- 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
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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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How are radiowaves made?
- 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
- Short-wave radio - received at long distances from the transmitter
- 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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