Waves Flashcards
What do waves transfer
- energy
- in the direction they are travelling
What happens when waves travel through a medium
- The particles of the medium oscillate and transfer energy between each other
- but overall the particles stay in the same place — only energy is transfered
What is the amplitude of a wave
- the maximum displacement of a point on the wave from its undisturbed position
What is the wavelength of a wave
- the distance between the same point on two adjacent waves
- (e.g. between the trough of one wave and the trough of the wave next to it)
What is the frequency of a wave
- The number of complete waves passing a certain point per second
What is frequency measured in
- hertz (Hz)
- 1 Hz is 1 wave per second
What is the period of the wave
- the amount of time it takes for a full cycle of the wave to pass a point
Describe a transverse wave
oscillates perpendicular (at 90’) to the direction of energy
Give some examples of transverse waves
- All electromagnetic waves; e.g. light
- Ripples and waves in water
- Guitar strings
Describe longitudinal waves
- the oscillations are parallel to the direction of energy transfer
Give examples of longitudinal waves
- sound waves in air
- ultrasounds
- shock waves; e.g. some seismic waves
What is the wave speed
The speed at which energy is being transferred (or the speed the wave is moving at)
What do you use to measure the speed of sound
Oscilloscope
How do you use an oscilloscope
- By attaching a signal generator to a speaker you can generate sounds with a specific frequency
- you can use 2 microphones and an oscilloscope to find the wavelength of the sound waves generated
What happened when a wave arrives at a boundary between 2 different materials
They can be:
- absorbed
- transmitted
- Reflected
What happens when a wave is absorbed by the second material
- it transfers energy to the material’s energy stores
- Often, the energy is transferred to a thermal energy store, which leads to heating
What happens when a wave is transmitted through the second material
- the waves carry on travelling through the new material
- this leads to refraction
What can rarefraction be used for
- in communications
- the lenses of glasses and cameras
What happens when a wave is reflected from the second material
- the incoming wave is neither absorbed nor transmitted
- but instead ‘sent back’ away from the second material
What contributes to what happens when a wave arrives at a boundary between 2 materials
- the properties of the materials involved
- the wavelength of the wave
Describe the process of rarefraction
- wave crosses a boundary between 2 materials = changes speed
- if wave is travelling along the normal it will change speed, but not be rarefracted
- if the wave hits at an angle, it changes direction (rarefraction)
- the wave bends towards the normal if it slows down and away the normal if it speeds up
What is the optical density of a material
- a measure of how quickly light can travel through it — the higher the optical density, the slower light waves travels through it
What happens to the wavelength and frequency of a wave when it’s rarefracted
- the wavelength changes
- the frequency stays the same
What are rays
- straight lines that are perpendicular to wave fronts
- showing direction a wave is travelling in
What are electromagnetic waves
- transverse waves
- made up of oscillating electric and magnetic fields
- transfer energy from the source of the waves to an absorber.
How do we remember the different types of electromagnetic waves
- Red
- Mice
- Playing
- In
- Very
- Unusual
- X-ray
- games
What does red mice playing in very unusual x ray games stand for
- Radio waves
- Micro waves
- infra red
- visible light
- ultraviolet
- x-rays
- Gamma rays
What part of the electro magnetic spectrum can our eyes see
- the visible light section
What can affect the speed of an EM wave
The type of material it travels through (which can lead to refraction)
What are alternating currents made up of
- oscillating charges
- As the charges oscillate, they produce oscillating electric and magnetic fields
- i.e. electromagnetic waves
How can you produce radio waves
- using an alternating current in an electrical circuit
- Using a transmitter the charges will then oscillate, producing the radio wave
What happens when the transmitted radio waves reach a receiver
- they are absorbed
- energy is transferred from electrons of the material of the receiver
- this causes the electrons to oscillate and produce an alternating current
What controls the frequency of the current in a circuit
- the radio waves that generated the current
What are radio waves
EM radiation with wavelengths longer than about 10 cm
What can radio waves be used for
- communication
- TV
- Bluetooth
Why can radio waves be used for communication
- Long-wave radio waves (1-10km)
- cab diffract around the curved surface when transmitted
- making it possible for radio signals to be received, even if the receiver isn’t in line of the the sight if the transmitter
How are shortwave radio waves received at long distances
They are reflected form the ionosphere (an electrically charged layer in the Earth’s upper atmosphere
——> this is how Bluetooth works
——> happens at distances of (10m - 100m)
How do medium-wave signals carry transmissions
- same as short wave-length radio waves do
Why uses short-wave radio waves
- some transmissions need to be shorter
- to get reception, you must be in direct sight of the transmitter
What are microwaves used for
- satellites for communication
- Microwave ovens
Why are microwaves used in satellite communication
They can pass easily through the Earth’s watery atmosphere
How are microwaves used in satellite communication
- the signal from a transmitter is transmitted into space
- it’s picked up by the satellite receiver dish orbiting above the Earth
- the satellite transmits the signal back to Earth in a different direction
- where it’s received by a satellite dish on the ground
How are microwaves used in microwave ovens
- the microwaves are absorbed by the water molecules in food
- the microwaves penetrate a few cm into the food and are then absorbed and transfer the energy they were carrying
- energy is transferred to the water molecules in the food and this causes them to heat up
- the water molecules then transfer this energy to the rest of the molecules in the food by heating — which cooks the food
What can Infraed radiation be used for
- Monitor temps
- OR increase temps
- remote controls for TVs
- cooking
How can infrared radiation monitor temps
- IR radiation os given out by all objects
- the hotter the object = the more it gives out
- IR cameras can detect this and therefore monitor temp
How to infrared cameras work
- turn IR radiation into an electrical signal
- which can be displayed on a screen as a picture
- the hotter the object = the brighter it appears
How can infrared radiation increase temps
- absorbing IR causes objects to get hotter
- Food can be cooked using IR (when food absorbs it; e.g. toasters)
- electric heaters work in the same way
How to electrical heaters work
- they contain a long piece of wire that heats up when a current flows through it
- the wire then emits lots of IR radiation (and a little visible light from the wire glowing)
- The emitted IR radiation is absorbed by objects and the air in the room’s thermal energy stores
What is reflection of a wave?
The bouncing back of a wave when it meets a surface or boundary that does not absorb it.
What is refraction of a wave?
The bending of a wave as it passes from one medium to another with a different density.
What is diffraction of a wave?
The spreading of a wave as it passes through a gap or around an obstacle.
What is interference of waves?
The combination of two or more waves to form a resultant wave with a new amplitude and wavelength.
What is the principle of superposition?
When two waves meet, the resultant displacement at any point is equal to the sum of the individual displacements at that point.
What are the uses of ultra violet radiation
- Used in tanning beds
- sterilising equipment
- fluorescent lights.
What are the uses of x-rays
- Used in medical imaging to see inside the body
- in airport security scanners.
What are the uses of Gamma rays
- Used in medical treatment of cancer,
- sterilization of medical equipment
- in scientific research.
What is the effects on your body of each type of radiation based on
How much energy the waves transfers
What is the least harmful type of wave
- low frequency waves (e.g. radio waves)
- they don’t transfer much energy
- so mostly pass through soft tissue without being absorbed
What is the most harmful type of wave
- High frequency waves (e.g. UV, X-rays, Gamma rays)
- they transfer lots of energy
- so they cause lots of damage
Why is UV radiation dangerous
- It damages surface cells, which can lead to sunburn and cause skin to age prematurely
- some more serious effects: blindness, increased risk of cancer
Why are X-rays and gamma rays dangerous
- they are ionising radiation
- this means they carry enough energy to knock electrons off atoms
- this can cause gene mutations or cell destruction or cancer
How can you measure risk of the radiation dose
In Siverts
—> total amount of radiation absorbed and type of radiation absorbed
Which objects absorb and which emit infrared radiation
ALL OBJECTS
—> all are continuously emitting and absorbing IR radiation
Where on the object is IR radiation emitted
The surface
What cause an object to emit more or less radiation
The hotter = the more it radiates in a given time
What happens when an object emits IR radiation
It starts to then cool down
What does the levels of emitting IR radiation depend on in it’s surroundings
- when it’s hotter than its surroundings = emits more IR radiation than it absorbs
- when it’s cooler than it’s surroundings - absorbs more IR radiation than it emits
What rate does objects at a constant temp absorb and emit radiation
- the same rate as each other
Which colours and surfaces emit and absorb radiation better than others
- black is better at absorbing and emitting radiation than white
- A Matt surface is better at absorbing and emitting radiation than a shiny one
