Waves Flashcards
Define a period.
The time it takes for a wave to complete one cycle.
What may happen to the a) wave speed b) frequency and c) wavelength of a wave when the wave travels from one medium to another.
a) changes
b) always stays the same
b) changes
What moves when someone is speaking?
The voice box vibrates, producing sound waves that travel through the air.
The air does not move.
What moves when a stone is dropped into water?
Ripples are produced.
The water and the stone do not move.
On a longitudinal wave, what are compressions and rarefactions.
Compressions = areas of high pressure
Rarefactions = areas of low pressure
Define a mechanical wave.
An oscillation that has to travel through matter (medium) transferring energy from one point to another e.g. sound waves.
How may you investigate the properties of waves?
- Have two people stand 100m apart, measured using a trundle wheel.
- Have one person make a loud noise e.g. by banging together two cymbals.
- The other person starts a stopwatch when they see the other person make the noise and stop it when they hear it.
- Repeat the experiment two more times and calculate the mean.
- Use v = s / t to calculate the speed of sound in air.
How do you measure the velocity of ripples on a water surface?
- Set up a ripple tank with water to a depth of 5 cm.
- Shine a lamp on the ripple tank and get the bobber to dip in and out of the water/adjust the height of a wooden rod to just touch the water surface and turn the motor on so that low frequency waves are observed.
- Wait until the first ripple reaches the end of the tank and take a photo.
- Use a metre ruler to measure the total length of five waves and divide by the number of ripples (five) to calculate the mean wavelength.
- Count the numer of ripples that pass a point in 10 seconds (measured with a stop watch). Divide this by 10 to calculate the mean frequency.
- Calculate the wave speed using v = f λ
Define wave absorption.
The energy of the wave is transferred into energy stores within the material it travels into.
Define wave transmission.
The waves continue to move into the substance after crossing the boundary between two materials.
What causes the sensation of sound?
Sound waves cause the ear drum and then other parts of the ear (three small bones) to vibrate. These vibrations are transmitted to the cochlea, where they produce electrical signals. These are passed to the brain, which interprets them as sound.
What restricts the limits of human hearing?
The conversion of sound waves to vibrations of solids only works over a limited frequency range.
Give three uses of ultrasound.
- Imaging of foetuses
- Cleaning jewellery
- Breaking down kidney stones
When an ultrasound wave meets a boundary between two materials, it is ____.
partially reflected
How can ultrasound be used to form a medical image?
Ultraound is emitted and sent through the skin. They travel through the body and are reflected by different boundaries between tissues.
The time taken for the reflections to reach a detector can be used to determine how far away a boundary is using s = v t.
The distance is halved to find the depth.
Define sonar.
A technique using ultrasound to detect underwater objects, their distances and their directions.
How are wave fronts affected if a wave slows down when crossing a boundary?
The wave fronts become closer together.
How are wave fronts affected if a wave crosses a boundary at an angle?
One end of the wave front changes speed before the other, making the wave refract (change direction).
How can radio wabes be produced?
They can be produced by oscillations in electrical
circuits.
What happens when radio waves are absorbed by an object?
They may create an alternating current with the same frequency as the radio wave itself, so radio waves can induce oscillations in an electrical circuit.
Is energy level 2 closer or further away from the nucleus than energy level 4?
Closer to.
What is emitted when electrons in an atom move down energy levels?
Electromagnetic waves.
Define a radiation dose.
A measure of the risk of harm resulting from the body’s exposure to radiation.
What harmful effects can microwaves have on the body?
The internal heating of body cells.
What harmful effects can infrared have on the body?
Skin burns.
What harmful effects can ultraviolet have on the body?
Skin cancer (through damaging surface cells).
Eye damage leading to eye conditions.
What harmful effects can X-rays have on the body?
Mutations and damage to body cells.
What harmful effects can gamma rays have on the body?
Mutations and damage to body cells.
Give two uses of radio waves.
- Satellite communications and transmissions
- Broadcasting (TV)
Give two uses of microwaves.
- Cooking
- Satellite communications and transmissions
Give three uses of infrared radiation.
- Infrared cameras
- Cooking
- Electrical heaters
Give two uses of visible light.
- Vision
- Fibre optic cables
Give three uses of ultraviolet radiation.
- Energy-efficient lamps
- Sun tanning
- Sterilising medical equipment?
Give two uses of X-rays.
- Medical imaging
- Medical treatments
Give three uses of gamma rays.
- Medical imaging (e.g. detecting cancer)
- Medical treatments (e.g. treating cancer)
- Sterilising medical equipment
Give two reasons why radio waves are suitable for their uses.
- Can travel large distances in the air.
- Can diffract around hills - longer wavelengths can bend around obstacles to be detected.
Give one reason why microwaves are suitable for their use.
Can pass through the Earth’s atmosphere to reach satellites.
Give one reason why infrared radiation is suitable for its use.
Can be transferred fast to heat things (e.g. food and rooms).
Give one reason why visible light is suitable for its use.
Has a short(er) wavelength so can carry lots more information (due to a higher frequency, so there can be more signals in a single transmission).
Give one reason why ultraviolet radiation is suitable for its use.
It can kill bacteria.
Give one reason why X-rays are suitable for their use.
They can pass through skin and flesh without passing through less dense materials like bones.
Give one reason why gamma rays are suitable for their use.
They have a very high energy, so can kill cancer cells and bacteria.
Symbol for a concave lens.
Vertical line with inward facing arrows.
Symbol for a convex lens.
Vertical line with outward facing arrows.
Define a principal focus.
A point on the principal axis where parallel incident rays meet after reflecting (in mirrors) or refracting (in lenses).
What sort(s) of images are produced with a concave lens?
Always virtual, upright and diminished.
What sort(s) of images are produced with a convex lens?
Object at 2F:
real, inverted, same size
F ≤ object distance < 2F:
real, inverted, magnified
Object distance < F:
virtual, upright, magnified
Why are some objects transparent?
They transmit all visible light.
Why are some objects translucent?
They transmit some visible light, but the rest is reflected in different directions.
Why are some objects opaque?
They don’t transmit visible light, instead reflecting and absorbing it.
What three factors does the temperature of the Earth depend on?
- the rate of absorption of radiation
- the rate of emission of radiation
- the reflection of radiation into space
How does the intensity of wavelengths emitted by an object change as the temperature increases?
The intensity of all wavelengths increases, but shorter wavelengths increase more.
Define the peak wavelength.
The wavelength emitted with the greatest intensity.
How does the peak wavelength change as the temperature of an object increases?
The peak wavelength decreases (i.e. the peak would move left on a graph of intensity against wavelength).
