Physics Questions and Answers

Answer: C

Glass wool is the best sound absorber here.

It is a porous, fibrous mat full of trapped air. Sound entering it sets the air and fibres vibrating, and the viscous friction converts the energy to heat. Stone, steel and glass are dense and rigid, so they reflect sound rather than absorbing it.

Answer: C

The length of the day is determined in astronomical units of measurement.

A solar day is defined by the earth's rotation relative to the sun - the interval between successive passages of the sun across the meridian - and is measured by astronomical observation. The sidereal day, measured against the fixed stars, is about four minutes shorter.

Answer: D

Neutrons are not emitted in ordinary radioactive decay.

Radioactive substances emit alpha particles, beta particles (electrons) and gamma rays (electromagnetic radiation). Free neutrons come from fission and from certain induced reactions, not from spontaneous decay.

Answer: D

National Science Day is celebrated on 28 February.

It marks the day in 1928 on which C.V. Raman discovered the effect that bears him name, work for which he received the Nobel Prize in Physics in 1930. The day has been observed since 1987.

Answer: B

To reduce the friction between the wheel and the axle.

The balls turn the sliding contact of the axle in its housing into a rolling one, and rolling friction is smaller by a factor of a hundred or more. The point of contact is momentarily at rest, so the surfaces do not scrape.

Answer: A

The reaction is greater than the weight of the man.

The floor must support him and accelerate him upward as well: \[N - mg = ma \Rightarrow N = m(g+a)\] This is why one feels heavier as a lift starts up, and lighter as it starts down.

Answer: A

Argon, copper and silver are diamagnetic.

A diamagnetic substance has all its electrons paired, so it has no permanent magnetic moment and is weakly repelled by a field. Oxygen has two unpaired electrons and is paramagnetic, and hydrogen atoms are paramagnetic though \(\mathrm{H_2}\) is not.

Answer: C

The total weight remains the same.

The balance reads the total weight of everything the man and his load contain. Moving the fish from one hand to the other, or into the bucket, moves mass about within that system but adds and removes nothing, so the reading does not change.

Answer: B

Because the forces of cohesion between the molecules are very large.

In a solid the intermolecular forces hold each molecule near a fixed lattice site, so it can only vibrate about that point. In liquids these forces are weaker and molecules can slide past one another, so a liquid takes the shape of its container.

Answer: A

Because the harmonium uses a tempered scale.

Its reeds are tuned to fixed, equally spaced semitones, so the intervals are slight compromises. Indian classical music uses just intonation with microtonal shrutis and continuous glides between notes - neither of which a fixed-pitch reed instrument can follow, which is why the sarangi and now the violin are preferred.