P.3.3.2 Refraction, diffraction, and interference

In the diagram, P is the source of a wave of frequency 50 Hz

The wave travels to R by two routes, P → Q → R and P → R. The speed of the wave is 30 m s⁻¹

What is the path difference between the two waves at R in terms of the wavelength λ of the waves?

• 4.8λ

• 8.0λ

• 13.3λ

• 20.0λ

Light from a point source passes through a single slit and is then incident on a double-slit arrangement. An interference pattern is observed on the screen.

What will increase the fringe spacing?

• increasing the separation of the single slit and the double slit

• increasing the width of the single slit

• decreasing the distance between the double slits and the screen

• decreasing the separation of the double slits

When a monochromatic light source is incident on two slits of the same width an interference pattern is produced.

One slit is then covered with opaque black paper.

What is the effect of covering one slit on the resulting interference pattern?

• The intensity of the central maximum will increase

• The width of the central maximum decreases

• Fewer maxima are observed

• The outer maxima become wider

Two loudspeakers emit sound waves.

Which of the following gives the correct frequency condition and the correct phase condition for the waves from the loudspeakers to be coherent?

• Frequency condition: same frequency

  Phase condition: variable phase difference

• Frequency condition: constant frequency difference

  Phase condition: constant phase difference

• Frequency condition: constant frequency difference

  Phase condition: in phase

• Frequency condition: same frequency

  Phase condition: constant phase difference

When a parallel beam of monochromatic light is directed at two narrow slits, S₁ and S₂, interference fringes are observed on a screen.

Which of the following gives the changes that will increase the spacing of the fringes?

• Slit spacing: halved

  Distance from slits to screen: halved

• Slit spacing: halved

  Distance from slits to screen: doubled

• Slit spacing: doubled

  Distance from slits to screen: halved

• Slit spacing: doubled

  Distance from slits to screen: doubled

Two coherent sources generate sound waves of wavelength 0.40 m. The waves leave the sources in phase. A detector some distance from the sources receives the sound waves. The path difference between the detector and the sources is 0.90 m.

What is the phase difference between the waves arriving at the detector?

• zero

• 45°

• 90°

• 180°

Monochromatic light of wavelength 600 nm is used to illuminate a pair of slits 0.50 mm apart. The fringes are observed at a distance of 1.50 m from the slits.

What is the separation of the fringes?

• 2.0 × 10⁻⁷ mm

• 1.8 × 10⁻³ mm

• 5.6 × 10⁻¹ mm

• 1.8 mm

A light source emits light which is a mixture of two wavelength, λ₁ and λ₂. When the light is incident on a diffraction grating it is found that the fifth order of light of wavelength λ₁ occurs at the same angle as the fourth order for light of wavelength λ₂. If λ₁ is 480 nm what is λ₂?

• 400 nm

• 480 nm

• 600 nm

• 750 nm

When comparing X-rays with UV radiation, which statement is correct?

• X-rays have a lower frequency.

• X-rays travel faster in a vacuum.

• X-rays do not show diffraction and interference effects.

• Using the same element, photoelectrons emitted using X-rays have the greater maximum kinetic energy.

Monochromatic light of wavelength 490 nm falls normally on a diffraction grating that has 6 × 10⁵ lines per metre. Which one of the following is correct?

• The first order is observed at angle of diffraction of 17°.

• The second order is observed at angle of diffraction of 34°.

• The third and higher orders are not produced.

• A grating with more lines per metre could produce more orders.