The radius of curvature of a convex mirror of focal length 20 cm is MCQ with Answer and Explanation

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The radius of curvature of a convex mirror of focal length 20 cm is

A. 20 cm

B. 40 cm

C. 10 cm

D. 30 cm

Answer: Option B

Solution (By JKSSB Mock Tests)

R = 2f = 40 cm. For convex, f positive, R positive.

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Question #1

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Two resistors in series have equivalent 6 Ω, in parallel 4/3 Ω. Individual resistors are

A. 1 Ω and 5 Ω

B. 3 Ω and 3 Ω

C. 2 Ω and 2 Ω

D. 2 Ω and 4 Ω

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Correct Answer: Option D

Explanation:
Series: R1+R2=6. Parallel: (R1×R2)/(6)=4/3 => R1R2=8. Solving: R1,R2 = 2,4.

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Question #2

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The power of a lens is measured in

A. Metre

B. Watt

C. Lux

D. Dioptre

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Correct Answer: Option D

Explanation:
Dioptre (D) = m⁻¹. Power = 1/f in metres. Convex positive, concave negative. Optometry uses dioptre.

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Question #3

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Identify the incorrect statement regarding the human eye.

A. The cornea provides most of the eye's refractive power.

B. The retina acts as the screen where images are formed.

C. The image formed on the retina is virtual and erect.

D. The pupil regulates the amount of light entering the eye.

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Correct Answer: Option C

Explanation:
The eye lens is a convex (converging) lens. It converges light rays to form a real and inverted image on the retina. The brain processes this signal and flips it so we perceive the world as erect. All other statements are functionally correct. The cornea does indeed do about two-thirds of the focusing.

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