Unit 7 Waves

Physics

Define wavelength

The distance between adjacent peaks/ troughs

Describe how you could test whether the microwaves leaving the transmitter are plane polarised. (3)

• Place a polaroid between the transmitter and the reflector

• rotate it 90 degrees

• this causes no signal

State three conditions that must be satisfied in order that two waves may interfere. (3)

• same type of waves (both transverse/ longitudinal)

• same direction of polarisation

• meet at a point

state the principle of superposition (3)

• when two or more waves meet

• the resultant displacement

• is the sum of the individual displacements

Define diffraction

• When a wave is incident on an edge or a slit

• The wave spreads out

State a condition for using d sin θ = n λ

no path difference of light before entering grating

Explain by reference to the properties of stationary waves, why the heaps of dust are formed (3)

• at antinodes there are no heaps as the wave has maximum amplitude of vibration

• at nodes there are heaps as the amplitude of vibration is zero

• dust is pushed to the nodes

Explain by reference to the formation of a stationary wave, what is meant by the speed of a wave in a tube (3)

• stationary waves are formed by the superposition of the wave travelling down the tube and the reflected wave

• the speed refers to the speed of the incident wave