P6 - Waves Flashcards
What do aves transfer
Transfer energy in the direction they’re travelling
What happens when a wave travels through a medium
The particles of the medium oscillate and transfer energy between each other. Particles stay in the same place, only energy is transferred
What’s the amplitude of a wave
Maximum displacement of a point on the wave from its undisturbed position.
What’s the wavelength of a wave
Distance between two adjacent waves
Frequency of waves
Number of complete waves passing a certain point per second
1hertz is 1 wave per second
Period = 1/frequency
What vibrations do transverse waves have
Sideways vibrations
Key information of transverse waves
Oscillations are perpendicular to the direction of energy transfer Most waves are transverse All EM waves Ripples and waves in water Wave in a string
What vibrations do longitudinal waves have
Parallel vibrations
Key information of longitudinal waves
Oscillations are parallel to the direction of energy transfer
E.g sound waves in air
- What do you use to measure the speed of sound
- What do you use to measure speed of water ripples
- What do you use to measure waves on a string
- Oscilloscope
- Ripple tank
- Wave equation
What happens if when a wave meets a boundary between two materials and why?
Either three things
Wave is absorbed by second material
Wave is transmitted through second material
Wave is reflected
What happens depends on wavelength, material properties
What happens when the wave is absorbed by the second material
Wave transfers energy to materials energy stores (normally thermal )
What happens when a wave is transmitted through the second material
Wave carries on traveling through new material and often leads to refraction. This is used in communication as well as glasses and cameras
What happens if the wave is reflected
Incoming ray is sent back (how echos are made)
Example of transferring energy to an absorbed
Camp fire transfers infrared radiation to surroundings. This infrared is absorbed by objects and transfers energy to objects thermal, energy stores
All EM waves travel the same speed through
The air or a vacuum
What are electromagnetic waves
Vibrations of electric and magnetic fields
What speeds to the em waves vary through
10^-15 to 10^4
List the EM waves in order and their wavelengths and properties
Radio waves(10^4) microwaves(10^-2) infrared radiation(10^-5) visible light(10^-7) ultra violet(10^-8) x-rays(10^-10) gamma rays(10^-15) Radio waves are the longest wavelength but the lowest frequency (carries on as a sequence going down the waves)
What happens when a wave crosses a boundary between 2 materials
It changes speeds
What happen if wave is travelling along the normal when it crosses a boundary
Changes speed but isn’t refracted
What happens if the wave hits the boundary at an angle
It’d refracted. Bends towards normal if it slows down, bends away from normal if it speeds up. How much it’s refracted depends on wave speed and materials density
Higher density = slower light waves travel (bend towards normal)
Wavelength changes when refracted
What is optical density of a material
A measure of how quickly light can travel through it
What are rays
Rays are straight lines that are perpendicular to wave fronts (show wave direction)
- Draw boundary and normal
- Draw incident ray (first ray)
- Draw refracted ray (second ray)
What is a wave front
Line showing all points on a way that are in the same position as each other after a given number of wavelengths
When wave crosses boundary at an angle, only part of the front crosses boundary first
If new material is dense = travels slower
What are EM waves made up of
Oscillating electric and magnetic fields
What are alternating currents made up of
Oscillating charges. As the charges oscillate they make EM waves
Frequency of wave produced will be equal to the frequency of the Alternate current
How are radio waves produced
Use an alternate current in an electrical circuit.
Object in which charges oscillate in to create radio waves in an transmitter
Energy carried by waves transferred to electrons in the material of receiver
Energy causes electrons to oscillate ans generate alternate current
Current has same frequency of radio waves produced
What are radio waves used for
Used for communication.
Long radio waves transmitted from London to halfway round the world. Wavelengths refract and bend around the surface of earth
Short wave radio signals received at long distances as they’re reflected off ionosphere
Blue tooth uses short RW to send data
RW for tv and radio are short
What are micro waves used for
Communicate to and from satellites
Need to use micro waves as they pass easily through the watery atmosphere
Satellite Tv get signal from transmitter transmitted into space. Picked up by satellite receiver dish which transmits a signs in a different direction back to earth which is received by satellite dish on ground.
There’s a time delay due to distance
How are micro waves used in microwave ovens
Micro waves to be absorbed by water molecules in food (different wave length)
MW penetrate few cm Into food before being absorbed and transfer energy to water molecules in food to heat up
Watermolecules transfer energy to rest of molecules to heat up
What is infrared radiation used for
Infrared radiation is given out by all objects
Infrared cameras are used to detect infrared radiation and monitor temperatures. They detect IR and turn it into an electric signal which is displayed on a screen hotter = brighter
Absorbing IR causes objects to heat
Used in electric heaters as they contain a long wire that emits IR which is absorbed by objects and air in the room and transfers energy to thermal energy stores
Visible light uses
Lights
Optic fibres are thin glass or plastic fibres that carry data over long distances as pulses of visible light which work because of reflection
Light rays bounced back and forth until they reach end of fibre
VS used in optic fibres as light is easily refracted enough and not easily absorbed or scattered.
Uses of ultra violet
Suntans (UV lamps)
UV produced by sun
Fluorescent lights generate UV which is absorbed and emitted as visible light
Uses of x rays and gamma rays
X rays easily pass through flesh but not denser materials like bones
Radio graphics use both to treat cancer - carefully directed to kill cancer cells
Dangers of EM waves
High frequency waves like UV and X-rays and gamma transfer lots of energy and can deal lots of damage
UV damages surface cells - sunburn , skin to age prematurely + skin cancer risk
X rays and gamma rays types of ionising radiation - gene mutation or cell destruction and cancer
