3.3.1 Progressive and Stationary Waves

Definitions

Define a progressive wave

A wave that transfers energy from one point to another without transferring matter

Explain how polarisation acts as evidence for the nature of transverse waves

Polarisation restricts oscillations to a single plane containing the direction of energy transfer. This is only possible if the oscillations are perpendicular to the direction of wave travel. Longitudinal waves oscillate parallel, so they cannot be polarised.

State an application of polarisation

TV aerial alignment: TV signals are polarised by the orientation of the transmitter rods. The receiving aerial rods must be aligned in the same plane of polarisation to get maximum signal.

Define phase difference and state its units

The fraction of a cycle between two vibrating particles or waves. Measured in degrees or radians.

Define displacement and amplitude of a wave

Displacement is the distance and direction of a vibrating particle from its equilibrium position. Amplitude is the maximum displacement of a vibrating particle from its equilibrium position.

Define wavelength, period and frequency

Wavelength is the least distance between two adjacent particles oscillating in phase. Period is the time taken for one complete wave cycle to pass a given point. Frequency is the number of whole wave cycles passing a fixed point per second.

Describe what a longitudinal wave is and give two examples

A wave where particle oscillations are parallel to the direction of energy transfer. It consists of compressions (high pressure) and rarefactions )low pressure. For example, sound waves and seismic p-waves.

Describe what a transverse wave is and give two examples

A wave where all the particle oscillations are perpendicular to the direction of energy transfer. For example, all electromagnetic waves and seismic s-waves.

Explain how a stationary wave is formed on a string

A progressive wave travels down the string and reflects at the fixed end. The reflected wave travels in the opposite direction with the same frequency, wavelength, and amplitude. The two waves superpose (interfere).

Contrast how energy behaves in a stationary wave versus a progressive wave

In a progressive wave energy is transferred through the medium in the direction of propagation. In a stationary wave, energy is trapped/stored within the nodes and antinodes so no net transfer of energy occurs.

Define node and antinode

A node is a point of zero amplitude where the two superposing waves meet completely out of phase and undergo destructive interference. An antinode is a point of maximum amplitude where the waves meet in phase and undergo constructive interference.