Physics Questions and Answers

Answer: D

Stock value is not a term in physics.

It belongs to finance. Latent heat is the energy absorbed in a change of state, nuclear fusion the joining of light nuclei, and refractive index the ratio \(c/v\) for a medium.

Answer: A

Because metals contain free electrons.

In the metallic bond, the valence electrons are delocalised over the whole lattice rather than bound to individual atoms. An applied field sets this electron sea drifting, which is the current. The same electrons also carry heat, which is why good electrical conductors are good thermal ones.

Answer: A

A parsec is a unit of distance.

It is the distance at which one astronomical unit subtends an angle of one arcsecond - the name is short for parallax-second. One parsec is about \(3.26\) light years, or \(3.086\times10^{16}\) m.

Answer: C

The IC chip is made of silicon.

Silicon is a semiconductor whose conductivity can be controlled precisely by doping, it is abundant as sand, and it forms a stable insulating oxide, \(\mathrm{SiO_2}\), that makes the layered fabrication of integrated circuits possible.

Answer: B

This is due to interference.

Light reflected from the top of the oil film and light reflected from the oil-water boundary travel different distances and interfere. The path difference depends on the film's thickness and on the wavelength, so different colours reinforce at different thicknesses, giving the shifting bands.

Answer: C

An electric motor converts electrical energy into mechanical energy.

A current-carrying coil in a magnetic field experiences a force \(F = BIL\), and the resulting couple turns the armature. A generator is the same machine run backwards, converting mechanical energy into electrical.

Answer: A

Fog is a liquid dispersed in a gas.

It is an aerosol of tiny water droplets suspended in air, formed when moist air is cooled below its dew point. Smoke is a solid in a gas, an emulsion a liquid in a liquid, and foam a gas in a liquid.

Answer: B

Such stars are binaries.

A binary is a pair of stars bound by gravity and orbiting their common centre of mass, too close together to be separated by the eye but resolved in a telescope. More than half the stars in the sky are thought to belong to multiple systems.

Answer: A

A telescope has an objective of large focal length and an eyepiece of small focal length.

Its magnification is \(f_o/f_e\), so a long objective focal length helps. A microscope is the other way round: its objective has a very short focal length, of a few millimetres, to give a large magnified real image which the eyepiece then magnifies again.

Answer: C

Lightning conductors are made of copper.

Copper conducts almost as well as silver at far less cost, so it carries the enormous discharge current to earth without melting, and it resists corrosion out of doors. The conductor runs from a pointed rod above the roof to a plate buried in moist earth.