999+ Physics Questions Answers Explanation MCQ

Q:

A piece of ice is floating in water kept in a beaker. When all the ice melts the level of water will

A) first rise and then fall	B) fall
C) remain the same	D) rise

Answer & Explanation Answer: C) remain the same

Explanation:

The submerged portion of the ice on melting shrinks a little in volume. so the level of water goes down a little.But this is just made up by the water added by the melting of upper portion. Addition is equal to the Shrinkage. Hence level is unchanged.

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Q:

A disk and a sphere of same radius but different masses roll on two inclined planes of the same altitude and length. Which one of the two objects gets to the bottom of the plane first ?

A) Depends on their masses	B) Sphere
C) Disk	D) Both reach at the same time

Answer & Explanation Answer: B) Sphere

Explanation:

Time does not depend on mass, else

$T \infty \sqrt{(1 + \frac{k^{2}}{R^{2}})}$

$\frac{k^{2}}{R^{2}}$ => is least for 'sphere' and

hence least time is taken by sphere.

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Q:

Two metallic plate of equal thickness and coefficient thermal conductivity K1 and K2 put together face to face. A common plate is constructed. What is equivalent K?

A) K1k2/k1+k2	B) 2k1k2/k1+k2
C) K1+k2/k1k2	D) None

Answer & Explanation Answer: B) 2k1k2/k1+k2

Explanation:

We know that,

The equivalent K = $\frac{L 1 + L 2}{\frac{L 1}{K 1} + \frac{L 2}{K 2}}$

where L1 & L2 are plate1 & Plate2 thicknesses, K1 & K2 are coefficient thermal conductivity of plate1 & Plate2 respectively.

But here L1 = L2 = L (say)

Then K = L+L/(L/K1 + L/K2) = $\frac{2 K 1 K 2}{K 1 + K 2}$

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Q:

Decibel is the unit of

A) speed of light	B) intensity of sound
C) intensity of heat	D) None of these

Answer & Explanation Answer: B) intensity of sound

Explanation:

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Q:

An object at rest may have

A) Momentum	B) Potential energy
C) Velocity	D) Kinetic energy

Answer & Explanation Answer: B) Potential energy

Explanation:

An object at rest may have Potential energy.

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Q:

Which of the following has the highest entropy?

A) Hydrogen	B) Diamond
C) Liquid nitrogen	D) Mercury

Answer & Explanation Answer: A) Hydrogen

Explanation:

Entropy is a measure of disorder . It will be maximum in gases followed by liquids and least in solids.

Hence, here the gas is only hydrogen and it has the highest entropy.

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Q:

Sound becomes hazardous noise pollution at decibels?

A) above 120 db	B) above 80 db
C) above 50 db	D) above 30 db

Answer & Explanation Answer: A) above 120 db

Explanation:

Sound intensity is measured in decibels(db). Sound pollution above 120 db becomes more hazardous and have adverse affects on human life.

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Q:

Quality of transmission depends upon

A) Nature of signal only	B) Nature of medium only
C) Both (A) and (B)	D) Neither A nor B

Answer & Explanation Answer: C) Both (A) and (B)

Explanation:

Quality of transmission is governed both by nature of signal and nature of communication channel/medium.

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