Superposition

Learning objectives

Apply the principle of superposition, and explain graphically how two waves travelling in opposite directions form a stationary wave with nodes and antinodes.

Describe stationary-wave experiments with stretched strings, air columns and microwaves, and find the wavelength from the spacing of nodes or antinodes.

Explain diffraction, and describe how the spreading of waves through a gap depends on the gap width compared with the wavelength, as seen in a ripple tank.

Define interference and coherence, describe two-source interference with water waves, sound, light and microwaves, and state the conditions needed to see fringes.

Calculate wavelength, slit separation or fringe spacing for Young's double-slit experiment with λ = ax/D, and predict how the fringe pattern changes.

Apply d sin θ = nλ to a diffraction grating, including finding the highest order visible, and describe measuring the angles of the orders to determine the wavelength of light.