Topic 4.4 Wave Behavior

Which diagram shows the shape of the wavefront as a result of the diffraction of plane waves by an object?

• A

• B

• C

• D

Light is incident at the boundary between air and diamond. The speed of light in diamond is less than the speed of light in air. The angle of incidence i of the light is greater than the critical angle. Which diagram is correct for this situation?

• A

• B

• C

• D

Monochromatic light is used to produce double-slit interference fringes on a screen. The fringe separation on the screen is y. The distance from the slits to the screen and the separation of the slits are both doubled, and the light source is unchanged. What is the new fringe separation on the screen?

• y4\frac{y}{4}

  4

  
  

  y

  ​

• yy

  y

• 2y2y

  2y

• 4y4y

  4y

Three quantities used to describe a light wave are

I.   frequency

II.  wavelength

III. speed.

Which quantities increase when the light wave passes from water to air?

• I and II only

• I and III only

• II and III only

• I, II and III

A glass block has a refractive index in air of n_g. The glass block is placed in two different liquids: liquid X with a refractive index of n_X and liquid Y with a refractive index of n_Y.

In liquid X n_g/n_X=2   and in liquid Y n_g/n_Y=1.5. What is [speed of light in liquid X / speed of light in liquid Y] ?

A beam of coherent monochromatic light from a distant galaxy is used in an optics experiment on Earth.

The beam is incident normally on a double slit. The distance between the slits is 0.300 mm. A screen is at a distance D from the slits. The diffraction angle θ is labelled.

A series of dark and bright fringes appears on the screen.

Explain how a dark fringe is formed. [3 marks]

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Answer explanation

superposition of light from each slit / interference of light from both slits

with path/phase difference of any half-odd multiple of wavelength/any odd multiple of π (in words or symbols)

producing destructive interference

[3 marks]

A beam of coherent monochromatic light from a distant galaxy is used in an optics experiment on Earth.

The beam is incident normally on a double slit. The distance between the slits is 0.300 mm. A screen is at a distance D from the slits. The diffraction angle θ is labelled.

The wavelength of the beam as observed on Earth is 633.0 nm. The separation between a dark and a bright fringe on the screen is 4.50 mm.

Calculate D. [2 marks]

Answer explanation

evidence of solving for

D «D = sd/λ»

«4.50×10⁻³×0.300×10⁻³/633.0×10⁻⁹ × 2» = 4.27 «m»

[2 marks]

A beam of coherent monochromatic light from a distant galaxy is used in an optics experiment on Earth.

The beam is incident normally on a double slit. The distance between the slits is 0.300 mm. A screen is at a distance D from the slits. The diffraction angle θ is labelled.

The air between the slits and the screen is replaced with water. The refractive index of water is 1.33.

Calculate the wavelength of the light in water. [1 mark]

Answer explanation

633.0/1.33 = 476 «nm»

[1 mark]

A beam of coherent monochromatic light from a distant galaxy is used in an optics experiment on Earth.

The beam is incident normally on a double slit. The distance between the slits is 0.300 mm. A screen is at a distance D from the slits. The diffraction angle θ is labelled.

The air between the slits and the screen is replaced with water. The refractive index of water is 1.33.

State two ways in which the intensity pattern on the screen changes. [2 marks]

Answer explanation

distance between peaks decreases

intensity decreases

[2 marks]