Optics
Q. A fiber optic cable uses total internal reflection. What is the role of the cladding?
A.
To increase the refractive index.
B.
To decrease the refractive index.
C.
To prevent light loss.
D.
To enhance light absorption.
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Solution
The cladding has a lower refractive index than the core, ensuring that light is kept within the core through total internal reflection.
Correct Answer: C — To prevent light loss.
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Q. A lens forms a real image of a height 5 cm at a distance of 40 cm from the lens. If the object is placed at 20 cm from the lens, what is the height of the object?
A.
2.5 cm
B.
5 cm
C.
10 cm
D.
20 cm
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Solution
Using the magnification formula, m = h'/h = -v/u. Here, h' = 5 cm, v = 40 cm, u = -20 cm. Thus, h = (h' * u) / v = (5 * -20) / 40 = 2.5 cm.
Correct Answer: C — 10 cm
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Q. A lens forms a real image of an object placed 60 cm away from it. If the image distance is 20 cm, what is the focal length of the lens?
A.
10 cm
B.
15 cm
C.
20 cm
D.
30 cm
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Solution
Using the lens formula 1/f = 1/v - 1/u, where u = -60 cm and v = 20 cm, we find f = 30 cm.
Correct Answer: D — 30 cm
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Q. A lens forms a real image of an object placed at a distance of 60 cm from it. If the image distance is 15 cm, what is the focal length of the lens?
A.
10 cm
B.
12 cm
C.
20 cm
D.
25 cm
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Solution
Using the lens formula 1/f = 1/v - 1/u, we have 1/f = 1/15 - 1/60. Solving gives f = 10 cm.
Correct Answer: A — 10 cm
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Q. A lens forms a real image that is three times the size of the object. If the object is placed 20 cm from the lens, what is the focal length of the lens?
A.
10 cm
B.
15 cm
C.
5 cm
D.
20 cm
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Solution
Using magnification m = -v/u = 3, we find v = -60 cm and then use the lens formula to find f = 15 cm.
Correct Answer: B — 15 cm
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Q. A lens forms a real image that is twice the size of the object. If the object is placed 10 cm from the lens, what is the focal length of the lens?
A.
5 cm
B.
10 cm
C.
15 cm
D.
20 cm
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Solution
Using the lens formula and magnification, we find the focal length to be 15 cm.
Correct Answer: C — 15 cm
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Q. A lens forms a virtual image at a distance of 10 cm when the object is placed at 5 cm. What type of lens is it?
A.
Convex lens
B.
Concave lens
C.
Bifocal lens
D.
Plano-convex lens
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Solution
A virtual image is formed by a concave lens when the object is placed within its focal length.
Correct Answer: B — Concave lens
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Q. A lens forms a virtual image at a distance of 12 cm when the object is placed at 8 cm. What is the focal length of the lens?
A.
4 cm
B.
6 cm
C.
8 cm
D.
10 cm
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Solution
Using the lens formula, 1/f = 1/v - 1/u, we find f = 4 cm.
Correct Answer: A — 4 cm
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Q. A lens forms a virtual image at a distance of 20 cm from the lens when the object is placed at 10 cm. What is the focal length of 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, where v = -20 cm and u = -10 cm, we find f = 5 cm.
Correct Answer: A — 5 cm
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Q. A lens forms a virtual image at a distance of 20 cm when the object is placed at 10 cm. What is the type of lens?
A.
Convex lens
B.
Concave lens
C.
Bifocal lens
D.
Plano-convex lens
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Solution
A virtual image formed by a lens indicates that it is a concave lens.
Correct Answer: B — Concave lens
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Q. A lens has a focal length of +20 cm. What type of lens is it?
A.
Concave lens
B.
Convex lens
C.
Bifocal lens
D.
Cylindrical lens
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Solution
A positive focal length indicates that the lens is a convex lens, which converges light rays.
Correct Answer: B — Convex lens
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Q. A lens has a focal length of -10 cm. What type of lens is it?
A.
Convex lens
B.
Concave lens
C.
Biconvex lens
D.
Biconcave lens
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Solution
A negative focal length indicates that the lens is a concave lens.
Correct Answer: B — Concave lens
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Q. A lens has a focal length of 50 cm. If an object is placed at 100 cm, what type of image is formed?
A.
Real and inverted
B.
Virtual and erect
C.
Real and erect
D.
Virtual and inverted
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Solution
Since the object distance is greater than the focal length, a real and inverted image is formed.
Correct Answer: A — Real and inverted
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Q. A lens has a power of +2 diopters. What is its focal length?
A.
0.5 m
B.
1 m
C.
2 m
D.
3 m
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Solution
Power (P) is given by P = 1/f (in meters). Thus, f = 1/P = 1/2 = 0.5 m.
Correct Answer: B — 1 m
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Q. A lens has a power of +2.0 D. What is its focal length?
A.
50 cm
B.
25 cm
C.
20 cm
D.
10 cm
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Solution
Power (P) = 1/f (in meters), so f = 1/2.0 = 0.5 m = 50 cm.
Correct Answer: B — 25 cm
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Q. A lens has a power of +2.5 D. What is its focal length?
A.
40 cm
B.
25 cm
C.
50 cm
D.
20 cm
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Solution
Power (P) = 1/f (in meters). Therefore, f = 1/2.5 = 0.4 m = 40 cm.
Correct Answer: B — 25 cm
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Q. A lens has a power of +2.5 D. What is the focal length of the lens in meters?
A.
0.4 m
B.
0.5 m
C.
0.6 m
D.
0.7 m
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Solution
Power (P) = 1/f, so f = 1/P = 1/2.5 = 0.4 m.
Correct Answer: B — 0.5 m
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Q. A lens has a power of +5 diopters. What is its focal length?
A.
20 cm
B.
25 cm
C.
30 cm
D.
15 cm
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Solution
Power (P) = 1/f (in meters). Therefore, f = 1/P = 1/5 = 0.2 m = 20 cm.
Correct Answer: A — 20 cm
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Q. A lens has a power of -4 D. What is the type of lens?
A.
Convex
B.
Concave
C.
Bifocal
D.
Plano-convex
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Solution
A negative power indicates a concave lens.
Correct Answer: B — Concave
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Q. A lens has a power of -4 D. What type of lens is it?
A.
Convex lens
B.
Concave lens
C.
Bifocal lens
D.
Plano-convex lens
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Solution
A negative power indicates that the lens is a concave lens.
Correct Answer: B — Concave lens
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Q. A lens produces a magnification of 3. If the object height is 2 cm, what is the image height?
A.
4 cm
B.
6 cm
C.
3 cm
D.
2 cm
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Solution
Magnification (m) = h'/h, thus h' = m * h = 3 * 2 = 6 cm.
Correct Answer: A — 4 cm
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Q. A lens produces a virtual image at a distance of 12 cm when the object is placed at 8 cm. What type of lens is it?
A.
Convex
B.
Concave
C.
Biconvex
D.
Biconcave
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Solution
A virtual image is formed by a concave lens when the object is placed in front of it.
Correct Answer: B — Concave
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Q. A light ray enters a glass prism with a refractive index of 1.5. If the angle of incidence is 30 degrees, what is the angle of refraction?
A.
15 degrees
B.
20 degrees
C.
25 degrees
D.
30 degrees
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Solution
Using Snell's law, n1 * sin(i) = n2 * sin(r). Here, n1 = 1 (air), n2 = 1.5, i = 30 degrees. Solving gives r = 19.2 degrees.
Correct Answer: B — 20 degrees
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Q. A light ray in glass (n=1.5) strikes the boundary with air at an angle of 30°. Will it undergo total internal reflection?
A.
Yes
B.
No
C.
Depends on the angle
D.
Not enough information
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Solution
Since the angle of incidence is less than the critical angle (θc = sin⁻¹(1/1.5) ≈ 41.8°), it will not undergo total internal reflection.
Correct Answer: B — No
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Q. A light ray passes from air into glass with a refractive index of 1.5. If the angle of incidence is 30 degrees, what is the angle of refraction?
A.
18.4 degrees
B.
20 degrees
C.
22 degrees
D.
25 degrees
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Solution
Using Snell's law, n1 * sin(theta1) = n2 * sin(theta2). Here, n1 = 1 (air), n2 = 1.5 (glass), and theta1 = 30 degrees. Thus, sin(theta2) = (1 * sin(30))/1.5 = 0.333, giving theta2 ≈ 19.1 degrees.
Correct Answer: A — 18.4 degrees
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Q. A light ray passes through the center of curvature of a concave mirror. What will be the angle of reflection?
A.
0 degrees
B.
30 degrees
C.
45 degrees
D.
90 degrees
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Solution
When a light ray passes through the center of curvature, it strikes the mirror perpendicularly, resulting in an angle of reflection of 0 degrees.
Correct Answer: A — 0 degrees
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Q. A light ray strikes a glass slab at an angle of incidence of 45 degrees. If the refractive index of glass is 1.5, what is the angle of refraction?
A.
30 degrees
B.
45 degrees
C.
60 degrees
D.
90 degrees
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Solution
Using Snell's law, n1 * sin(i) = n2 * sin(r). Here, sin(r) = (1 * sin(45)) / 1.5 = 0.471, giving r ≈ 28 degrees.
Correct Answer: A — 30 degrees
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Q. A light ray strikes a glass surface at an angle of 60 degrees. If the refractive index of glass is 1.5, what is the angle of refraction?
A.
30 degrees
B.
40 degrees
C.
60 degrees
D.
90 degrees
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Solution
Using Snell's law, n1 * sin(i) = n2 * sin(r). Here, n1 = 1 (air), n2 = 1.5 (glass), i = 60 degrees. Solving gives r = 40 degrees.
Correct Answer: B — 40 degrees
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Q. A light ray strikes a glass surface at an angle of incidence of 30 degrees. If the refractive index of glass is 1.5, what is the angle of refraction?
A.
20 degrees
B.
30 degrees
C.
40 degrees
D.
50 degrees
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Solution
Using Snell's law, n1 * sin(θ1) = n2 * sin(θ2). Here, n1 = 1 (air), θ1 = 30 degrees, n2 = 1.5. Thus, sin(θ2) = (1 * sin(30))/1.5 = 1/3, giving θ2 ≈ 20 degrees.
Correct Answer: A — 20 degrees
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Q. A light ray strikes a plane mirror at an angle of 45 degrees. What is the angle of reflection?
A.
0 degrees
B.
45 degrees
C.
90 degrees
D.
30 degrees
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Solution
According to the law of reflection, the angle of reflection equals the angle of incidence, so it is 45 degrees.
Correct Answer: B — 45 degrees
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