Optics Study Materials for Competitive Exam Preparation

Optics

Q. A beam of light passes from air into a medium with a refractive index of 1.5. If the angle of incidence is 30 degrees, what is the angle of refraction? (2022)

A. 19.1 degrees
B. 20 degrees
C. 25 degrees
D. 30 degrees

Solution

Using Snell's law, n1 * sin(i) = n2 * sin(r). Thus, sin(r) = (1 * sin(30)) / 1.5 = 0.333, giving r ≈ 19.1 degrees.

Correct Answer: A — 19.1 degrees

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Q. A beam of light passes through a prism with an angle of 60 degrees. If the refractive index of the prism is 1.5, what is the angle of deviation? (2023)

A. 30 degrees
B. 60 degrees
C. 45 degrees
D. 15 degrees

Solution

Using the formula for angle of deviation: D = A(n-1), we find D = 60(1.5-1) = 30 degrees.

Correct Answer: A — 30 degrees

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Q. A concave mirror has a focal length of 20 cm. What is the distance of the object from the mirror if the image formed is at a distance of 30 cm from the mirror? (2021)

A. 10 cm
B. 15 cm
C. 25 cm
D. 30 cm

Solution

Using the mirror formula: 1/f = 1/v + 1/u, where f = -20 cm (concave mirror), v = -30 cm (image distance), we find u = 25 cm.

Correct Answer: C — 25 cm

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Q. A concave mirror has a focal length of 20 cm. What is the radius of curvature of the mirror? (2021)

A. 10 cm
B. 20 cm
C. 30 cm
D. 40 cm

Solution

The radius of curvature (R) is twice the focal length (f). Therefore, R = 2f = 2 * 20 cm = 40 cm.

Correct Answer: B — 20 cm

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Q. A convex lens has a focal length of 20 cm. If an object is placed 60 cm from the lens, what is the position of the image?

A. 15 cm
B. 20 cm
C. 30 cm
D. 40 cm

Solution

Using the lens formula, 1/f = 1/v - 1/u, we find v = 30 cm.

Correct Answer: D — 40 cm

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Q. A convex lens has a focal length of 25 cm. What is the power of the lens? (2021)

A. +2 D
B. +4 D
C. +6 D
D. +8 D

Solution

Power (P) = 1/f (in meters). Thus, P = 1/0.25 = +4 D.

Correct Answer: B — +4 D

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Q. A lens forms a real image that is twice the size of the object. If the object distance is 10 cm, what is the image distance? (2021)

A. 10 cm
B. 15 cm
C. 20 cm
D. 25 cm

Solution

Using the magnification formula m = -v/u, where m = 2 and u = -10 cm, we find v = -2 * (-10) = 20 cm.

Correct Answer: C — 20 cm

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Q. A light ray strikes a glass surface at an angle 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

Solution

Using Snell's law, sin(r) = (n1/n2) * sin(i) = (1/1.5) * sin(45) = 0.471, giving r ≈ 30 degrees.

Correct Answer: A — 30 degrees

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Q. A plane mirror is placed at an angle of 60 degrees to the incident ray. What is the angle of reflection?

A. 30 degrees
B. 60 degrees
C. 90 degrees
D. 120 degrees

Solution

According to the law of reflection, the angle of reflection is equal to the angle of incidence. Therefore, the angle of reflection is also 60 degrees.

Correct Answer: B — 60 degrees

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Q. A ray of light strikes a plane mirror at an angle of 30 degrees to the normal. What is the angle of reflection? (2022)

A. 30 degrees
B. 45 degrees
C. 60 degrees
D. 90 degrees

Solution

According to the law of reflection, the angle of reflection is equal to the angle of incidence. Therefore, the angle of reflection is 30 degrees.

Correct Answer: A — 30 degrees

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Q. An object is placed 10 cm from a convex lens with a focal length of 5 cm. What is the nature of the image formed? (2022)

A. Real and inverted
B. Virtual and erect
C. Real and erect
D. Virtual and inverted

Solution

Since the object distance is less than the focal length, the image formed is virtual and erect.

Correct Answer: B — Virtual and erect

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Q. An object is placed 15 cm in front of a convex lens of focal length 10 cm. What is the position of the image formed? (2020)

A. 5 cm
B. 10 cm
C. 30 cm
D. 15 cm

Solution

Using the lens formula: 1/f = 1/v - 1/u, where f = 10 cm and u = -15 cm, we find v = 30 cm.

Correct Answer: C — 30 cm

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Q. An object is placed 30 cm in front of a convex lens of focal length 15 cm. What is the position of the image formed? (2020)

A. 10 cm
B. 15 cm
C. 20 cm
D. 25 cm

Solution

Using the lens formula 1/f = 1/v - 1/u, where u = -30 cm and f = 15 cm, we find v = 10 cm.

Correct Answer: D — 25 cm

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Q. An object is placed 30 cm in front of a convex lens of focal length 15 cm. What is the image distance?

A. 10 cm
B. 15 cm
C. 20 cm
D. 25 cm

Solution

Using the lens formula 1/f = 1/v - 1/u, where u = -30 cm and f = 15 cm, we find v = 10 cm.

Correct Answer: A — 10 cm

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Q. If a concave lens has a power of -5 D, what is its focal length? (2021)

A. -20 cm
B. -25 cm
C. -15 cm
D. -10 cm

Solution

Power P = 1/f, thus f = 1/P = 1/(-5) = -0.2 m = -20 cm.

Correct Answer: B — -25 cm

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Q. If the focal length of a convex lens is 25 cm, what is the power of the lens? (2023)

A. +2 D
B. +4 D
C. +5 D
D. +10 D

Solution

Power P = 1/f (in meters). Thus, P = 1/0.25 = +4 D.

Correct Answer: C — +5 D

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Q. If the wavelength of light in vacuum is 600 nm, what is its wavelength in water (n = 1.33)? (2023)

A. 450 nm
B. 600 nm
C. 750 nm
D. 800 nm

Solution

Wavelength in medium = Wavelength in vacuum / n. Thus, λ = 600 nm / 1.33 ≈ 450 nm.

Correct Answer: A — 450 nm

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Q. What is the critical angle for a glass medium (n = 1.5) when light travels from glass to air? (2020)

A. 30 degrees
B. 41.8 degrees
C. 48.6 degrees
D. 60 degrees

Solution

Using the formula for critical angle: sin(c) = n2/n1, we find c = sin^(-1)(1/1.5) ≈ 41.8 degrees.

Correct Answer: B — 41.8 degrees

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Q. What is the critical angle for light traveling from glass (n = 1.5) to air (n = 1)? (2019)

A. 30 degrees
B. 41.8 degrees
C. 48.6 degrees
D. 60 degrees

Solution

Using the formula sin(c) = n2/n1, we find sin(c) = 1/1.5, thus c = sin^(-1)(2/3) ≈ 41.8 degrees.

Correct Answer: B — 41.8 degrees

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Q. What is the focal length of a diverging lens if the image distance is -15 cm and the object distance is -10 cm? (2023)

A. -30 cm
B. -20 cm
C. -15 cm
D. -10 cm

Solution

Using the lens formula 1/f = 1/v - 1/u, we find f = -20 cm.

Correct Answer: B — -20 cm

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Q. What is the magnification produced by a concave lens if the object is placed at a distance of 30 cm and the focal length of the lens is 15 cm? (2022)

A. -0.5
B. -1
C. -2
D. -3

Solution

Using the lens formula and magnification formula, we find the magnification m = -v/u = -1.

Correct Answer: B — -1

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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 focal length is 5 cm?

A. 1
B. 2
C. 3
D. 4

Solution

Using the mirror formula, 1/f = 1/v + 1/u, we find v = -7.5 cm. Magnification (m) = -v/u = 7.5/15 = 0.5.

Correct Answer: C — 3

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Optics

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