PHYSICS 202 - Module 32: Interference Diffraction

Monochromatic light of wavelength lambda is equal to 500 nanometers is directed through two narrow parallel slits that are separated by 5 micrometers. There is a viewing screen 1.5 m away from the slits that is used to observe the interference pattern that emerges from the light shining through the slits. The interference pattern is a series of alternating, equally spaced, bright and dark fringes, like that shown in the figure. What is the distance from the central bright fringe to the 3rd order maximum? A. 0.45 m B. 0.53 m C. 0.38 m D. 0.15 m E. 0.075 m

A. 0.45 m

A diffraction grating with 1000 lines per mm is used in a spectrometer to measure the wavelengths of light emitted from a gas discharge tube. What is the wavelength of the first order maximum if the diffraction angle measured is 30°? A. 0.5 micrometers (ym) B. 0.1 micrometers (ym) C. 5 micrometers (ym) D. 1 micrometers (ym)

A. 0.5 micrometers (ym)

You shine monochromatic light of wavelength Y through a narrow slit of width a >> Y and onto a screen that is very far away from the slit. What do you observe on the screen? A. One bright band B. Two bright fringes and three dark fringes C. A series of bright and dark fringes with the central bright fringe being wider and brighter than the other bright fringes D. A series of bright and dark fringes that are of equal widths

A. One bright band

Monochromatic light of wavelength lambda, such as light from a laser, is directed through two narrow parallel slits that are a distance d apart. There is a viewing screen a very long distance R away from the slits that is used to observe the interference pattern that emerges from the light shining through the slits. The interference pattern is a series of alternating, equally spaced, bright and dark fringes, like that shown in the figure. If you replaced the pair of slits of slit spacing d with a new pair of slits that have a spacing d' > d, how is the new interference pattern different from the original one? A. The bright and dark fringes are closer together. B. The bright fringes are brighter. C. The pattern does not change. D. The bright fringes are dimmer. E. The bright and dark fringes are farther apart.

A. The bright and dark fringes are closer together.

Using a green laser with a 500 nm wavelength, you shine light through a narrow slit and onto a screen that is 5 m away from the slit. You then observe a diffraction pattern like that shown in the figure. If you replace the slit with one that is narrower, what happens to the central bright fringe? A. The central bright fringe gets wider. B. The central bright fringe does not change. C. The central bright fringe gets narrower.

A. The central bright fringe gets wider.

Light propagating in a material with index of refraction n1 is incident on a new material with index of refraction n2 < n1. An example of this could be light initially traveling through water and reflecting at a water-air boundary. Some of the incident light reflects at this boundary between materials 1 and 2 and continues to propagate in material 1. How does the phase of the reflected light compare to the phase of the incident light? A. The reflected light is in phase with the incident light. B. The reflected light is one-quarter out of phase with the incident light. C. The reflected light is one-half cycle out of phase with the incident light. D. There is no reflected light because light will not reflect off a material with a lower index of refraction than the initial material.

A. The reflected light is in phase with the incident light.

What does it mean for two light waves to be one-half cycle out of phase? A. When one wave reaches its maximum value the other wave reaches its minimum value. B. One wave has an amplitude equal to half the amplitude of the other wave. C. One wave has a wavelength equal to half the wavelength of the other wave. D.The two waves propagate in directions perpendicular to each other.

A. When one wave reaches its maximum value the other wave reaches its minimum value.

Monochromatic light of wavelength lambda, such as light from a laser, is directed through two narrow parallel slits that are a distance d apart. There is a viewing screen a very long distance R away from the slits that is used to observe the interference pattern that emerges from the light shining through the slits. The distance that light travels from one slit to the screen is r1 and the distance that light travels from the other slit to the screen is r2. The central bright fringe of the interference pattern results due to a path difference, r1 - r2, of zero. What path difference is required to produce the first order DARK FRINGE that is adjacent to the central bright fringe? A. r1-r2=+-1/2Y B. r1-r2=+2Y C. r1-r2=+-Y D. r1-r2=+-3/2Y E. r1-r2=0

A. r1-r2=+-1/2Y

Using a green laser with a 500 nm wavelength, you shine light through a narrow slit and onto a screen that is 5 m away from the slit. You then observe a diffraction pattern like that shown in the figure. If you measure the width of the central bright fringe to be 50 mm, what is the width of the slit? A. 0.2 mm B. 0.1 mm C. 0.05 mm D. 2.0 mm E. 1.0 mm

B. 0.1 mm

If there are 600 lines per mm on a diffraction grating, what is the distance between adjacent slits? A. 1.67 x 10-3 m B. 1.67 x 10-6 m C. 6.00 x 10-3 m D. 6.00 x 10-6 m

B. 1.67 x 10-6 m

You shine monochromatic light of wavelength lambda through a narrow slit of width a = y and onto a screen that is very far away from the slit. What do you observe on the screen? A. One bright band B. A series of bright and dark fringes with the central bright fringe being wider and brighter than the other bright fringes C. A series of bright and dark fringes that are of equal widths D. Two bright fringes and three dark fringes

B. A series of bright and dark fringes with the central bright fringe being wider and brighter than the other bright fringes

A monochromatic light source is directed past a straight edge (like a razor blade) and onto a screen. Why does the shadow produced by the straight edge not have a sharp edge? A. The light waves are composed of many different wavelengths. B. The light waves are made of wavelets that spread out in all directions and interfere with each other. C. The straight edge cannot be held perfectly still. D. The straight edge is not perfectly straight.

B. The light waves are made of wavelets that spread out in all directions and interfere with each other.

You shine monochromatic light of wavelength a >>Y screen that is very far away from the slit. What do you observe on the screen? A. A series of bright and dark fringes with the central bright fringe being wider and brighter than the other bright fringes B. A series of bright and dark fringes that are of equal widths D. Two bright fringes and three dark fringes

C. One bright band

Two light waves of equal wavelength, lambda, are emitted in phase from separate sources and propagate to a common point P. Light wave 1 must travel a longer distance (d1) than light wave 2 (d2) to reach point P, where d1 - d2 is equal to the path difference between the two light waves. If the two waves interfere destructively at point P, what must be true about the path difference between the two light waves? The path difference must be equal to the wavelength. A.The path difference must be equal to zero. B. The path difference must be equal to an integral multiple of the wavelength. C. The path difference must be equal to one-half of the wavelength. D. The path difference must be equal to a half-integral number of wavelengths.

C. The path difference must be equal to one-half of the wavelength.

Light propagating in a material with index of refraction n1 is incident on a new material with index of refraction n2 > n1. An example of this could be light initially traveling through air and reflecting at an air-water boundary. Some of the incident light reflects at this boundary between materials 1 and 2 and continues to propagate in material 1. How does the phase of the reflected light compare to the phase of the incident light? A. There is no reflected light because light will not reflect off a material with a higher index of refraction than the initial material. B. The reflected light is in phase with the incident light. C. The reflected light is one-half cycle out of phase with the incident light. D. The reflected light is one-quarter out of phase with the incident light.

C. The reflected light is one-half cycle out of phase with the incident light.

Monochromatic light of wavelength lambda is equal to 500 nanometers is directed through two narrow parallel slits that are separated by 5 micrometers. There is a viewing screen 1.5 m away from the slits that is used to observe the interference pattern that emerges from the light shining through the slits. The interference pattern is a series of alternating, equally spaced, bright and dark fringes, like that shown in the figure. What is the distance from the central bright fringe to the 3rd order minimum? A. 0.45 m B. 0.53 m C. 0.15 m D. 0.38 m E. 0.075 m

D. 0.38m

A very thin non-reflective coating is applied to glass to reduce the amount of 550-nm wavelength light that is reflected. The refractive index of the coating is 1.3 and the refractive index of the glass is 1.5. What is the thinnest layer of coating that can be used to result in the destructive interference of reflected light with a 550 nm wavelength? A. 550 nm B. 423 nm C. 138 nm D. 106 nm E. 206 nm

D. 106 nm

A thin reflective coating is applied to glass to increase the amount of infrared (IR) light that is reflected from the glass. The refractive index of the coating is 1.7 and the refractive index of the glass is 1.5. What is the thinnest layer of coating that will result in the constructive interference of reflected infrared light with wavelength of 800 nm? A. 235 nm B. 200 nm C. 133 nm D. 118 nm E. 200 nm

D. 118 nm

Using a green laser with a 500 nm wavelength, you shine light through a narrow slit of width 20 micrometers and onto a screen that is 5 m away from the slit. You then observe a diffraction pattern like that shown in the figure. What is the distance from the center of the pattern to the 3rd order dark fringe? A. 1.25 cm B. 3.75 cm C. 12.5 cm D. 37.5 cm

D. 37.5 cm

A diffraction grating with 1000 lines per mm is used in a spectrometer to measure the wavelengths of light emitted from a gas discharge tube. You measure the diffraction angle to be at 20° for one emission line. What would happen to this emission line's diffraction angle if you replaced the diffraction grating with one having 500 lines per mm instead? A. The diffraction angle would be 10°. B. The diffraction angle would greater than 20°. C. The diffraction angle would remain at 20°. D. The diffraction angle would be less than 20°.

D. The diffraction angle would be less than 20°

Two light waves of equal wavelength, lambda, are emitted in phase from separate sources and propagate to a common point P. Light wave 1 must travel a longer distance (d1) than light wave 2 (d2) to reach point P, where d1 - d2 is equal to the path difference between the two light waves. If the two waves interfere CONSTRUCTIVELY at point P, what must be true about the path difference between the two light waves? The path difference must be equal to one-half of the wavelength. A. The path difference must be equal to zero. B. The path difference must be equal to the wavelength. C. The path difference must be equal to a half-integral number of wavelengths. D. The path difference must be equal to an integral multiple of the wavelength.

D. The path difference must be equal to an integral multiple of the wavelength.

What does it mean for two light waves to be in phase? A. The two waves propagate in the same direction. B. The two waves have the same amplitude. C. The two waves have the same wavelength and frequency. D. The two waves reach their maximum value at the same time and their minimum value at the same time.

D. The two waves reach their maximum value at the same time and their minimum value at the same time.

Light of wavelength lambda strikes a plane of glass and some of that light reflects while the rest of the light transmits through the glass. The transmitted beam is then reflected from a glass-water interface, as shown in the figure. The light waves reflected from the air-glass interface and the glass-water interface WILL BE ONE HALF cycle out of phase if the thickness of the glass is _______ . A. y/2(1.33) B. y/2 C. Y/1.33 D. y/2(1.50) E. Y/1.50

D. y/2(1.50)

Light of wavelength lambda strikes a plane of glass and some of that light reflects while the rest of the light transmits through the glass. The transmitted beam is then reflected from a glass-water interface, as shown in the figure. The light waves reflected from the air-glass interface and the glass-water interface WILL BE IN PHASE if the thickness of the glass is _______ A. Y/2(1.33) B. Y/4(1.33) C. Y/4 D. Y/2(1.50) E. Y/4(1.50)

E. Y/4(1.50)

Monochromatic light of wavelength lambda, such as light from a laser, is directed through two narrow parallel slits that are a distance d apart. There is a viewing screen a very long distance R away from the slits that is used to observe the interference pattern that emerges from the light shining through the slits. The distance that light travels from one slit to the screen is r1 and the distance that light travels from the other slit to the screen is r2. The central bright fringe of the interference pattern results due to a path difference, r1 - r2, of zero. What path difference is required to produce the first order BRIGHT FRINGE that is adjacent to the central bright fringe? A. r1-r2= +-3/2Y B. r1-r2=0 C. r1-r2=+-2Y D. r1-r2=+-1/2Y E. r1-r2=+-Y

E. r1-r2=+-Y