Waves Flashcards
What is meant by the amplitude of a wave?
It is the distance from the centre of the wave to the crest or trough
What is meant by the frequency of a wave?
The number of waves generated or passing a point in 1 second
What is meant by the wavelength of a wave?
It is the distance from a point on one wave to the same point on the next
What is meant by the period of a wave?
The time it takes to generate one wave or for one wave to pass a point
Describe how to measure the speed of sound with two students using a set of cymbals, stop watch and trundle wheel
One student takes the cymbals and stands still
The other students take the stop watch and use the trundle wheel to measure a set distance away
The 1st student crashes the cymbals together once
The other students start the stop watch when they see the cymbals crash together and stop it when they hear the sound
Speed of sound is calculated by distance between the students divided by the time on the stop watch
You are 5km away from a thunder storm. What reaches you first - the thunder or the lightning? Explain your answer.
The lightning. The speed of light is faster than the speed of sound.
You are 10km from a thunder storm. You count 15 seconds between seeing the lightning and hearing the thunder. How do you calculate how far away the storm is?
Use d = vt
where v is the speed of sound and t is 15 seconds
The distance must be converted into meters
You are 10km from a thunder storm. You count 15 seconds between seeing the lightning and hearing the thunder. You repeat this after the next lightning strike, the time between the lightning and thunder is now 10 seconds. What does this tell you?
The storm has moved closer to you.
What is meant by a longitudinal wave?
A wave that vibrates along the direction of travel. In a longitudinal wave, the motion of the medium is parallel to the direction of the wave
What is meant by a transverse wave?
A wave that vibrates at 90 degrees to the direction of travel. A transverse wave is a wave in which the motion of the medium is at right angles to the direction of the wave.
What type of wave is a sound wave?
Longitudinal
What type of wave is a water wave?
Transverse
What type of wave is a microwave?
Transverse
Name a longitudinal wave
Sound
Name 3 transverse waves
Radio
Microwave
Infrared
Visible light
Ultraviolet
X-rays
Gamma rays
Water waves
Name the members of the electromagnetic spectrum, from lowest to highest frequency
Radio
Microwave
Infrared
Visible light
Ultraviolet
X-rays
Gamma radiation
State one detector of radio waves
Aerial
State one detector of microwaves
Aerial
State one detector of infrared
Photodiode
Phototransistor
Which member of the electromagnetic spectrum has the most energy
Gamma radiation
State one detector of visible light
Retina in the eye
Photographic film
State one detector of ultraviolet light
Some chemicals glow or fluoresce under it
Photocells
State one detector of X-rays
Photographic film
State one detector of gamma radiation
Photographic film
GM tube
Bubble chamber
State one source of radio waves
Transmitter
Stars
State one source of microwaves
Transmitter
Magnetron
State one source of infrared
Stars
Lamps
Flames
State one source of visible light
The sun
Light bulbs
Fire
State one source of ultraviolet light
The sun
Special lamps
State one use of radio waves
Radio/TV broadcasting
Aircraft and shipping bands
Radio waves detected from space are used by astronomers to find out what objects in space are made from
State one source of gamma radiation
Stars
Some radioactive substances (e.g. Cobalt 60)
State one source of X-rays
Stars
State one use for microwave radiation
Mobile phone communications
Used to heat/cook food
Microwaves in space are used by astronomers to learn about the structure of nearby galaxies, and our own Milky Way
Radar
State one use for infrared radiation
Skin emits infrared light so we can be seen in the dark by someone using night vision goggles
Astronomers use infrared to give information about space. Infrared light maps the dust between stars
Can be used to create thermograms which are used in medicine as a diagnostic tool for cancer, deep vein thrombosis (DVT), circulation problems
Remote controls for TVs, DVD, Bluray players, etc
State one use for ultraviolet radiation
UV lamps in chip shops and butchers to attract insects
Detecting forged bank notes
Hardening some dental fillings
Night club lighting
UV security pens to mark property
State one use for visible light
We use light to see!
Lasers are visible light and are used in Xbox, PlayStation, Bluray players, DVD players
Lasers are also used in laser printers
Aircraft weapon aiming systems
How is the frequency of a wave related to its energy?
The higher the frequency, the more energy the wave has
What is meant by the ‘normal’?
An imaginary line drawn at 90 degrees to the surface. All angles are measured from the normal.
State one use for gamma radiation
Used as a tracer in medicine
Used to treat cancer
Sterilisation of surgical instruments
State one use for X-rays
Create images of bone to detect breaks
Security to scan luggage at airports
What is meant by refraction?
Refraction is the change of speed of a wave as it enters a different medium. Often is is observed as a change in direction of the wave.
Does a light ray always change direction when it is refracted?
No - if the angle of incidence is 0 degrees
What happens to the speed of light as it travels from air into glass?
It slows down
What do waves transfer?
Energy
What is meant by diffraction?
It is the bending of waves round an object
Will long or short wavelengths diffract more?
Long wavelengths diffract more
In the hills why can you pick up a radio signal but not a television signal?
Radio waves are longer wavelengths than television waves.
Radio waves diffract more and can reach the receiver.
What is the difference in the diffraction pattern produced by waves passing through a wide and a narrow gap? (Wavelength is the same)
The narrower the gap, the more diffraction occurs.
What is the difference in the diffraction pattern in a long wavelength and short wavelength passing an object?
The longer wavelength diffracts more
What effect is shown here?
(waves bend over a hill)
Diffraction
What happens to a light ray as it travels from air into glass?
It will slow down and change direction towards the normal
Which colour of light is refracted the least in a triangular prism when white light is shone through it?
Red light
What happens when white light is shone through a triangular prism
The light is refracted and produces a spectrum
Why does a triangular prism produce a spectrum from white light?
Different frequencies/colours of light are refracted by different amounts
Which colour of light is refracted the most in a triangular prism when white light is shone through it?
Blue light
What is the difference between real and apparent depth? Explain how this happens.
We think that the water is shallower than it actually is (apparent depth)
This is because
The light is refracted at the water/air boundary and changes direction away from the normal
Our eyes/brain assume that light travels in straight lines
What is the shape of a concave lens?
A concave lens is thinner in the center and thicker at the edges, resembling a “caved-in” shape.
What happens to a light ray as it travels from water into air?
It speeds up and changes direction away from the normal
What effect does a convex lens have on parallel light rays?
The light rays converge to a focal point by refraction of the light
What is the shape of a convex lens?
A convex lens is thicker in the center and thinner at the edges, resembling an oval or football shape.
What effect does a concave lens have on parallel light rays?
It causes them to diverge due to refraction of the light
What is the difference in the 2 waves shown below?
(one is more spread out and one is closer together)
The bottom wave has a higher frequency / or the top wave has a lower frequency
What is the difference in the 2 waves shown below?
(one it big and high, the other is small and closer to the line)
The top wave has a larger amplitude and so has more energy. (Or the bottom wave has a smaller amplitude so has less energy)
What path will the ray of light take as it passes through the glass block?
(it hits straight into it)
Light ray still experiences a change of speed - it is still refracted but there is no change in direction
What path will the ray of light take as it passes through the glass block?
(it hits on an angle)
The light ray is refracted at the air/glass boundary and glass/air boundary. Both result in a change in direction.
As it enters the block, the speed of the light decreases and it changes direction towards the normal.
As it leaves the block, the speed of the light increases and it changes direction away from the normal.
What are transverse waves
Transverse waves are the “wavey” looking waves and occur when particles vibrate at a right angle to the direction of the wave. Examples include water waves and electromagnetic radiation.
What are longitudinal waves
Longitudinal waves occur when particles vibrate in the same direction of the wave. This can be shown diagrammatically as straight lines and an example of longitudinal waves are sound waves.
What is a period
Time taken for a complete wave to be produced or one whole wave to pass a point.
What is the wave speed
How fast a wave travels from its source in a given amount of time
What is amplitude
Half of the distance from the peak of the wave to the trough.
What is wavelength
The length from one point of one wave to the same point on the next wave. This may be from the start of a wave to the start of the next wave, or from the peak of one wave to the peak of the next wave, trough to trough, etc.
What is frequency
The number of waves produced per second.
The speed of light in a vacuum
The speed of light in a vacuum is 300,000,000m/s (3x10^8m/s) - this is a constant and doesn’t change.
How can you calculate wave speed
Wave speed can be calculated simply using the formula v = d/t.
The speed of all of the waves in the electromagnetic spectrum
3x10^8m/s
Wave equation
Wave speed=frequency x wavelength
What is the angle of incidence
the angle between the beam of light and the normal in the less dense material.
What happens when waves encounter a gap or an object
They bend around it
The speed of sound waves in air
The speed of sound waves in air is 340m/s
What is the angle of refraction
the angle between the beam of light and the normal in the more dense material.
What is the critical angle
the minimum angle at which light is no longer internally refracted. Or, the greatest angle at which light can strike the new medium without being totally reflected.
Is the angle of incidence always bigger than the angle of refraction
yes
