Physics Questions and Answers

Answer: B

The filament is made of Tungsten.

An incandescent bulb gives light by heating its filament to well over 2,000 °C. Tungsten has the highest melting point of all metals, about 3,422 °C, and a low rate of evaporation, so it can glow white-hot for hundreds of hours.

Copper and lead melt at about 1,085 °C and 327 °C, far too low. Silicone is a rubbery polymer, not a metal, and would burn.

Answer: C

A TV remote uses Infrared waves (printed 'Infared').

The remote has an infrared LED that sends coded pulses of light just beyond the red end of the visible spectrum, and a sensor on the television decodes them. That is why the remote must point at the set with nothing in the way.

Radio waves and microwaves are used by Wi-Fi, Bluetooth and some newer remotes, not the common infrared type. Ultrasonic remotes, which signalled with sound, appeared in some early sets but are not the common kind.

Answer: C

The quantity measured in kg m/s² is force.

By Newton's second law, force = mass × acceleration. Mass is in kilograms and acceleration in metres per second squared, so force is in kg m/s², the unit called the newton.

Work (energy) is in kg m²/s², the joule, and power in kg m²/s³, the watt. 'Motion' is not a physical quantity with a unit.

One newton is the force that gives a mass of 1 kg an acceleration of 1 m/s².

Answer: B

The boiling point inside a pressure cooker is about 121°C.

The boiling point of water rises with pressure. A sealed pressure cooker traps steam until the pressure inside is about twice atmospheric pressure (roughly 15 psi above it), at which water boils at about 121°C. The higher temperature cooks food faster.

100°C is the boiling point at normal atmospheric pressure, 95°C is what it falls to at high altitude, and 0°C is the freezing point.

Answer: A

The magnification is less than the object: the image is smaller.

Rear view mirrors are convex mirrors. A convex mirror always forms a virtual, erect and diminished image, whatever the position of the object, so its magnification is always less than one. In return it gives the driver a much wider field of view.

An image larger than the object, or one that can be larger or smaller depending on where the object is, is the behaviour of a concave mirror. A plane mirror would give an image equal in size.

Answer: C

The best choice is a convex lens of focal length 5 cm.

A magnifying glass is a convex lens with the object placed within its focal length, giving an enlarged, erect, virtual image. Its magnification is about \(1 + \frac{D}{f}\), with \(D = 25\) cm, so a shorter focal length magnifies more:

\[ \begin{aligned} f = 5\ \text{cm} &: \ 1 + \frac{25}{5} = 6 \\ f = 50\ \text{cm} &: \ 1 + \frac{25}{50} = 1.5 \end{aligned} \]

Concave lenses always form smaller images, so neither concave option can magnify small print.

Answer: A

The force is the force of gravitation.

Water in a river flows downhill from higher to lower ground because gravity pulls it towards the Earth's centre. The steeper the slope of the river bed, the faster it flows.

Friction with the river bed and banks opposes the flow rather than driving it, and electrostatic and magnetic forces play no part in it.

It is the component of gravity along the sloping river bed that carries water from the river's source in the hills down to the sea.

Answer: C

A rocket works on Newton's third law.

The third law says that for every action there is an equal and opposite reaction. A rocket burns fuel and forces hot exhaust gases out backwards at high speed; the gases push back on the rocket with an equal and opposite force, which drives it forward. Because it needs nothing to push against, a rocket works even in the vacuum of space.

The first law (inertia) and the second law (force equals rate of change of momentum) describe how the rocket's motion changes once the force acts, but the principle that produces the thrust is the third law, which is why the answer is the third law rather than 'All of the above'.

Answer: D

A fuse wire has high resistance and low melting point.

A fuse protects a circuit by melting when too much current flows. Its high resistance makes it heat up quickly as the current rises (heat produced is \(I^{2}R\)), and its low melting point makes it melt at that temperature before the other wiring is damaged. Fuse wire is traditionally an alloy of tin and lead.

A wire with high melting point would not melt in time, and a low-resistance wire would not heat up enough, so every other combination defeats the purpose of the fuse.

Answer: B

J. J. Thomson won the Nobel Prize for the discovery of Electrons.

J. J. Thomson identified the electron in 1897 through his experiments with cathode rays, showing they were made of tiny negatively charged particles. He received the Nobel Prize in Physics in 1906 for his work on the conduction of electricity by gases.

The proton is credited to Ernest Rutherford, the neutron was discovered by James Chadwick (Nobel 1935), and the positron by Carl Anderson (Nobel 1936).