Chapter 4 - Waves Flashcards
What are waves?
Oscillations of particles in a medium that transfer energy.
What are progressive waves?
Waves that move - carrying energy from one place to another
What 3 things can happen to waves?
Reflection, refraction and diffraction
What is reflection?
When wave is bounced back when it hits a boundary e.g. you can see the reflection of light in mirrors.
`What is refraction?
When wave changes direction when it enters a different medium. Change of direction is due to change of speed.
What is diffraction?
When wave spreads out as it passes through a gap or round an obstacle. e.g. you can hear sound from round a corner
What is the amplitude of a wave?
Maximum displacement from the undisturbed position. For transverse wave this is the height of a crest above equilibrium position. Measured in metres.
What is the frequency of a wave?
Number of whole wave cycles (oscillations) per second passing a given point. Measured in Hertz
What is the wavelength of a wave?
Length of one whole wave oscillation or wave cycle. Measured in metres.
What is the phase of a wave?
Measurement of the position of a certain point along a wave cycle.
What is the phase difference?
Amount by which one wave lags behind another wave.
What are phase and phase difference measured in?
Measured in angles (degrees and radians) or fractions of a cycle.
What is the time period of a wave?
Time taken for one whole wave cycle. Measured in seconds
what is the equation linking frequency and time period
frequency = 1/ period
What is the equation for wave speed?
c = frequency x wavelength
Describe experiment to measure speed of sound
- Put two microphones in a straight line a distance ,d, apart. The microphones should have different inputs so the signals from each can be recorded separately.
- Use the signal generator to produce a sound from the loudspeaker and use the computer to record the time between the first and second microphone picking up the sound. (Read off graph of voltage against time)
- Then use speed = distance/ time
What is the speed of electromagnetic waves in a vacuum?
3.0 x 10^8 m/s
What are transverse waves?
Waves where the direction of vibration is perpendicular to the direction of energy propagation.
Give examples of transverse waves?
Electromagnetic waves, ripples of water, S seismic waves
What are longitudinal waves?
- Waves where the direction of vibration of the particles is parallel to the direction of energy propagation.
- Consists of alternate compressions and rarefractions
Give examples of longitudinal waves?
Sound waves and p seismic waves
What is superposition?
When two waves meet, the total displacement at a point is equal to the sum of the individual displacements at that point.
What is a polarised wave?
A wave that oscillates in one direction (plane)
Which types of waves can be polarised?
Transverse waves - provides evidence for the nature of transverse waves.