A convex lens is placed in water. Its focal length MCQ with Answer and Explanation

A convex lens is placed in water. Its focal length
A. Becomes zero
B. Decreases
C. Increases
D. Remains same
Answer: Option C
Solution (By JKSSB Mock Tests)
Refractive index relative to water decreases, so power decreases, focal length increases.

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Practice More Physics Questions

Question #1
A machine gun fires n bullets per second, each of mass m with velocity v. The force on the gun is
A. nmv/t
B. ½ nmv
C. nmv²
D. nmv

Correct Answer: Option D


Explanation:
Force = rate of change of momentum = n × (mv) = nmv. This is average force required to hold gun.

This question belongs to: Science Physics
Question #2
A 60 W bulb operates at 120 V. Its resistance is
A. 240 Ω
B. 480 Ω
C. 60 Ω
D. 120 Ω

Correct Answer: Option A


Explanation:
R = V²/P = 14400/60 = 240 Ω.

This question belongs to: Science Physics
Question #3
Two masses, M1 = 3 kg and M2 = 2 kg, are connected by a light inextensible string passing over a frictionless pulley (Atwood machine). The acceleration of the system is (Take g = 10 m/s^2):
A. 2 m/s^2
B. 10 m/s^2
C. 5 m/s^2
D. 4 m/s^2

Correct Answer: Option A


Explanation:
For an Atwood machine, the common acceleration of both masses is given by the formula a = [(M1 - M2) / (M1 + M2)] * g. Substituting the given values: a = [(3 - 2) / (3 + 2)] * 10 = (1 / 5) * 10 = 2 m/s^2. The heavier mass accelerates downwards, the lighter one upwards.

This question belongs to: Science Physics