Physics Questions and Answers

Answer: D

RADAR is used for detecting and locating objects such as aircraft.

The name is short for Radio Detection and Ranging. A pulse of radio waves is sent out and the echo timed; the range follows from \(d = ct/2\), and the direction from where the antenna was pointing. Radio waves do not penetrate sea water, so submerged submarines are found by sonar instead.

Answer: A

The volume of the cavity will increase.

On heating, every linear dimension of the solid grows by the same factor, and the cavity scales with the rest - it expands exactly as if it were filled with the same metal. This is why a hole in a heated plate gets bigger, not smaller.

Answer: A

The primary colours of light are red, green and blue.

They match the three types of cone in the retina, and mixing them additively in the right proportions produces any colour, including white. Pigments mix subtractively, and their primaries are cyan, magenta and yellow.

Answer: B

Impulse is the vector quantity.

It is force multiplied by time, and force has direction, so impulse does too - it equals the change in momentum. Pressure, gravitational potential and the coefficient of friction are all scalars.

Answer: A

Because steam carries latent heat.

Steam and boiling water are both at 100 °C, but steam must give up its latent heat of vaporisation - about \(2260\ \mathrm{kJ\,kg^{-1}}\) - as it condenses on the skin, before it even begins to cool. That extra heat is what makes the burn so much worse.

Answer: C

Soda is a heterogeneous mixture.

Carbonated water holds undissolved carbon dioxide as visible bubbles, so it has two distinct phases and its composition is not uniform throughout. Air and brass are homogeneous mixtures, and table salt is a compound rather than a mixture at all.

Answer: B

The electron moves towards B.

Conventional current and positive charge move from high to low potential; an electron, being negative, is attracted the other way, towards the higher potential. B is at the higher potential, so the electron accelerates towards it.

Answer: C

The ozone layer protects us from ultraviolet rays.

Ozone absorbs strongly between about 200 and 320 nm, screening out almost all UV-C and most UV-B - the wavelengths that damage DNA and cause skin cancer and cataract. Visible light and infrared pass through freely.

Answer: B

This is the Doppler effect.

The observed frequency shifts because successive wavefronts have less distance to travel when source and observer approach: \[f' = f\left(\frac{v \pm v_o}{v \mp v_s}\right)\] It explains the falling pitch of a passing horn and the redshift of receding galaxies.

Answer: C

No current flows if the two bodies are at the same potential.

Charge flows in response to a potential difference, not to a difference in charge. A large body may hold much more charge than a small one and still sit at the same potential, since \(V = Q/C\).