General Science Questions and Answers

Answer: B

Transistors are made from silicon and germanium.

Both are group 14 semiconductors, whose conductivity can be controlled precisely by doping with traces of boron or phosphorus. Germanium was used in the first transistors; silicon replaced it because it withstands higher temperatures and forms a stable oxide.

Answer: B

Deliquescence is the property of absorbing so much moisture from the air that the substance dissolves in it, forming a solution.

Calcium chloride and sodium hydroxide are deliquescent. The opposite is efflorescence, where a hydrated crystal loses its water to the air and crumbles to powder.

Answer: A

Tides are caused chiefly by the gravitational attraction of the moon, with the sun contributing about half as much.

The moon pulls the water nearest it into a bulge, and the water on the far side is left behind in a second bulge, so most coasts have two high tides a day.

Answer: B

Hydrogen is not a noble gas. It sits in group 1 of the periodic table and is highly reactive, burning in air and combining with most elements.

Helium, neon, argon, krypton, xenon and radon make up group 18, the noble gases, whose full outer shells make them almost entirely unreactive.

Answer: B

Glass is made from sand and silicates - silica fused with sodium carbonate and limestone.

The soda lowers silica's melting point from about 1,700°C to a workable temperature, and the lime stops the product dissolving in water. The mixture cools to a rigid but non-crystalline solid.

Answer: C

Micro-organisms can be seen only with a microscope. The unaided eye resolves objects down to about 0.1 mm, and most bacteria are between 0.5 and 5 micrometres - a hundred times smaller.

A hand lens magnifies only about ten times, which is far short of what is needed.

Answer: B

A dynamo converts mechanical energy into electrical energy. A coil rotated in a magnetic field has a current induced in it, by Faraday's law of electromagnetic induction.

The reverse device, converting electrical energy into mechanical, is the electric motor.

Answer: C

A cream separator works by centrifugal force. Spinning the milk at high speed throws the denser skim milk to the outside of the bowl while the lighter fat globules collect nearer the axis, and the two are drawn off separately.

Gravity separates cream too, but far more slowly - the centrifuge does in seconds what standing does in hours.

Answer: D

Pluto takes about 248 Earth years to orbit the sun once.

Its orbit is highly elliptical, carrying it from 30 to 49 astronomical units from the sun, and it is tilted 17° to the plane of the planets. It has not completed a single orbit since its discovery in 1930.

Answer: B

The Mid Day Meal scheme is the one aimed at school-going children, providing a cooked meal in government and aided schools.

Launched nationally in 1995, it is the largest school feeding programme in the world, and was intended to improve both nutrition and school attendance.