Question 1

Which of the following best describes incoherent light?

Accepted Answer

Light whose waves are not in phase and have random wavefronts.

Question 2

What is the main reason a soap bubble produces a rainbow effect?

Accepted Answer

Constructive and destructive interference of light waves reflecting from different surfaces of the thin film.

Question 3

In Young's double-slit experiment, what causes the bright and dark bands on the screen?

Accepted Answer

Constructive and destructive interference of coherent light waves from the two slits.

Question 4

A double-slit experiment uses monochromatic light. The distance between the slits is $$d$$, the distance to the screen is $$L$$, and the distance from the central bright band to the first-order bright band is $$x. $$What is the wavelength $$\lambda of $$the light?

Accepted Answer

$$\lambda = \frac{x d}{L}$$

Question 5

If the slit separation in a double-slit experiment is increased, what happens to the spacing between the interference fringes on the screen?

Accepted Answer

The spacing decreases.

Question 6

Which condition must be met for constructive interference in thin-film interference when one wave is inverted upon reflection?

Accepted Answer

The extra path length must be an odd number of half wavelengths: $$2d = (m + \frac{1}{2}) \frac{\lambda}{n}$$

Question 7

A soap film (n = 1.33) is illuminated with light of wavelength 521 nm. What is the minimum thickness at which a black stripe appears?

Accepted Answer

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

Question 8

In thin-film interference, what determines whether a reflected wave is inverted?

Accepted Answer

The wave is inverted if it reflects from a medium with a higher index of refraction.

Question 9

A glass lens has a nonreflective coating of magnesium fluoride (n = 1.38). What thickness should the coating be to keep yellow-green light ($$\lambda = 555 nm) $$from being reflected?

Accepted Answer

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

Question 10

Which of the following best explains why the central band in a double-slit interference pattern is white when white light is used?

Accepted Answer

All wavelengths undergo constructive interference at the central band.

Question 11

A student observes colored rings on a puddle and concludes there is an oil slick. If the index of refraction of oil is 1.45 and that of water is 1.33, what is the minimum thickness of oil that could cause a yellow-green ($$\lambda = 555 nm) $$region?

Accepted Answer

$$d = \frac{\lambda}{4 n_{oil}}$$

Question 12

In a double-slit experiment, if the screen is moved farther from the slits, what happens to the distance between the bright bands?

Accepted Answer

The distance increases.

Question 13

Which real-world application uses thin-film interference to reduce glare?

Accepted Answer

Nonreflective coatings on eyeglasses.

Question 14

If both waves are inverted upon reflection in thin-film interference, which thicknesses produce constructive interference?

Accepted Answer

$$d = m \frac{\lambda}{2 n}$$, where $$m = 1, 2, 3, ...$$

Question 15

A laser with $$\lambda = 632.8 nm is $$used in a double-slit experiment. The screen is 1.000 m from the slits, and the first-order bright band is 65.5 mm from the central line. What is the slit separation $$d$$?

Accepted Answer

$$d = \frac{\lambda L}{x}$$

Question 16

Which phenomenon is responsible for the iridescent green color of the tiger beetle's shell?

Accepted Answer

Thin-film interference from multilayer reflectors in the exoskeleton.

Question 17

In a double-slit experiment, what is the equation for the position $$x of $$the $$m-th $$order bright band?

Accepted Answer

$$x = \frac{m \lambda L}{d}$$

Question 18

Which statement about the relationship between wavelength and thin-film interference colors is correct?

Accepted Answer

Different film thicknesses produce constructive interference for different wavelengths, resulting in a rainbow of colors.

Interference of Light: Double-Slit and Thin-Film Phenomena

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