovens - microwaves need to be absorbed by water molecules, microwaves penetrate a few cms into food before being absorbed
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## What can infrared radiation be used for?

• Infrared cameras - detect radiation and monitor temperature
• Absorbing IR radiation causes objects to get hotter - food can be cooked
• Electric heaters work in the same way
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## What are more uses of EM waves?

• Fibre optic cables use visible light to transmit data
• Ultraviolet radiation gives you a suntan
• X-rays and gamma rays are used in medicine - x-rays and treating cancer
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## How can you investigate infrared radiation?

• You can investigate emission with a Leslie cube
• You can investigate absorption with the melting wax trick
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## Why are some EM radiation sources harmful?

• Low frequency - don't transfer much energy and pass through tissue
• High frequency - transfer lots of energy and cause a lot of damage
• UV radiation - damages surface cells and skin cancer
• X-rays and gamma rays - ionising and gene mutation and destruction
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## How can you measure risk of radiation?

• Measured in the radiation dose sieverts
• It measures the risk of harm from the body being exposed to radiation
• It is not a measure of the amount of radiation that has been absorbed - risk = amount and how harmful
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