Optics
Q. If the focal length of a lens is -10 cm, what type of lens is it?
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A.
Convex lens
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B.
Concave lens
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C.
Bifocal lens
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D.
Cylindrical lens
Solution
A negative focal length indicates that the lens is a concave lens.
Correct Answer: B — Concave lens
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Q. If the focal length of a lens is 20 cm, what is the power of the lens?
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A.
+5 D
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B.
+10 D
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C.
-5 D
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D.
-10 D
Solution
Power (P) = 1/f (in meters). Here, f = 0.2 m, so P = 1/0.2 = +5 D.
Correct Answer: B — +10 D
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Q. If the focal length of a lens is 25 cm, what is the power of the lens?
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A.
+2 D
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B.
+4 D
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C.
+5 D
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D.
+10 D
Solution
Power (P) is given by P = 1/f (in meters). Thus, P = 1/0.25 m = +4 D.
Correct Answer: C — +5 D
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Q. If the focal length of a lens is doubled, how does the power of the lens change?
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A.
Doubles
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B.
Halves
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C.
Remains the same
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D.
Quadruples
Solution
Power is inversely proportional to focal length. If f is doubled, P = 1/f will halve.
Correct Answer: B — Halves
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Q. If the image distance is equal to the object distance for a lens, what is the magnification?
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A.
0
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B.
1
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C.
2
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D.
Infinity
Solution
Magnification (m) = v/u = 1 when image distance equals object distance.
Correct Answer: B — 1
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Q. If the image distance of a convex lens is 40 cm and the object distance is 30 cm, what is the focal length of the lens?
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A.
10 cm
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B.
20 cm
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C.
30 cm
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D.
15 cm
Solution
Using the lens formula 1/f = 1/v - 1/u, we have 1/f = 1/40 - 1/(-30) = 1/40 + 1/30. Solving gives f = 20 cm.
Correct Answer: B — 20 cm
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Q. If the intensity of light at a point of constructive interference is I, what is the intensity at a point of destructive interference?
Solution
At destructive interference, the intensity is zero because the waves cancel each other out.
Correct Answer: B — 0
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Q. If the object distance is equal to the focal length of a convex lens, what is the nature of the image formed?
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A.
Real and inverted
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B.
Virtual and upright
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C.
At infinity
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D.
No image formed
Solution
When the object distance equals the focal length, the image is formed at infinity.
Correct Answer: C — At infinity
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Q. If the object distance is equal to the focal length of a convex lens, what type of image is formed?
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A.
Real and inverted
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B.
Virtual and upright
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C.
At infinity
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D.
No image formed
Solution
When the object is at the focal length, the image is formed at infinity.
Correct Answer: C — At infinity
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Q. If the radius of curvature of a concave mirror is 40 cm, what is its focal length?
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A.
10 cm
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B.
20 cm
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C.
30 cm
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D.
40 cm
Solution
The focal length f of a mirror is given by f = R/2. Thus, f = 40 cm / 2 = 20 cm.
Correct Answer: B — 20 cm
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Q. If the radius of curvature of a convex mirror is 30 cm, what is its focal length?
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A.
10 cm
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B.
15 cm
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C.
20 cm
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D.
30 cm
Solution
The focal length f of a mirror is given by f = R/2. For a convex mirror, R = 30 cm, so f = 30/2 = 15 cm.
Correct Answer: B — 15 cm
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Q. If the radius of curvature of a lens is 20 cm, what is the focal length of the lens assuming it is made of glass with a refractive index of 1.5?
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A.
10 cm
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B.
15 cm
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C.
20 cm
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D.
30 cm
Solution
Using the lens maker's formula, f = R/(n-1) = 20/(1.5-1) = 40 cm.
Correct Answer: A — 10 cm
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Q. If the radius of curvature of a lens is 30 cm and the refractive index is 1.5, what is the focal length of the lens?
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A.
10 cm
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B.
15 cm
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C.
20 cm
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D.
25 cm
Solution
Using the lens maker's formula, f = R/(n-1) = 30/(1.5-1) = 30/0.5 = 60 cm.
Correct Answer: B — 15 cm
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Q. If the radius of curvature of a lens is 30 cm, what is the focal length of the lens assuming it is made of glass with a refractive index of 1.5?
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A.
10 cm
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B.
15 cm
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C.
20 cm
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D.
25 cm
Solution
Using the lens maker's formula, f = R/(n-1) = 30/(1.5-1) = 30/0.5 = 60 cm.
Correct Answer: B — 15 cm
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Q. If the radius of curvature of a spherical mirror is 30 cm, what is its focal length?
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A.
10 cm
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B.
15 cm
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C.
20 cm
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D.
30 cm
Solution
Focal length f = R/2 = 30 cm / 2 = 15 cm.
Correct Answer: B — 15 cm
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Q. If the radius of curvature of a spherical mirror is 40 cm, what is its focal length?
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A.
10 cm
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B.
20 cm
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C.
30 cm
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D.
40 cm
Solution
The focal length (f) of a spherical mirror is given by f = R/2. Here, R = 40 cm, so f = 40/2 = 20 cm.
Correct Answer: B — 20 cm
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Q. If the refractive index of a medium is 1.33, what is the critical angle for total internal reflection?
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A.
48.6°
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B.
60.0°
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C.
30.0°
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D.
45.0°
Solution
Critical angle θc = sin⁻¹(1/1.33) ≈ 48.6°.
Correct Answer: A — 48.6°
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Q. If the refractive index of a medium is 1.33, what is the maximum angle of incidence for total internal reflection when light travels to air?
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A.
41.8°
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B.
48.6°
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C.
53.1°
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D.
60.0°
Solution
The critical angle θc can be calculated as θc = sin^(-1)(n2/n1) = sin^(-1)(1.00/1.33) ≈ 48.6°.
Correct Answer: A — 41.8°
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Q. If the refractive index of a medium is 1.33, what is the speed of light in that medium if the speed of light in vacuum is 3 x 10^8 m/s?
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A.
2.25 x 10^8 m/s
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B.
2.5 x 10^8 m/s
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C.
2.75 x 10^8 m/s
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D.
3 x 10^8 m/s
Solution
Speed of light in medium = c/n = (3 x 10^8 m/s) / 1.33 ≈ 2.25 x 10^8 m/s.
Correct Answer: A — 2.25 x 10^8 m/s
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Q. If the refractive index of a medium is 1.5, what is the maximum angle of incidence for total internal reflection when light travels to air?
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A.
41.8°
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B.
48.6°
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C.
60.0°
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D.
90.0°
Solution
The critical angle θc is given by sin(θc) = n2/n1 = 1/1.5, which gives θc ≈ 41.8°.
Correct Answer: A — 41.8°
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Q. If the refractive index of a medium is 1.5, what is the speed of light in that medium?
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A.
2 x 10^8 m/s
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B.
3 x 10^8 m/s
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C.
1.5 x 10^8 m/s
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D.
4.5 x 10^8 m/s
Solution
The speed of light in a medium is given by v = c/n. Here, c = 3 x 10^8 m/s and n = 1.5, so v = 3 x 10^8 / 1.5 = 2 x 10^8 m/s.
Correct Answer: A — 2 x 10^8 m/s
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Q. If the refractive index of a medium is 1.5, what is the speed of light in that medium? (Speed of light in vacuum = 3 x 10^8 m/s)
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A.
2 x 10^8 m/s
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B.
1.5 x 10^8 m/s
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C.
3 x 10^8 m/s
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D.
4.5 x 10^8 m/s
Solution
Speed of light in medium = c/n = (3 x 10^8 m/s) / 1.5 = 2 x 10^8 m/s.
Correct Answer: A — 2 x 10^8 m/s
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Q. If the refractive index of a medium is 1.5, what is the wavelength of light in that medium if the wavelength in vacuum is 600 nm?
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A.
400 nm
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B.
600 nm
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C.
800 nm
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D.
900 nm
Solution
Wavelength in medium = λ/v = λ0/n = 600 nm / 1.5 = 400 nm.
Correct Answer: A — 400 nm
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Q. If the refractive index of a medium is 2.0, what is the critical angle for total internal reflection?
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A.
30°
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B.
45°
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C.
60°
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D.
90°
Solution
Using the formula θc = sin^(-1)(1/n), where n = 2.0, we find θc = sin^(-1)(1/2) = 30°.
Correct Answer: C — 60°
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Q. If the refractive index of a medium is 2.0, what is the critical angle for total internal reflection at the interface with air?
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A.
30°
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B.
45°
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C.
60°
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D.
90°
Solution
Using the formula sin(θc) = n2/n1, we have sin(θc) = 1.00/2.00, leading to θc ≈ 30°.
Correct Answer: C — 60°
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Q. If the refractive index of a medium is 2.0, what is the critical angle for total internal reflection when light travels from this medium to air?
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A.
30°
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B.
45°
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C.
60°
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D.
90°
Solution
Using the formula sin(θc) = n2/n1, where n1 = 2.0 (medium) and n2 = 1.0 (air), we find sin(θc) = 1.0/2.0 = 0.5, leading to θc = 60°.
Correct Answer: C — 60°
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Q. If the refractive index of a medium is 2.0, what is the maximum angle of incidence for total internal reflection when light travels to air?
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A.
30°
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B.
45°
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C.
60°
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D.
90°
Solution
Critical angle θc = sin⁻¹(n2/n1) = sin⁻¹(1.00/2.00) ≈ 30°; thus, maximum angle of incidence for total internal reflection is 60°.
Correct Answer: C — 60°
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Q. If the refractive index of a medium is greater than 1, how does it affect the speed of light in that medium?
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A.
Increases speed
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B.
Decreases speed
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C.
No effect
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D.
Depends on wavelength
Solution
The speed of light in a medium is given by v = c/n, where n is the refractive index. If n > 1, the speed decreases.
Correct Answer: B — Decreases speed
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Q. If the refractive index of a medium is greater than 1, what happens to the speed of light in that medium compared to vacuum?
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A.
It increases
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B.
It decreases
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C.
It remains the same
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D.
It becomes infinite
Solution
The speed of light in a medium is less than that in vacuum, given by v = c/n, where n > 1.
Correct Answer: B — It decreases
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Q. If the refractive index of a medium is greater than 1, what happens to the speed of light in that medium?
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A.
It increases
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B.
It decreases
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C.
It remains the same
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D.
It becomes infinite
Solution
The speed of light in a medium is given by v = c/n, where n is the refractive index. If n > 1, then v < c, meaning the speed decreases.
Correct Answer: B — It decreases
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