Define longitudinal wave
A wave with a direction of vibration that is parallel to the direction of energy transfer
Define transverse wave
A wave with a direction of vibration that is perpendicular to the direction of energy transfer.
Define amplitude of a wave
The maximum displacement of the wave from the equilibrium position
Give three examples of waves that are transverse
- Electromagnetic radiation e.g misrowaves, infrared etc
- Surface of water
- s waves
Give three examples of longitudinal waves
State the order of the electromagnetic spectrum from lowest frequency/energy to highest frequency/energy
X - rays
How do we know waves transfer energy?
- Electromagnetic waves heats things up when they are absorbed
- X-rays and gamma rays knock electrons out of their orbits (ionisation)
- Loud sounds cause oscillations of air particles which make things vibrate.
- Waves power can be used to generate electricity.
The distance from a point on the wave to the same point on the adjacent wave. It is measured in meters
Is the number of waves that pass a point every second. It is measured in hertz (Hz)
It is the time taken for each one whole wave to pass a fixed point. It is measured in seconds (s)
Define phase difference
the amount by which one wave lags behind another wave.
What units can phase difference be measured in?
Phase and phase difference can be measured in:
- fractions of a cycle.
Waves with the same frequency, a constant phase difference and a similar amplitude
Describe an experiment to measure the speed of sound
- Start with signal generator + 2 microphones in phase.
- Move 1 microphone and measure the distance between them.
- Measure the time delay using the picoscope
- collect a range of distance and time measurements.
- Draw a graph of distance against time.
- Use the gradient to find the speed of sound.
Restriction of a wave to a single plane
If there are two polarising filters inbetween an observer and light, if one is turned about 360 degrees, what would the observer see?
Variation in intensity between max and min Two maxima and two minimum in 360 degree rotation
What waves can be polarised?
State one application of a polarising filter and a reason for its use
Camera/sunglasses - Reduce glare
LCD screens - less power is required
3D glasses - Enhanced viewing experience
Looking at stress/strain/fractures of materials
Light was originally thought to be a longitudinal wave, why do we now know it is transverse?
It was discovered light was polsriased by reflection so must be transverse.
Explain why it is important to correctly align the aerial of a TV to receive the strongest signal
Transmitted radio waves are often polarised.
Aerial rods must be aligned in the same plane of the wave
Interference – When two waves arrive at the same point and at the same time, the resultant displacement is given by the algebraic sum of the two individual displacements.
Define constructive interference
If two waves meet exactly in phase the amplitudes add up to produce large crests and troughs
Define destructive interference
If two waves meet exactly out of phase the amplitudes cancel to produce no crests and troughs
State the difference between a progressive wave and a standing wave.
Progressive (travelling wave) – transfer energy from one region to another e.g light and sound
Standing (stationary waves) – Are fixed in space and do not travel. They are caused by the superposition of two identical waves. e.g waves on a guitar string
How are stationary waves formed?
- Vibrations cause waves travels along the string towards the pulley.
- The waves reflect from the pulley and travel back to the vibration generator.
- The two waves meet and constructively and destructively interfere.
What are the conditions required for standing waves to be formed?
The waves must have the same frequency and amplitude.
Define a node
NO DisplacEment – Positive displacement from one wave is cancelled by an equal negative displacement from the other wave. (Destructive interference)
Define an antinode
A point of maximum displacement (constructive interference)
For a string that is fixed at both ends what are the rules for nodes and antinodes?
There must be a node at each end.