Physics Questions and Answers

Answer: D

A ball pen works on capillarity and surface tension.

Ink is drawn along the narrow tube by capillary action and held at the tip by surface tension, so it does not run out. Rolling the ball picks up a film of ink and lays it on the paper.

Answer: B

An optical fibre works by total internal reflection.

The core has a slightly higher refractive index than the cladding, so light striking the boundary beyond the critical angle is reflected entirely back into the core, and travels the length of the fibre in a zigzag with almost no loss.

Answer: A

The SI unit of temperature is the kelvin.

It is one of the seven base units, and the scale starts at absolute zero, so no negative values occur. A kelvin and a degree Celsius are the same size, and \(T(\mathrm{K}) = t(^\circ\mathrm{C}) + 273.15\).

Answer: C

The temperature decreases slightly.

Evaporation removes the fastest molecules from the surface, lowering the average kinetic energy of those left behind, and the latent heat of vaporisation is drawn from the water itself. The drop is small because heat flows in from the surroundings to replace it.

Answer: C

It will bend towards the left, that is towards the iron.

Copper's coefficient of linear expansion is about \(17\times10^{-6}\ \mathrm{K^{-1}}\) against iron's \(12\times10^{-6}\). On heating, the copper strip lengthens more, and since the two are welded the strip must curve with copper on the outside - so the free end swings towards the iron side.

Answer: C

Heat flows according to the temperatures of the two objects.

It always passes from the hotter to the colder body, whatever their masses or heat contents, until both reach the same temperature. This is the content of the second law of thermodynamics, and the reason the zeroth law makes temperature meaningful.

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.