4.4.1: Wave motion Flashcards
Progressive Waves
An oscillation that travels through matter (or sometimes a vacuum) transferring energy from one place to another but not transferring matter. The particles in the matter vibrate as the wave passes through them but do not move along with the wave
Transverse Waves
The oscillations are perpendicular to the direction of wave travel, such as EM waves and waves on the surface of water. The waves have peaks and troughs at the maximum and minimum points of displacement
Longitudinal Waves
The oscillations are parallel to the direction of energy transfer, such as sound waves. Compression - particles are closer together. Rarefaction - particles are more spread out.
Displacement
The distance from the equilibrium position in a particular direction
Amplitude
The maximum displacement from the origin
Wavelength
The minimum distance between two adjacent points on a wave oscillating in phase
Period
The time taken for a full oscillation of one wavelength to pass a given point
Frequency
The number of complete oscillations passing a given point per unit time
Wave speed
The distance travelled by a wave per unit time
Frequency (f)
1/Period (T)
Wavespeed
Frequency (f)/ Wavelength (λ)
Using an oscilloscope to determine the frequency of a wave
The oscilloscope is fed a signal from a microphone. The timebase on the x axis can be set to represent time and the y axis to represent amplitude. The period of the wave can be measured and frequency can be found using 1/T
Phase
The position of an oscillating particle or field at a given time on a wave cycle, expressed in degrees or radians, where 1 full wave cycle = 360 degrees or 2π radians.
Phase difference
The difference in displacement of particles along a wave, or in two different waves, measured in radians.
In Phase
If particles oscillate in step with each other, they are in phase and their phase difference will be 0 or a multiple of 2π.
Out of Phase
The equation x/λ x 2π, where x is the separation in wavelengths between the two particles, can be used to calculate phase difference if the particles oscillate out of phase
Antiphase
When two particles are oscillating with a phase difference of π, π/2 a wavelength out of step with each other, they are in antiphase
Reflection
When a wave changes direction at a boundary between two media, remaining in the original medium, The angle of the incidence is the same as angle of reflection. Wavelength and frequency remain the same
Refraction
When a wave changes direction as it changes speed, when it enters a new medium. Speed changes but frequency stays the same. The wavelength of the wave changes as a result. There will always be some partial reflection at the boundary between the two media.
Diffraction
The spreading out of a wave front as it passes through a gap. The wavelength and frequency remain the same. Maximum diffraction will occur when the gap is the same size as the wavelength.
Polarisation
When the oscillation of a wave is restricted to one plane only.
Using a ripple tank to demonstrate wave properties
A wave is made using an oscillating paddle connected to a motor. The depth of the tank can be adjusted to show refraction. A slit can be added to show diffraction
Using light to demonstrate polarisation
Polarising filters can be used. Two are placed on top of each other. As one of the filters is rotated to 90°, the intensity of light will decrease from 50% to a minimum as light polarised by one filter can’t pass through the second filter
Using microwaves to demonstrate polarisation
A microwave transmitter and receiver are placed on opposite sides of a metal grille. Vertically polarised microwaves are transmitted. With the metal grille oriented vertically, the maximum signal will be received as the microwaves can pass through. As the grille is rotated by 90°, the signal received will fall to a minimum as the vertically polarised microwaves will not pass through the horizontal metal grille.
