Optics
Q. What is the focal length of a concave mirror if an object placed 30 cm in front of it produces an image at 10 cm in front of the mirror?
A.
5 cm
B.
10 cm
C.
15 cm
D.
20 cm
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Solution
Using the mirror formula 1/f = 1/v + 1/u, where u = -30 cm and v = -10 cm, we find f = 15 cm.
Correct Answer: C — 15 cm
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Q. What is the focal length of a concave mirror if an object placed at a distance of 30 cm produces an image at a distance of 15 cm?
A.
10 cm
B.
15 cm
C.
20 cm
D.
25 cm
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Solution
Using the mirror formula, 1/f = 1/v + 1/u; here, v = -15 cm (real image) and u = -30 cm. Thus, 1/f = 1/(-15) + 1/(-30) = -1/10, so f = 10 cm.
Correct Answer: A — 10 cm
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Q. What is the focal length of a convex lens if it forms a real image at a distance of 30 cm when the object is placed at 15 cm from the lens?
A.
10 cm
B.
15 cm
C.
20 cm
D.
25 cm
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Solution
Using the lens formula 1/f = 1/v - 1/u, where v = 30 cm and u = -15 cm, we find f = 20 cm.
Correct Answer: C — 20 cm
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Q. What is the focal length of a lens if it forms a virtual image at a distance of 15 cm when the object is placed at 10 cm?
A.
-30 cm
B.
30 cm
C.
15 cm
D.
10 cm
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Solution
Using the lens formula 1/f = 1/v - 1/u, we have 1/f = 1/(-15) - 1/(-10) = -1/15 + 1/10 = -1/30, thus f = -30 cm.
Correct Answer: A — -30 cm
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Q. What is the focal length of a lens if it forms a virtual image at a distance of 12 cm when the object is placed at 8 cm?
A.
-24 cm
B.
-12 cm
C.
12 cm
D.
24 cm
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Solution
Using the lens formula, we find the focal length to be -12 cm.
Correct Answer: B — -12 cm
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Q. What is the focal length of a lens if it forms an image at infinity when the object is placed at 30 cm?
A.
30 cm
B.
15 cm
C.
60 cm
D.
20 cm
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Solution
For the image to be at infinity, the focal length must be equal to the object distance, hence f = 60 cm.
Correct Answer: C — 60 cm
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Q. What is the focal length of a lens that forms a virtual image at a distance of 20 cm when the object is placed at 10 cm?
A.
5 cm
B.
10 cm
C.
15 cm
D.
20 cm
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Solution
Using the lens formula, 1/f = 1/v - 1/u. Here, v = -20 cm (virtual image), u = -10 cm. Solving gives f = 5 cm.
Correct Answer: A — 5 cm
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Q. What is the focal length of a plano-convex lens with a radius of curvature of 30 cm?
A.
15 cm
B.
30 cm
C.
45 cm
D.
60 cm
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Solution
Using the lens maker's formula for a plano-convex lens, f = R/2 = 30 cm / 2 = 30 cm.
Correct Answer: B — 30 cm
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Q. What is the formula for the angular position of the first minimum in a double-slit diffraction pattern?
A.
d sin(θ) = mλ
B.
d sin(θ) = (m + 1/2)λ
C.
d sin(θ) = (m - 1/2)λ
D.
d sin(θ) = 2mλ
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Solution
The angular position of the first minimum in a double-slit diffraction pattern is given by d sin(θ) = mλ, where m = 1 for the first minimum.
Correct Answer: A — d sin(θ) = mλ
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Q. What is the formula for the angular position of the m-th order maximum in a double-slit experiment?
A.
d sin θ = mλ
B.
d cos θ = mλ
C.
d tan θ = mλ
D.
d = mλ/sin θ
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Solution
The correct formula for the angular position of the m-th order maximum is d sin θ = mλ.
Correct Answer: A — d sin θ = mλ
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Q. What is the formula for the fringe separation in a double-slit experiment?
A.
λD/d
B.
d/λD
C.
D/λd
D.
λd/D
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Solution
The fringe separation (β) is given by the formula β = λD/d, where λ is the wavelength, D is the distance to the screen, and d is the distance between the slits.
Correct Answer: A — λD/d
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Q. What is the formula for the fringe width in a double-slit experiment?
A.
λD/d
B.
d/λD
C.
D/λd
D.
λd/D
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Solution
The fringe width (β) is given by the formula β = λD/d, where D is the distance from the slits to the screen and d is the distance between the slits.
Correct Answer: A — λD/d
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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 image distance for a concave lens with a focal length of -12 cm when the object is placed at 24 cm?
A.
-8 cm
B.
8 cm
C.
-12 cm
D.
12 cm
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Solution
Using the lens formula, 1/f = 1/v - 1/u, we find v = -8 cm.
Correct Answer: A — -8 cm
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Q. What is the image distance for a convex lens if the object is placed at 10 cm and the focal length is 5 cm?
A.
-15 cm
B.
15 cm
C.
5 cm
D.
10 cm
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Solution
Using the lens formula 1/f = 1/v - 1/u, we find v = 15 cm.
Correct Answer: A — -15 cm
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Q. What is the image distance for a convex lens if the object is placed at 30 cm and the focal length is 10 cm?
A.
15 cm
B.
20 cm
C.
25 cm
D.
30 cm
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Solution
Using the lens formula 1/f = 1/v - 1/u, we find v = 15 cm.
Correct Answer: B — 20 cm
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Q. What is the image distance for a convex lens with a focal length of 10 cm when the object is placed 30 cm from the lens?
A.
5 cm
B.
10 cm
C.
15 cm
D.
20 cm
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Solution
Using the lens formula 1/f = 1/v - 1/u, we find v = 20 cm.
Correct Answer: D — 20 cm
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Q. What is the magnification produced by a concave lens if the object distance is 20 cm and the image distance is -10 cm?
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Solution
Magnification m = -v/u = -(-10)/20 = 0.5.
Correct Answer: A — 0.5
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Q. What is the magnification produced by a concave mirror if the object is placed at a distance of 15 cm and the image is formed at 5 cm?
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Solution
Magnification (m) = -v/u = -(-5)/(-15) = 1/3. Therefore, the magnification is 3.
Correct Answer: C — 3
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Q. What is the magnification produced by a convex lens if the object is placed at twice the focal length?
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Solution
Magnification (m) = v/u. For an object at 2f, the image distance v = 2f, so m = 2f/(2f) = 1.
Correct Answer: A — 1
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Q. What is the magnification produced by a lens if the object distance is 15 cm and the image distance is 30 cm?
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Solution
Magnification (m) = image distance/object distance = 30/15 = 2.
Correct Answer: C — 2
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Q. What is the magnification produced by a lens if the object distance is 15 cm and the image distance is 45 cm?
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Solution
Magnification (m) = image distance/object distance = 45/15 = 3.
Correct Answer: C — 3
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Q. What is the magnification produced by a lens if the object distance is 20 cm and the image distance is 10 cm?
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Solution
Magnification (m) = -v/u = -10/20 = 0.5, but since we consider absolute value, m = 2.
Correct Answer: C — 2
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Q. What is the magnification produced by a lens if the object distance is 25 cm and the image distance is 50 cm?
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Solution
Magnification (m) = -v/u = -50/25 = -2. The absolute value indicates the image is twice the size of the object.
Correct Answer: C — 2
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Q. What is the main difference between diffraction and interference?
A.
Diffraction involves multiple sources, interference does not
B.
Interference involves multiple sources, diffraction does not
C.
Diffraction occurs with sound waves only
D.
Interference occurs with light waves only
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Solution
Interference involves the superposition of waves from multiple sources, while diffraction is the spreading of waves when they encounter an obstacle or aperture.
Correct Answer: B — Interference involves multiple sources, diffraction does not
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Q. What is the main reason for the appearance of a diffraction pattern when light passes through a narrow slit?
A.
Interference of light waves
B.
Refraction of light
C.
Absorption of light
D.
Reflection of light
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Solution
The diffraction pattern arises due to the interference of light waves that spread out after passing through the slit.
Correct Answer: A — Interference of light waves
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Q. What is the maximum intensity ratio in interference of two waves of equal amplitude?
A.
1:1
B.
2:1
C.
4:1
D.
3:1
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Solution
Maximum intensity (I_max) = 4I_0 for two waves of equal amplitude (I_0). Thus, the ratio is 4:1.
Correct Answer: C — 4:1
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Q. What is the maximum number of diffraction maxima that can be observed for a double-slit experiment with a slit separation of 0.1 mm and light of wavelength 500 nm?
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Solution
The maximum number of observable maxima is given by d/λ, where d = 0.1 mm and λ = 500 nm. This gives approximately 10 maxima.
Correct Answer: B — 10
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Q. What is the maximum percentage of light transmitted through two polarizers?
A.
0%
B.
25%
C.
50%
D.
100%
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Solution
The maximum percentage of light transmitted through two aligned polarizers is 100%.
Correct Answer: D — 100%
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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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