Optics
Q. In a thin film of oil on water, which color will appear bright if the film thickness is such that destructive interference occurs for blue light?
A.
Red
B.
Green
C.
Blue
D.
Yellow
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Solution
If destructive interference occurs for blue light, the complementary color (red) will appear bright.
Correct Answer: A — Red
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Q. In a thin film of oil on water, which color will be most prominently seen due to constructive interference?
A.
Red
B.
Blue
C.
Green
D.
Yellow
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Solution
Constructive interference in thin films often enhances the green color due to the specific thickness of the film and the wavelength of light.
Correct Answer: C — Green
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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. In a thin film of oil on water, which phenomenon is responsible for the colorful patterns observed?
A.
Diffraction
B.
Refraction
C.
Interference
D.
Reflection
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Solution
The colorful patterns in a thin film are due to interference of light waves reflected from the top and bottom surfaces of the film.
Correct Answer: C — Interference
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Q. In a thin film of soap, if the refractive index is 1.33 and the wavelength of light in air is 500 nm, what is the effective wavelength in the film?
A.
375 nm
B.
500 nm
C.
600 nm
D.
750 nm
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Solution
Effective wavelength in the film = λ/n = 500 nm / 1.33 ≈ 375 nm.
Correct Answer: A — 375 nm
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Q. In a thin film of soap, why do we see different colors when viewed at different angles?
A.
Due to diffraction
B.
Due to varying thickness of the film
C.
Due to reflection only
D.
Due to absorption of light
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Solution
Different colors are seen due to interference of light waves reflected from different thicknesses of the soap film, which changes with angle.
Correct Answer: B — Due to varying thickness of the film
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Q. In a thin film of soap, why do we see different colors?
A.
Different wavelengths interfere constructively at different angles
B.
Different wavelengths are absorbed
C.
Different wavelengths reflect differently
D.
Different wavelengths travel at different speeds
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Solution
Different colors are seen because different wavelengths of light interfere constructively at different angles due to the varying thickness of the soap film.
Correct Answer: A — Different wavelengths interfere constructively at different angles
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Q. In a thin lens, if the object distance is 15 cm and the image distance is 10 cm, what is the magnification?
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Solution
Magnification (m) is given by m = -v/u. Here, m = -10/15 = -2/3, which means the magnification is 1.5 in absolute value.
Correct Answer: B — 1.5
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Q. In a total internal reflection scenario, if the angle of incidence is 45° and the refractive index of the medium is 1.5, what is the angle of refraction?
A.
45°
B.
30°
C.
60°
D.
Total internal reflection occurs
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Solution
Since the angle of incidence (45°) is less than the critical angle (approximately 41.8° for glass to air), total internal reflection does not occur, and the angle of refraction cannot be calculated.
Correct Answer: D — Total internal reflection occurs
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Q. In a total internal reflection, what is the minimum angle of incidence for light traveling from water to air?
A.
30 degrees
B.
45 degrees
C.
60 degrees
D.
90 degrees
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Solution
The critical angle for water to air is approximately 48.6 degrees. Therefore, the minimum angle of incidence is 60 degrees.
Correct Answer: C — 60 degrees
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Q. In a two-slit interference pattern, if the angle of the first order maximum is θ, what is the path difference?
A.
λ
B.
2λ
C.
λ sin θ
D.
2λ sin θ
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Solution
The path difference for the first order maximum is given by d sin θ = λ, hence the path difference is λ sin θ.
Correct Answer: C — λ sin θ
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Q. In a two-slit interference pattern, if the distance between the slits is increased, what happens to the fringe separation?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes zero
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Solution
Increasing the distance between the slits (d) decreases the fringe separation, as fringe separation is inversely proportional to d.
Correct Answer: B — Decreases
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Q. In a two-slit interference pattern, if the distance between the slits is increased, what happens to the number of visible fringes on the screen?
A.
Increases
B.
Decreases
C.
Remains the same
D.
Becomes zero
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Solution
Increasing the distance between the slits (d) decreases the fringe width, which in turn reduces the number of visible fringes on the screen.
Correct Answer: B — Decreases
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Q. In a two-slit interference pattern, if the distance to the screen is doubled, what happens to the fringe spacing?
A.
It doubles
B.
It halves
C.
It remains the same
D.
It quadruples
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Solution
Fringe spacing (β) is directly proportional to the distance to the screen (D). If D is doubled, the fringe spacing also doubles.
Correct Answer: A — It doubles
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Q. In a two-slit interference pattern, if the intensity at the center is I0, what is the intensity at the first minimum?
A.
0
B.
I0
C.
I0/2
D.
I0/4
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Solution
At the first minimum, the intensity is 0 due to destructive interference.
Correct Answer: A — 0
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Q. In a two-slit interference pattern, if the intensity at the center is I_0, what is the intensity at the first minimum?
A.
0
B.
I_0
C.
I_0/2
D.
I_0/4
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Solution
At the first minimum, the intensity is 0 due to destructive interference.
Correct Answer: A — 0
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Q. In a two-slit interference pattern, if the intensity of light from one slit is increased, what happens to the overall intensity of the pattern?
A.
It decreases
B.
It remains the same
C.
It increases
D.
It becomes zero
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Solution
Increasing the intensity from one slit increases the overall intensity of the interference pattern.
Correct Answer: C — It increases
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Q. In double-slit diffraction, what is the effect of increasing the distance between the slits on the fringe width?
A.
Fringe width increases
B.
Fringe width decreases
C.
Fringe width remains constant
D.
Fringe width becomes zero
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Solution
Increasing the distance between the slits increases the fringe width because the angle of diffraction increases.
Correct Answer: A — Fringe width increases
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Q. In double-slit diffraction, what is the path difference for constructive interference at the first order maximum?
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Solution
For constructive interference, the path difference must be an integer multiple of the wavelength, so for the first order maximum, it is λ.
Correct Answer: B — λ
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Q. In optical fibers, total internal reflection is utilized. What is the primary reason for this?
A.
To increase the speed of light.
B.
To minimize loss of light.
C.
To change the color of light.
D.
To focus light.
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Solution
Total internal reflection in optical fibers minimizes the loss of light as it allows light to be guided through the fiber with minimal attenuation.
Correct Answer: B — To minimize loss of light.
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Q. In the context of diffraction, what does the term 'angular width' refer to?
A.
The angle between the first and second minima
B.
The angle of incidence
C.
The angle of reflection
D.
The angle of diffraction
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Solution
Angular width refers to the angle between the first and second minima in a diffraction pattern.
Correct Answer: A — The angle between the first and second minima
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Q. In the context of diffraction, what does the term 'coherence' refer to?
A.
The ability of waves to interfere
B.
The speed of light
C.
The intensity of light
D.
The wavelength of light
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Solution
Coherence refers to the ability of waves to maintain a constant phase relationship, which is essential for producing clear interference patterns.
Correct Answer: A — The ability of waves to interfere
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Q. In the context of diffraction, what does the term 'resolution' refer to?
A.
The ability to distinguish between two closely spaced objects
B.
The intensity of the diffracted light
C.
The wavelength of the light used
D.
The width of the slit
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Solution
Resolution refers to the ability to distinguish between two closely spaced objects, which is affected by diffraction.
Correct Answer: A — The ability to distinguish between two closely spaced objects
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Q. In thin film interference, if the refractive index of the film is greater than that of the surrounding medium, what happens to the phase of the reflected wave?
A.
No phase change
B.
Phase change of π
C.
Phase change of 2π
D.
Phase change of λ
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Solution
When light reflects off a denser medium, it undergoes a phase change of π (180 degrees).
Correct Answer: B — Phase change of π
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Q. In thin film interference, what causes a phase change of π?
A.
Reflection from a denser medium
B.
Reflection from a rarer medium
C.
Transmission through a denser medium
D.
Transmission through a rarer medium
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Solution
A phase change of π occurs when a wave reflects off a denser medium.
Correct Answer: A — Reflection from a denser medium
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Q. In thin film interference, what happens to the colors observed when the thickness of the film increases?
A.
Colors become brighter
B.
Colors change
C.
Colors disappear
D.
Colors remain the same
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Solution
As the thickness of the film increases, the path difference changes, leading to a change in the observed colors due to interference.
Correct Answer: B — Colors change
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Q. In which of the following scenarios does light become polarized by reflection?
A.
When it passes through a prism
B.
When it reflects off a smooth surface at a specific angle
C.
When it travels through a foggy medium
D.
When it is diffracted through a narrow slit
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Solution
Light becomes polarized by reflection when it reflects off a smooth surface at Brewster's angle.
Correct Answer: B — When it reflects off a smooth surface at a specific angle
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Q. In which of the following scenarios does light become polarized?
A.
When it passes through a prism
B.
When it reflects off a non-metallic surface
C.
When it travels through a vacuum
D.
When it diffracts through a slit
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Solution
Light becomes polarized when it reflects off a non-metallic surface, as the reflected light tends to align in a particular direction.
Correct Answer: B — When it reflects off a non-metallic surface
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Q. In which of the following scenarios is light most likely to be polarized?
A.
When it passes through a prism
B.
When it reflects off a smooth surface
C.
When it travels through a vacuum
D.
When it diffracts through a narrow slit
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Solution
Light is most likely to be polarized when it reflects off a smooth surface, such as water or glass.
Correct Answer: B — When it reflects off a smooth surface
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Q. In which of the following scenarios is light polarized?
A.
Light from a candle
B.
Light from a laser
C.
Light from an incandescent bulb
D.
Light from a fluorescent lamp
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Solution
Light from a laser is typically polarized, while the other sources emit unpolarized light.
Correct Answer: B — Light from a laser
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