Topic 3.3: Wave Phenomena Questions

A swimmer underwater hears a whistle blown at the poolside. The sound crossed from the air into the water.

State and explain how its wavelength changed.

Two loudspeakers driven in phase emit sound of wavelength 0.50 m. Point X is 3.25 m from one speaker and 2.50 m from the other.

Outline why X is a point of destructive interference.

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

A red laser beam shines from the air into a glass prism.

State and explain what happens to the wavelength of the beam inside the prism.

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.

White light falls normally on a diffraction grating.

Outline why the central maximum is white.

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?

State what is meant by the superposition of two waves.

State the condition for the first minimum in single-slit diffraction.

Sound travels at 340 m s⁻¹ in air and 1500 m s⁻¹ in water.

Determine the critical angle for sound going from air into water.

Two loudspeakers connected to the same signal generator give a steady pattern of loud and quiet places. With two separate generators set to the same frequency the pattern does not stay put.

Explain why.

Two loudspeakers in a hall produce quiet spots where almost no sound energy arrives.

Suggest how energy is still conserved.

Monochromatic light falls normally on a diffraction grating.

Outline why there is a bright maximum straight ahead, at the centre of the pattern.

Sound passes from air into a steel rail.

What happens to its frequency, speed and wavelength?

Two coherent slits light a screen.

Outline why the point on the screen directly opposite the midpoint between the slits is bright.

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

Sound travels at 1500 m s⁻¹ in one layer of sea water and 1540 m s⁻¹ in the layer next to it.

Determine the critical angle for sound going from the slower layer into the faster one.

A seismic wave travels at 6.0 km s⁻¹ in one rock layer and 8.0 km s⁻¹ in the next.

Determine the critical angle for the wave going from the slower rock into the faster rock.

Light in air strikes a plastic block at 52° to the normal and refracts to 31°.

Calculate the speed of light in the plastic. (c = 3.0 × 10⁸ m s⁻¹)

Light passes from air into water.

What happens to its frequency, speed and wavelength?