Wave Optics
Q. In a thin film of oil on water, which color is most likely to be seen at normal incidence?
A.
Red
B.
Blue
C.
Green
D.
Yellow
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Solution
The color seen depends on the thickness of the film and the wavelength of light. Typically, red is seen due to constructive interference for certain thicknesses.
Correct Answer: A — Red
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Q. In a thin film of oil on water, which color will appear at the center of the film if the oil has a thickness of λ/2?
A.
Red
B.
Blue
C.
Green
D.
No color
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Solution
At the center of the film with thickness λ/2, destructive interference occurs for all wavelengths, leading to no color.
Correct Answer: D — No color
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Q. In a thin film of oil on water, which color will be most prominently visible due to constructive interference?
A.
Red
B.
Blue
C.
Green
D.
Yellow
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Solution
The color that is most prominently visible depends on the thickness of the film and the wavelength of light. Typically, shorter wavelengths like blue are enhanced due to constructive interference.
Correct Answer: B — Blue
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Q. What happens to the diffraction pattern when the slit width is decreased?
A.
Pattern becomes wider
B.
Pattern becomes narrower
C.
No change in pattern
D.
Pattern disappears
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Solution
Decreasing the slit width increases the diffraction angle, causing the diffraction pattern to become wider.
Correct Answer: A — Pattern becomes wider
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Q. What happens to the fringe pattern in Young's double-slit experiment if the distance to the screen is halved?
A.
Fringe width increases
B.
Fringe width decreases
C.
Fringe separation remains the same
D.
Fringe visibility decreases
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Solution
Fringe width (β) is inversely proportional to the distance to the screen (D). If D is halved, the fringe width decreases.
Correct Answer: B — Fringe width decreases
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Q. What is the effect of increasing the slit width in a double-slit experiment on the interference pattern?
A.
Fringe width increases
B.
Fringe width decreases
C.
Fringe visibility increases
D.
Fringe visibility decreases
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Solution
Increasing the slit width reduces the coherence of the light waves, leading to decreased fringe visibility.
Correct Answer: D — Fringe visibility decreases
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Q. What is the effect of increasing the wavelength of light in a double-slit experiment on the fringe separation?
A.
Fringe separation decreases
B.
Fringe separation increases
C.
Fringe separation remains the same
D.
Fringe separation becomes zero
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Solution
Fringe separation is directly proportional to the wavelength; increasing the wavelength increases the fringe separation.
Correct Answer: B — Fringe separation increases
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Q. What is the effect of increasing the wavelength of light on the fringe separation in a double-slit experiment?
A.
Increases
B.
Decreases
C.
No effect
D.
Depends on slit separation
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Solution
Fringe separation β = λD/d. Increasing λ increases β, hence fringe separation increases.
Correct Answer: A — Increases
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Q. What is the fringe width in a double-slit experiment if the wavelength of light is 500 nm, the distance between the slits is 0.2 mm, and the distance to the screen is 1 m?
A.
0.5 mm
B.
1 mm
C.
2 mm
D.
0.25 mm
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Solution
Fringe width β = λD/d = (500 x 10^-9 m)(1 m)/(0.2 x 10^-3 m) = 2.5 mm.
Correct Answer: A — 0.5 mm
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Q. What is the minimum thickness of a soap bubble for which the first order of bright fringe appears for light of wavelength 550 nm?
A.
275 nm
B.
550 nm
C.
1100 nm
D.
2200 nm
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Solution
For the first order bright fringe, thickness t = λ/2 = 550 nm / 2 = 275 nm.
Correct Answer: A — 275 nm
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Q. What is the minimum thickness of a soap bubble for which the first order of constructive interference occurs for light of wavelength 600 nm?
A.
100 nm
B.
200 nm
C.
300 nm
D.
400 nm
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Solution
For constructive interference in a soap bubble, the minimum thickness t = λ/2 = 600 nm / 2 = 300 nm.
Correct Answer: B — 200 nm
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Q. What is the minimum thickness of a soap bubble for which the first order of constructive interference occurs for light of wavelength 550 nm?
A.
275 nm
B.
550 nm
C.
1100 nm
D.
825 nm
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Solution
For constructive interference, the minimum thickness t = λ/2 = 550 nm / 2 = 275 nm.
Correct Answer: A — 275 nm
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Q. What is the minimum thickness of a soap bubble that will appear black when viewed in white light?
A.
λ/4
B.
λ/2
C.
λ
D.
3λ/4
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Solution
A soap bubble appears black when the thickness is λ/4 due to destructive interference of light reflected from the top and bottom surfaces.
Correct Answer: A — λ/4
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Q. What is the minimum thickness of a soap film that appears dark in reflected light for a wavelength of 600 nm?
A.
150 nm
B.
300 nm
C.
600 nm
D.
1200 nm
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Solution
For destructive interference in reflected light, the minimum thickness t = λ/2n, where n is the refractive index (approximately 1.5 for soap). Thus, t = 600 nm / (2 * 1.5) = 200 nm.
Correct Answer: B — 300 nm
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Q. What is the minimum thickness of a soap film that appears dark when viewed in reflected light?
A.
λ/4
B.
λ/2
C.
λ
D.
3λ/4
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Solution
For destructive interference in reflected light, the minimum thickness of the film must be λ/2.
Correct Answer: B — λ/2
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Q. What is the order of the first bright fringe in a single-slit diffraction pattern?
A.
m = 0
B.
m = 1
C.
m = 2
D.
m = 3
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Solution
In single-slit diffraction, the central maximum corresponds to m = 0, which is the first bright fringe.
Correct Answer: A — m = 0
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Q. What is the path difference for light waves from two coherent sources at an angle of 45° to the line joining the sources at a distance of 1 m?
A.
0.5 m
B.
0.707 m
C.
1 m
D.
0.25 m
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Solution
Path difference = d sin θ = 1 m * sin(45°) = 1 m * √2/2 = 0.707 m.
Correct Answer: B — 0.707 m
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Q. What is the path difference for light waves from two coherent sources at an angle of 45° to the line joining them?
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Solution
Path difference = d sin θ = d sin(45°) = d(√2/2). For d = λ, path difference = √2λ.
Correct Answer: C — √2λ
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Q. What is the path difference for the first minimum in a double-slit experiment?
A.
λ/2
B.
λ
C.
3λ/2
D.
2λ
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Solution
The path difference for the first minimum is λ/2, which leads to destructive interference.
Correct Answer: A — λ/2
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Q. What is the phase difference between two waves that are 180° out of phase?
A.
0
B.
90°
C.
180°
D.
360°
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Solution
A phase difference of 180° corresponds to the waves being out of phase, leading to destructive interference.
Correct Answer: C — 180°
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Q. What is the phase difference between two waves that interfere constructively?
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Solution
Constructive interference occurs when the phase difference is an integer multiple of 2π, which corresponds to a phase difference of 0.
Correct Answer: A — 0
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Q. What is the phase difference between two waves that interfere destructively?
A.
0 radians
B.
π/2 radians
C.
π radians
D.
3π/2 radians
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Solution
Destructive interference occurs when the phase difference is π radians (or an odd multiple of π).
Correct Answer: C — π radians
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Q. What is the phenomenon called when light waves bend around the edges of an obstacle?
A.
Reflection
B.
Refraction
C.
Diffraction
D.
Interference
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Solution
The bending of light waves around the edges of an obstacle is known as diffraction.
Correct Answer: C — Diffraction
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Q. What is the relationship between the angle of diffraction and the wavelength of light in a single-slit diffraction pattern?
A.
Directly proportional
B.
Inversely proportional
C.
No relationship
D.
Depends on slit width
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Solution
The angle of diffraction is inversely proportional to the wavelength; as the wavelength increases, the angle of diffraction increases.
Correct Answer: B — Inversely proportional
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Q. What is the relationship between the angle of incidence and the angle of diffraction in a diffraction grating?
A.
They are equal
B.
They are inversely proportional
C.
They are related by the grating equation
D.
They are independent
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Solution
The angle of incidence and angle of diffraction are related by the grating equation d sin(θ) = mλ.
Correct Answer: C — They are related by the grating equation
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Q. What is the relationship between the width of the central maximum and the wavelength in a single-slit diffraction pattern?
A.
Directly proportional
B.
Inversely proportional
C.
No relationship
D.
Exponential relationship
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Solution
The width of the central maximum is inversely proportional to the slit width and directly proportional to the wavelength.
Correct Answer: B — Inversely proportional
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Q. What is the result of light passing through a polarizer followed by an analyzer oriented at 90 degrees to the polarizer?
A.
All light passes through
B.
No light passes through
C.
Half the light passes through
D.
Light intensity is doubled
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Solution
When light passes through a polarizer and then an analyzer at 90 degrees, no light passes through due to the orthogonal orientation.
Correct Answer: B — No light passes through
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Q. What is the role of the phase change upon reflection in thin film interference?
A.
It enhances constructive interference
B.
It enhances destructive interference
C.
It has no effect
D.
It changes the wavelength
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Solution
A phase change of π (or half a wavelength) occurs upon reflection from a medium of higher refractive index, affecting the interference pattern.
Correct Answer: B — It enhances destructive interference
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Q. What is the wavelength of light if the first-order maximum occurs at an angle of 30° in a double-slit experiment with slit separation of 0.1 mm and a screen distance of 1 m?
A.
300 nm
B.
600 nm
C.
450 nm
D.
750 nm
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Solution
Using d sin θ = mλ, λ = d sin θ/m. For m=1, d=0.1 mm, θ=30°, λ = 0.1 mm * sin(30°) = 0.1 mm * 0.5 = 0.05 mm = 500 nm.
Correct Answer: B — 600 nm
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Q. What is the wavelength of light if the first-order maximum occurs at an angle of 30° in a double-slit experiment with slit separation of 0.1 mm and distance to screen of 1 m?
A.
0.5 mm
B.
0.3 mm
C.
0.2 mm
D.
0.1 mm
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Solution
Using d sin θ = mλ, λ = d sin θ/m. For m=1, d=0.1 mm, θ=30°, λ = 0.1 mm * sin(30°) = 0.1 mm * 0.5 = 0.05 mm = 0.2 mm.
Correct Answer: C — 0.2 mm
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