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Question (11)

QN0036282

A concave mirror has focal length -20 cm and an object is placed 50 cm in front of it. The image distance is approximately

(A) -33.3 cm
(B) +33.3 cm
(C) -16.7 cm
(D) +16.7 cm

Correct Answer: A

Explanation:

Using the mirror formula, 1/v = 1/f - 1/u = -1/20 + 1/50 = -3/100. Hence v ≈ -33.3 cm.

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Question (12)

QN0036283

An object 4 cm high is placed 50 cm in front of a concave mirror of focal length -20 cm. The approximate image height is

(A) +2.67 cm
(B) -2.67 cm
(C) +6 cm
(D) -6 cm

Correct Answer: B

Explanation:

From the previous calculation, v ≈ -33.3 cm. Thus m = -v/u ≈ -0.667 and h' = m × h ≈ -2.67 cm.

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Question (13)

QN0036284

A ray of light passing through the centre of curvature of a concave mirror

(A) bends towards the focus
(B) becomes parallel to the principal axis
(C) retraces its path after reflection
(D) passes through the pole

Correct Answer: C

Explanation:

A ray passing through the centre of curvature strikes the mirror normally and retraces its path after reflection.

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Question (14)

QN0036285

An object is placed 40 cm in front of a concave mirror having radius of curvature 50 cm. The image is

(A) virtual, erect and diminished
(B) real, inverted and enlarged
(C) real, erect and diminished
(D) virtual, inverted and enlarged

Correct Answer: B

Explanation:

The focal length is 25 cm. Since the object is between F and C, the image is real, inverted and enlarged.

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Question (15)

QN0036286

An object is placed 10 cm in front of a concave mirror of focal length 15 cm. The image formed is

(A) real and diminished
(B) real and same size
(C) virtual, erect and enlarged
(D) real, inverted and enlarged

Correct Answer: C

Explanation:

Since the object is between the pole and focus, the image is virtual, erect and enlarged.

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Question (16)

QN0036287

A spherical mirror has a focal length of +25 cm. The mirror is

(A) concave
(B) convex
(C) plane
(D) cylindrical

Correct Answer: B

Explanation:

Under the Cartesian sign convention, a positive focal length indicates a convex mirror.

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Question (17)

QN0036288

A convex mirror has a radius of curvature of 40 cm. An object is placed 60 cm in front of it. The image distance and magnification are

(A) +15 cm and +0.25
(B) -15 cm and -0.25
(C) +30 cm and +0.5
(D) -30 cm and -0.5

Correct Answer: A

Explanation:

f = R/2 = 20 cm. Using the mirror formula gives v = +15 cm. Hence m = -v/u = +0.25.

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Question (18)

QN0036289

When a ray of light travels obliquely from air into glass, it bends

(A) away from the normal
(B) towards the normal
(C) along the surface
(D) without changing direction

Correct Answer: B

Explanation:

Glass is optically denser than air, so an oblique ray bends towards the normal on entering glass.

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Question (19)

QN0036290

The speed of light in a medium is 2 × 10^8 m/s. Taking the speed of light in vacuum as 3 × 10^8 m/s, its refractive index is

(A) 0.67
(B) 1.0
(C) 1.5
(D) 2.0

Correct Answer: C

Explanation:

n = c/v = (3 × 10^8)/(2 × 10^8) = 1.5.

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Question (20)

QN0036291

Light travels through medium A at 2.4 × 10^8 m/s and through medium B at 1.8 × 10^8 m/s. The refractive index of B with respect to A is approximately

(A) 0.75
(B) 1.00
(C) 1.33
(D) 1.50

Correct Answer: C

Explanation:

nBA = speed in A/speed in B = 2.4/1.8 ≈ 1.33.

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Question (11)

A concave mirror has focal length -20 cm and an object is placed 50 cm in front of it. The image distance is approximately

Explanation:

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Question (12)

An object 4 cm high is placed 50 cm in front of a concave mirror of focal length -20 cm. The approximate image height is

Explanation:

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Question (13)

A ray of light passing through the centre of curvature of a concave mirror

Explanation:

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Question (14)

An object is placed 40 cm in front of a concave mirror having radius of curvature 50 cm. The image is

Explanation:

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Question (15)

An object is placed 10 cm in front of a concave mirror of focal length 15 cm. The image formed is

Explanation:

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Question (16)

A spherical mirror has a focal length of +25 cm. The mirror is

Explanation:

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Question (17)

A convex mirror has a radius of curvature of 40 cm. An object is placed 60 cm in front of it. The image distance and magnification are

Explanation:

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Question (18)

When a ray of light travels obliquely from air into glass, it bends

Explanation:

Link:

Question (19)

The speed of light in a medium is 2 × 10^8 m/s. Taking the speed of light in vacuum as 3 × 10^8 m/s, its refractive index is

Explanation:

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Question (20)

Light travels through medium A at 2.4 × 10^8 m/s and through medium B at 1.8 × 10^8 m/s. The refractive index of B with respect to A is approximately

Explanation:

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