22: PhET Tutorial: Wave Interference

Part A:
How does the amplitude of the wave depend on the distance from the source?

A) The amplitude decreases with distance.
B) The amplitude increases with distance.
C) The amplitude is constant.

SOLUTION:
Comparing the reading from the detector placed close to the source with a reading placed farther away from the source, one can see that the amplitude decreases as distance increases. Option A)

Part B:
Which statement best describes how the intensity of the wave depends on position along the screen?

A) The intensity is roughly constant.
B) The intensity is large near the middle of the screen, then decreases to nearly zero, and then increases again as the distance from the middle of the screen increases.
C) The intensity is a maximum near the middle of the screen (directly to the right of the source) and significantly decreases above and below the middle of the screen.

SOLUTION:
The intensity graph appears to be a vertical line, or pretty much constant all along the screen. So it can be assumed that the intensity is roughly constant, or option A)

Part C:
Which statement best describes how the intensity of the wave depends on position along the screen?

A) The intensity is large near the middle of the screen, then decreases to nearly zero, and then increases again as the distance from the middle of the screen increases.
B) The intensity is roughly constant.
C) The intensity is a maximum near the middle of the screen (directly to the right of the source) and significantly decreases above and below the middle of the screen.

SOLUTION:
Just as in the previous question, the intensity graph appears to be a vertical line, or roughly constant. Option A)

Part D:
Which statement best describes how the intensity of light on the screen behaves?

A) The intensity is large near the middle of the screen, then decreases to nearly zero, and then increases again as the distance from the middle of the screen increases.
B) The intensity is roughly constant.
C) The intensity is a maximum near the middle of the screen (directly to the right of the source) and significantly decreases above and below the middle of the screen.

SOLUTION:
The intensity graph appears to be large in the middle of the screen, drop down to zero and then increase again as distance from the middle increases. This is option A)

Part E:
How do the distances r1 and r2 compare?

A) The difference in the distances is equal to half the wavelength of the wave.
B) The difference in the distances is equal to the wavelength of the wave.
C) The difference in the distances is equal to a quarter of the wavelength of the wave.
D) The distances are the same.

SOLUTION:
my measured wavelength of green light ~ 600 nm
r1 = 2790.33 nm
r2 = 3364.33 nm
r2-r1 = 574 nm
this shows that the difference in the distances is roughly equal to the wavelength of the wave, or option B)

Part F:
Compare the distances from the first location nearest the middle of the screen where the intensity is nearly zero (dark fringe) to each of the two slits. How do the distances compare?

A) The difference in the distances is equal to a quarter of the wavelength of the wave.
B) The distances are the same.
C) The difference in the distances is equal to half the wavelength of the wave.
D) The difference in the distances is equal to the wavelength of the wave.

SOLUTION:
r1 = 2807.86 nm
r2 = 3160.03 nm
r2 - r1 = 352.17 nm
the difference in distances is roughly equal to half the measured wavelength, or option C)

Part G:
How does the distance between consecutive bright fringes depend on the wavelength of the light?

A) The spacing of the fringes does not change when the wavelength changes.
B) The fringes get closer together as the wavelength increases.
C) The fringes get farther apart as wavelength increases.

SOLUTION:
distance btwn bright fringes w/ green wavelength- 418.04 nm
distance btwn bright fringes w/ blue wavelength- 243.72 nm

since blue has a shorter wavelength than green and blue's distance btwn is less than greens, it can be said that either 
distance between bright fringes decreases as wavelength is decreased
or distance between bright fringes increases as wavelength is increased
the second one satisfies option C)

Part H:
How does the distance between consecutive bright fringes depend on the slit separation?

A) The fringes get farther apart as the slit separation increases.
B) The fringes get closer together as the slit separation increases.
C) The spacing of the fringes does not change when the slit separation changes (just the brightness changes).

SOLUTION:
(I used yellow light)
distance btwn bright fringes w/ 875 slit separation- 556.94 nm
distance btwn bright fringes w/ 1750 slit separation- 290.11 nm
so the lesser separation resulted in a greater distance, therefore it can be said either
the distance between the bright fringes increases as slit separation decreases 
or the distance between the bring fringes decreases as slit separation increases
the second satisfies option B)

PART I:
How does the distance between the bright fringes depend on the slit width (for slit widths less than the wavelength of the light)?

A) The spacing of the fringes does not change when the slit width changes.
B) The fringes get closer together as the slit width increases.
C) The fringes get farther apart as the slit width increases.

SOLUTION:
for ~ 700 nm wavelength
distance btwn bright fringes w/ notch 1 slit width(~197.32 nm)- 197.32 nm
distance btwn bright fringes w/ notch 2 slit width(~498.93 nm)- 200.31 nm
so it can be said that the spacing of the fringes does not change as the slit width changes for slit widths less than the wavelength of the light, or option A)

Part J:
How does the distance between the bright fringes depend on the amplitude of the wave?

A) The fringes get farther apart as the amplitude increases.
B) The spacing of the fringes does not change when the amplitude changes (just the brightness changes).
C) The fringes get closer together as the amplitude increases.

SOLUTION:
Option B)

Part K:
Does interference occur when water or sound waves encounter a barrier with two slits?

A) Interference also occurs for sound waves, but not for water waves.
B) Interference also occurs for water waves, but not for sound waves.
C) Yes, interference also occurs for both of these types of waves.
D) No, it only occurs for light.

SOLUTION:
Interference is a very common phenomenon that can occur with any type of wave.
Option C)