Physics Questions and Answers

Answer: B

The distance is \(\lambda/4\).

In a standing wave, consecutive nodes are half a wavelength apart, and an antinode sits exactly midway between two nodes. The node-to-antinode distance is therefore half of that, \(\lambda/4\).

Answer: A

The time of ascent is less than the time of descent.

Air resistance always opposes motion. Going up it acts downwards, so the retardation is \(g + a\) and the ball slows faster; coming down it acts upwards, so the acceleration is only \(g - a\). The larger effective acceleration on the way up means less time is spent there.

Answer: D

Fat separates because of the centrifugal effect.

In the rotating drum, the denser skimmed milk is thrown to the outside and the lighter fat globules are displaced inwards, so the cream collects near the axis. In the rotating frame this is described as a centrifugal force; in the ground frame it is the denser fluid's greater inertia.

Answer: C

The maxwell is the unit of magnetic flux.

It is the CGS unit: one maxwell is one line of flux, and \(1\ \mathrm{Wb} = 10^{8}\ \mathrm{Mx}\). The SI unit is the weber.

Answer: C

Escape velocity is the minimum velocity with which a body must be projected to escape the earth's gravitational field.

Equating kinetic energy to the depth of the gravitational well: \[\tfrac{1}{2}mv^2 = \frac{GMm}{R} \Rightarrow v = \sqrt{2gR} = 11.2\ \mathrm{km\,s^{-1}}\] It does not depend on the mass of the escaping body, nor on the direction of projection.

Answer: D

This is the elastic limit.

Up to it the body returns exactly to its original shape when the load is removed; beyond it a permanent set remains. It should not be confused with the breaking stress, which lies further along the stress-strain curve.

Answer: B

This is the greenhouse effect.

Short-wavelength sunlight passes through the glass and is absorbed by the seats and dashboard, which then re-radiate at much longer infrared wavelengths. Glass is opaque to that infrared, so the heat is trapped, and the closed windows also prevent it escaping by convection.

Answer: B

Electrical pressure is another name for voltage.

The analogy is with a water circuit: voltage is the pressure that drives the flow, current the rate of flow, and resistance the constriction opposing it. The relation is Ohm's law, \(V = IR\).

Answer: D

Oil is the most viscous of these.

Viscosity measures resistance to flow, and it rises with the size of the molecules and the strength of the forces between them. Lubricating oil has long hydrocarbon chains that tangle, while water and milk flow freely.

Answer: C

Displacement is the shortest distance covered in a definite direction.

It is the straight-line vector from start to finish, so it has both magnitude and direction, and can be zero even after a long journey if the body returns to where it began. Distance is the scalar length of the actual path and can only increase.