Question 1

Which of the following best describes the condition for constructive interference in a double-slit experiment?

Accepted Answer

$$d \sin 	heta = m \lambda$$

Question 2

A soap film (n = 1.33) is illuminated perpendicularly by light of wavelength $$600\ \mathrm{nm} in $$air. What is the minimum nonzero thickness of the film for constructive interference in the reflected light?

Accepted Answer

$$t = \frac{\lambda}{4n}$$

Question 3

In Young's double-slit experiment, the distance between the slits is $$0.2\ \mathrm{mm}$$ and the screen is $$1.0\ \mathrm{m}$$ away. If the wavelength of light used is $$500\ \mathrm{nm}$$, what is the distance between two consecutive bright fringes?

Accepted Answer

$$\Delta y = \frac{\lambda D}{d}$$

Question 4

Which of the following statements about coherence is correct?

Accepted Answer

Coherent sources must have the same frequency and a constant phase relationship.

Question 5

A light wave travels from air ($$n_1 = 1.0$) into glass (n_2$ = 1.5). $$What happens to the wavelength and frequency of the light as it enters the glass?

Accepted Answer

Wavelength decreases, frequency remains the same.

Question 6

In thin film interference, a phase change of $$\pi$$ occurs upon reflection when:

Accepted Answer

Light reflects from a medium of lower refractive index to a higher refractive index.

Question 7

If the path difference between two waves arriving at a point is $$\frac{3\lambda}{2}$$, what type of interference occurs at that point?

Accepted Answer

Destructive interference

Question 8

Which equation gives the intensity at a point on the screen in a double-slit interference pattern, given the amplitudes $$a_1$$ and $$a_2 of $$the two waves and their phase difference $$\delta$$?

Accepted Answer

$$I = a_1$^2 + a_2$^2 + 2a_1a_2 \cos \delta$$

Question 9

A wedge-shaped air film is formed between two glass plates. If the thickness at one end is zero and increases linearly, what pattern is observed under monochromatic light?

Accepted Answer

A series of parallel dark and bright fringes

Question 10

Which of the following will increase the separation between bright fringes in a double-slit experiment?

Accepted Answer

Increasing the wavelength of light

Question 11

A thin film of oil ($$n = 1.4) $$floats on water ($$n = 1.33). $$For constructive interference in the reflected light at normal incidence, the minimum nonzero thickness of the oil film is:

Accepted Answer

$$t = \frac{\lambda}{2n}$$

Question 12

In a double-slit experiment, if the distance between the slits is doubled, what happens to the fringe separation on the screen?

Accepted Answer

It is halved

Question 13

Which of the following is a necessary condition for two sources to produce a sustained interference pattern?

Accepted Answer

They must be coherent

Question 14

A light wave of wavelength $$500\ \mathrm{nm}$$ passes from air into water ($$n = 1.33). $$What is its wavelength in water?

Accepted Answer

$$\lambda_{water} = \frac{\lambda_{air}}{n}$$

Question 15

In thin film interference, which of the following is true for a film with both surfaces in contact with media of higher refractive index?

Accepted Answer

No net phase change occurs upon reflection

Question 16

Which of the following best explains the appearance of colored patterns in a thin oil film on water?

Accepted Answer

Interference of light reflected from the top and bottom surfaces of the film

Wave Optics: Interference and Thin Film Interference

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