Question 1

A laser beam passes through a 0.1-mm-wide slit in an opaque screen, as shown in the diagram. What phenomenon is primarily responsible for the spreading of light behind the slit?

Accepted Answer

Diffraction

Question 2

In a double-slit experiment, the distance between the slits is $$d$$, the wavelength of the light is $$\lambda$$, and the screen is a distance $$L$$ away. The position $$y_m of $$the $$m-th $$bright fringe is given by which equation?

Accepted Answer

$$y_m = m \dfrac{\lambda L}{d}$$

Question 3

Constructive interference in a double-slit experiment occurs when the path difference between the two slits is:

Accepted Answer

$$\Delta r = m\lambda$$

Question 4

A helium-neon laser ($$\lambda = 633\ \mathrm{nm}) $$illuminates two slits spaced $$0.40\ \mathrm{mm}$$ apart. A bright fringe is observed $$9.5\ \mathrm{mm}$$ from the center on a screen $$2.0\ \mathrm{m}$$ away. What is the fringe number $$m$$?

Accepted Answer

$$m = 6$$

Question 5

In a double-slit experiment, the intensity of the bright fringes decreases as you move away from the central maximum. What is the main reason for this decrease?

Accepted Answer

The light intensity from each slit by itself is not uniform.

Question 6

A double-slit interference pattern is observed on a screen $$1.0\ \mathrm{m}$$ behind two slits spaced $$0.30\ \mathrm{mm}$$ apart. The distance from the center of one bright fringe to the ninth bright fringe is $$1.6\ \mathrm{cm}. $$What is the wavelength of the light?

Accepted Answer

$$\lambda = 533\ \mathrm{nm}$$

Question 7

If the barbs on a feather are spaced at $$50$$ per mm, what is the first-order diffraction angle for blue light of $$450\ \mathrm{nm}$$?

Accepted Answer

$$	heta = 1.29^\circ$$

Question 8

A sodium lamp passes through a diffraction grating with $$1000$$ slits per millimeter. Two bright yellow fringes are observed at $$72.88\ \mathrm{cm}$$ and $$73.00\ \mathrm{cm}$$ from the central maximum on a screen $$1.000\ \mathrm{m}$$ behind the grating. What is the approximate wavelength difference between these two fringes?

Accepted Answer

$$\Delta \lambda \approx 1.2\ \mathrm{nm}$$

Question 9

A researcher observes diffraction maxima at $$13^\circ$$ and $$25^\circ$$ for yellow light ($$\lambda = 570\ \mathrm{nm}) $$from a beetle's ridges. What is the spacing $$d of $$the ridges?

Accepted Answer

$$d = 2.60\ \mu\mathrm{m}$$

Question 10

A thin film of material with $$n = 1.38 is $$coated onto a plastic lens ($$n = 1.55). $$What is the thinnest film that will minimize reflection for $$\lambda = 550\ \mathrm{nm}$$?

Accepted Answer

$$t = 100\ \mathrm{nm}$$

Question 11

The peacock fern has membranes with thickness $$70\ \mathrm{nm}$$ and index of refraction $$n = 1.45. $$What is the longest wavelength of visible light for which there is constructive interference?

Accepted Answer

$$\lambda = 203\ \mathrm{nm}$$

Question 12

Light from a helium-neon laser ($$\lambda = 633\ \mathrm{nm}) $$passes through a narrow slit and is seen on a screen $$2.0\ \mathrm{m}$$ behind the slit. The first minimum in the diffraction pattern is $$1.2\ \mathrm{cm}$$ from the middle of the central maximum. How wide is the slit?

Accepted Answer

$$a = 0.106\ \mathrm{mm}$$

Question 13

Light from a helium-neon laser ($$\lambda = 633\ \mathrm{nm}) $$passes through a $$0.50\ \mathrm{mm}-$$diameter hole. How far away should a viewing screen be placed to observe a diffraction pattern whose central maximum is $$3.0\ \mathrm{mm} in $$diameter?

Accepted Answer

$$L = 2.4\ \mathrm{m}$$

Question 14

Which of the following best describes the Huygens-Fresnel principle as illustrated in the diagrams?

Accepted Answer

Each point on a wavefront acts as a source of new spherical wavelets.

Question 15

In single-slit diffraction, the condition for the first minimum is given by:

Accepted Answer

$$a \sin 	heta = \lambda$$

Question 16

A diffraction grating with $$N$$ slits per unit length produces maxima at angles $$	heta$$ given by which equation?

Accepted Answer

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

Double-Slit Interference and Diffraction: Step-by-Step Physics Guidance

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