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American System Physics

A Physics Toolkit

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Representing Motion

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Accelerated Motion

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Forces in One Dimension

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Displacement and Force in Two Dimensions

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Motion in Two Dimensions

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Gravitation

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Rotational Motion

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Momentum and Its Conservation

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Energy and Its Conservation

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Thermal Energy

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States of Matter

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Vibrations and Waves

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Sound

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Fundamentals of Light

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Reflection and Refraction

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Interference and Diffraction

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Electrostatics

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Electric Current and Circuits

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Magnetic Fields

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Electromagnetic Induction and Electromagnetism

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Quantum Theory and the Atom

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Solid-State Electronics

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Nuclear and Particle Physics

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Quiz

17.1 Interference of Light – Quiz

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Interference of Light American Physics quiz: free practice for American System Physics. Work through this Interference of Light American Physics quiz and get instant feedback on every answer. If you get stuck, review the 17.1 Interference of Light — Notes lesson. More practice: American System Physics — all units. Syllabus: OpenStax free science textbooks.

  • Questions count: 50
  • Passing grade: A-
  • Time limit:
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1.
The image shows the fringe pattern produced by a double slit with separation 0.35 mm on a screen 2.5 m away. Using the scale, what is the wavelength of the light?
Dr Dabour Hub Academy - figure 1
5.9 × 10⁻⁷ m
5.9 × 10⁻⁶ m
6.7 × 10⁻⁷ m
3.0 × 10⁻³ m
2.
A student varied the screen distance L for a double slit of separation 0.20 mm and plotted fringe spacing x against L (graph shown). The best-fit line has gradient 2.8 mm per metre. What is the wavelength?
Dr Dabour Hub Academy - figure 2
0.014 m
5.6 × 10⁻⁴ m
5.6 × 10⁻⁷ m
7.1 × 10⁻⁵ m
3.
In the x–L experiment shown in the graph, what does a straight line through the origin tell you?
Dr Dabour Hub Academy - figure 3
x is inversely proportional to L
The wavelength increases as the screen is moved back
The slit separation changes with L
x is directly proportional to L, as predicted by x = λL/d
4.
Sources S1 and S2 in the diagram emit in phase with wavelength 0.40 m. What type of interference occurs at P?
Dr Dabour Hub Academy - figure 4
Destructive, because the path difference is 1.5 wavelengths
Constructive, because the path difference is 3 wavelengths
Destructive, because the paths are different lengths
Constructive, because the path difference is ½ wavelength
5.
The diagram shows two in-phase sources emitting water waves of wavelength 2.0 cm. What happens at P?
Dr Dabour Hub Academy - figure 5
Constructive interference: path difference is 3.0 cm = 1½λ
Constructive interference: the paths meet at P
Destructive interference: path difference is 3.0 cm = 1½λ
Destructive interference: path difference is 2.0 cm = λ
6.
The graph shows waves A and B arriving at the same point. What is their phase difference and the resultant amplitude?
Dr Dabour Hub Academy - figure 6
0°; resultant amplitude 2.5 cm
180°; resultant amplitude 0.5 cm
180°; resultant amplitude 2.5 cm
90°; resultant amplitude 0 cm
7.
Waves A and B in the graph meet at a point. What is the amplitude of the resultant wave?
Dr Dabour Hub Academy - figure 7
0 cm
1.0 cm
2.0 cm
1.4 cm
8.
The diagram shows a thin oil film (n = 1.40) with air above and below. Using 2t = (m + ½)λ/n with m = 0, which wavelength is most strongly reflected?
Dr Dabour Hub Academy - figure 8
4.8 × 10⁻⁷ m
3.4 × 10⁻⁷ m
6.7 × 10⁻⁷ m
6.7 × 10⁻⁶ m
9.
In the thin-film diagram, which two waves interfere to produce the colours seen?
Dr Dabour Hub Academy - figure 9
The incident ray and ray 1
Two rays transmitted into the air below
Ray 2 and light from a second lamp
Ray 1 reflected from the top surface and ray 2 reflected from the bottom surface
10.
The table shows results from a double-slit experiment. Which variable is the independent variable?
The slit-to-screen distance L
The fringe spacing x
The wavelength of the laser
The slit separation d
11.
For the experiment in the table, which pair of quantities must be kept constant for a fair test?
The fringe spacing and the screen distance
The laser (wavelength) and the double-slit slide (d)
The room temperature and the screen colour only
The number of fringes and the screen distance
12.
Four lasers are tested with the same double slit (d = 0.25 mm) and screen distance (2.0 m). Using the table, which laser emits red light (λ close to 650 nm)?
Laser A
Laser C
Laser B
Laser D
13.
Using the same table of four lasers, which laser has a wavelength outside the visible range of about 400–700 nm?
Laser A
Laser B
Laser C
Laser D
14.
A laser shines on two slits 0.25 mm apart. On a screen 3.0 m away the fringe spacing is 7.2 mm. What is the wavelength of the light?
6.0 × 10⁻⁷ m
86 m
5.4 × 10⁻⁶ m
6.0 × 10⁻⁴ m
15.
Blue light of wavelength 450 nm passes through two slits 0.15 mm apart. What fringe spacing is seen on a screen 2.0 m away?
3.4 × 10⁻¹¹ m
6.0 × 10⁻³ m
6.0 × 10⁻⁶ m
6.0 m
16.
Green light of wavelength 520 nm gives fringes 3.9 mm apart on a screen 1.5 m from a double slit. What is the slit separation?
1.1 × 10⁻³ m
0.20 m
2.0 × 10⁻⁴ m
1.4 × 10⁻⁹ m
17.
Red light (650 nm) passes through slits 0.30 mm apart. How far from the slits must the screen be placed for a fringe spacing of 5.0 mm?
0.23 m
23 m
11 m
2.3 m
18.
A student measures one fringe spacing directly with a ruler marked in mm and gets 4 mm. A second student measures across 10 spacings and gets 42 mm. Why is the second method better?
It removes all systematic error from the slit separation
The ±1 mm reading uncertainty is shared over 10 spacings, so the percentage uncertainty in x is about ten times smaller
It makes the fringes brighter and so easier to see
It changes the wavelength of the light to a value that is easier to measure
19.
Two coherent loudspeakers in phase emit sound of wavelength 0.50 m. At point P the path difference is 1.25 m. What is heard at P?
A quiet spot, because 1.25 m is 2½ wavelengths
A loud spot, because 1.25 m is a whole number of wavelengths
A loud spot, because the path difference is greater than λ
A quiet spot, because 1.25 m is 2 wavelengths
20.
Two light waves meet on a screen. Which link between how they arrive and what is observed is right?
Antiphase (180°) — dark fringe for light, quiet spot for sound
In phase (0°) — dark fringe for light
Antiphase (180°) — loud spot for sound
In phase (360°) — zero resultant amplitude
21.
White light is used in a double-slit experiment. What is seen next to the central fringe?
Coloured fringes with red nearer the centre
Only white fringes, all equally spaced
A single dark band with no colour
Coloured fringes with blue edges nearer the centre and red further out
22.
A soap film (n = 1.33) in air reflects light strongly when 2t = (m + ½)λ/n. What is the smallest film thickness that strongly reflects light of wavelength 550 nm?
1.4 × 10⁻⁷ m
1.0 × 10⁻⁷ m
2.1 × 10⁻⁷ m
1.8 × 10⁻⁷ m
23.
Why does an anti-reflection coating on a lens have a thickness of about a quarter of a wavelength (in the coating)?
The wave reflected from the lower surface travels an extra half wavelength, so the two reflected waves cancel
It makes the lens absorb all the light
A quarter wavelength makes the coating refract more strongly
It doubles the amplitude of the reflected light
24.
The colours of a vertical soap film change as it drains and gets thinner. Which explanation is best?
The soap absorbs different colours as it dries
Gravity changes the frequency of the light
The thickness changes the extra path 2t, so different wavelengths meet the constructive condition
The film acts as a prism and refracts white light
25.
Which statement best explains why a laser is ideal for Young's double-slit experiment?
It is the only light that diffracts
It has a very long wavelength
It travels faster than ordinary light
It is monochromatic and coherent, giving bright, sharp, stable fringes
26.
Which safety precaution is essential when doing the double-slit experiment with a laser?
Never look directly into the beam or its reflections
Wear gloves in case the slits get hot
Keep the room brightly lit at all times
Use a mercury thermometer near the screen
27.
A student's fringes are too close together to measure accurately. Which change would best increase the fringe spacing?
Use slits that are further apart
Move the screen further from the slits
Use a blue laser instead of red
Make the room darker
28.
You are to measure the wavelength of a laser with a double slit of unknown separation. Which extra step allows d to be found?
Measure the brightness of the central fringe
Measure the width of the laser box
First use a laser of known wavelength with the same slits, measure x and L, and calculate d = λL/x
Count how many fringes appear on the screen
29.
A student measures L from the laser box to the screen instead of from the slits. What type of error does this cause?
A random error that averages out with repeats
No error, because L does not appear in the equation
A systematic error making λ too large
A systematic error: every L is too large, so every calculated λ is too small
30.
A glossary card matches each interference word to a definition. Which card is accurate?
Fringe spacing — distance between centres of adjacent bright fringes
Path difference — the phase angle between two waves
Coherent sources — sources with the same amplitude
Monochromatic light — light containing all colours
31.
For the third dark fringe from the centre in a double-slit pattern (m = 2), the path difference is _____ wavelengths.
2
3
1½
2½
32.
At the central bright fringe of a double-slit pattern the path difference is _____.
zero
½λ
λ
d
33.
With white light, the central fringe of a double-slit pattern is _____ because every wavelength has zero path difference there.
white
red
violet
dark
34.
The table shows that doubling the slit separation (trials 1 and 2) halves the fringe spacing. True or false?
False, because x doubles when d doubles
True
False, because x stays the same
True only because L was also changed
35.
Comparing trials 1 and 3 in the table is a fair test of how L affects x. True or false?
False, because d changed between them
False, because the wavelength changed
True
True only if the slits were changed too
36.
According to the path-difference data, a listener standing at Q hears loud sound. True or false?
True, because 0.60 m is a whole number of wavelengths
True, because every point with a path difference is loud
False, because Q is loud only if the path difference is zero
False, because 0.60 m is 1½ wavelengths, so Q is quiet
37.
In the table, point P is a loud spot. True or false?
True
False, because 0.80 m is 2½ wavelengths
False, because P is too far from the speakers
True only if the speakers are out of phase
38.
The table suggests thin-film colours appear only when the film thickness is comparable with the wavelength of light. True or false?
False, because the thick window shows the strongest colours
True
False, because thickness has no effect on the colours
True only for glass
39.
A phase difference of 360° between two waves of the same frequency produces the same interference result as a phase difference of 0°. True or false?
False, because 360° always gives cancellation
True only for sound waves
False, because 360° is half a cycle
True
40.
After two water pulses pass through each other, each pulse continues with its original shape and speed. True or false?
False, because the pulses permanently merge
True
False, because the smaller pulse is absorbed
True only if the pulses have equal amplitude
41.
Two identical car headlamps shining on a wall produce a stable pattern of bright and dark fringes. True or false?
True, because they have the same colour
True only at night
False, because separate lamps are not coherent
False, because light cannot interfere
42.
Coherent sources must emit waves with the same frequency and a constant phase difference. True or false?
False, because coherent means equal amplitude
False, because they need opposite phase
True only for lasers
True
43.
At a dark fringe, light energy is destroyed by destructive interference. True or false?
False, because energy is redistributed to the bright fringes
True, because the amplitude is zero there
True only for monochromatic light
False, because dark fringes still receive full intensity
44.
Young passed light from a single source through two slits so that both slits were fed by the same wavefront. True or false?
False, because Young used two separate lamps
True
False, because Young used a laser
True only because he used white light
45.
Interference of sound and of water waves shows interference is a general property of waves. True or false?
False, because only light can interfere
True only for transverse waves
True
False, because sound cannot superpose
46.
If the slit separation in Young's experiment is halved while L and λ stay the same, the fringe spacing halves. True or false?
True, because x is proportional to d
True only if the screen is moved closer
False, because x does not depend on d
False, because x = λL/d so the fringe spacing doubles
47.
Replacing a green laser with a red laser in a double-slit experiment makes the fringes further apart. True or false?
True
False, because red light has a shorter wavelength
False, because the colour has no effect
True only if d is also doubled
48.
The equation λ = xd/L is valid only when L is much larger than d. True or false?
False, because it is exact for all distances
True
False, because it requires d to be larger than L
True only for sound waves
49.
Monochromatic light gives sharper, evenly spaced fringes than white light in a double-slit experiment. True or false?
False, because white light gives sharper fringes
False, because monochromatic light gives no fringes
True
True only for blue light
50.
A phase change of half a cycle can occur when light reflects from a material of higher refractive index. True or false?
False, because reflection never changes phase
True
True only for reflection from a lower-index material
False, because only sound changes phase
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