Topic 3.3: Wave Phenomena Questions

State what is meant by the diffraction of a wave.

State what is meant by the superposition of two waves.

Light enters a block of transparent plastic from a vacuum and slows to a speed of 2.0 × 10⁸ m s⁻¹ inside it.

The speed of light in a vacuum is 3.0 × 10⁸ m s⁻¹.

Show that the refractive index of the plastic is 1.5.

Describe the pattern of light seen on a screen when monochromatic, coherent light is passed through two narrow, closely spaced slits.

State what is meant by the refractive index of a transparent material.

The refractive index of ice is 1.31.

Deduce the speed of light inside the ice, taking the speed of light in a vacuum to be 3.0 × 10⁸ m s⁻¹.

State the equation that relates the fringe spacing in a double-slit pattern to the wavelength of the light, the slit separation and the slit-to-screen distance, defining each symbol you use.

A parallel beam of monochromatic light travels through air and strikes the flat surface of a glass block.

The wavefronts make an angle of 58° with the surface in the air.

Inside the glass, the wavefronts make an angle of 33° with the surface.

Which expression gives the refractive index of the glass for this light?

A row of straight waves on the surface of water approaches a harbour wall that has a single narrow opening.

Identify, from the list below, the one change that would make the waves spread out MORE on the far side of the opening: (i) widening the opening; (ii) increasing the wavelength of the waves; (iii) increasing the frequency of the waves.

Two coherent sound sources reach a point with a path difference of 2.5λ.

At that point the sound from one source has amplitude 7.0 units and from the other has amplitude 3.0 units.

Determine the resultant amplitude of the sound at that point.

Two coherent sources send waves to a point P.

The wave from source 1 arrives with amplitude 6.0 mm and the wave from source 2 arrives with amplitude 2.0 mm.

At P the path difference is exactly 4λ.

Calculate the resultant amplitude at P.

Sound travels at about 340 m s⁻¹.

A loudspeaker emits a low note of frequency 85 Hz and a high note of frequency 3400 Hz through the same open doorway, which is about 1 m wide.

Calculate the wavelength of each note, and explain which note can be heard more easily by a listener standing to one side of the doorway (out of the direct line of the speaker).

A particular type of optical-fibre glass has a refractive index of 1.62.

Estimate the critical angle for a boundary between this glass and the surrounding air (refractive index 1.0).

Two small loudspeakers are connected to the same signal generator (so they are coherent) and emit sound of wavelength 0.60 m.

A microphone is placed so that the sound from one speaker travels 1.5 m and from the other travels 2.4 m to reach it.

Determine whether the microphone detects a loud or a quiet sound, showing your reasoning.

The same double-slit apparatus is used first with red light and then with blue light, with the slit separation and the screen distance unchanged.

Explain which colour produces the wider fringe spacing.

Two coherent radio aerials emit waves of wavelength 2.5 m.

At a receiver the wave from the nearer aerial has travelled 30.0 m and the wave from the farther aerial has travelled 40.0 m.

Show that the receiver is at a position of constructive interference.

Two coherent microwave sources point at a detector.

Each source alone would give the detector a wave of amplitude 5.0 units.

At the detector the path difference from the two sources is exactly 3λ.

(a) State whether the interference is constructive or destructive, and

(b) determine the resultant amplitude at the detector. Explain why the sources must be coherent for this result to be observed steadily.

Outline why a wave passing through a gap that is much wider than its wavelength shows only very slight diffraction.

Two slits 0.40 mm apart are lit by light of wavelength 6.4 × 10⁻⁷ m.

Calculate, in radians, the angular separation between two neighbouring bright fringes (maxima) of the pattern.

Two coherent loudspeakers a fixed distance apart emit the same steady note.

A student walks slowly along a line in front of them.

Describe what the student hears and explain, in terms of path difference, why the loudness changes.