General Science Previous Year Questions (PYQ) with Answers – Page 72

Work done in moving a charge through a potential difference is W = Q × V, so W = 2 × 12 = 24 joule.

Borax, sodium tetraborate, is the salt of a strong base, sodium hydroxide, and a weak acid, boric acid, so its solution in water is basic.

Citrus fruits such as orange, lemon, lime and grapefruit owe their sharp sour taste to citric acid, which is the acid textbooks name for this family and the one examiners expect here.

Fat is digested in the small intestine by these two secretions working together.

Red algae, the division Rhodophyta, live in water, mostly in warm and shallow sea water, with a few species in fresh water.

Guava is the classic jam fruit because it is rich in both pectin and acid, the two things a jam needs to set into a firm gel.

Silk comes from the cocoon spun by the caterpillar of a moth. The common silk moth is Bombyx mori, and rearing it is called sericulture.

The ending 'al' marks an aldehyde, so propanal is the three-carbon aldehyde, CH3CH2CHO. An aldehyde carries the group -CHO at the end of the carbon chain, with the carbonyl carbon attached to a hydrogen.

A galvanometer detects whether a current is flowing in a circuit and shows its direction, because its needle moves to one side or the other about a central zero.

Electronegativity is the tendency of an atom to attract a shared pair of electrons towards itself. It increases from left to right across a period, as nuclear charge grows, and decreases down a group, as each new shell puts the outer electrons further from the nucleus.

The potential difference between two points in a circuit is defined as the work done in moving a unit positive charge from one point to the other.

By Ohm's law, at a constant temperature the current through a conductor is directly proportional to the potential difference across its ends, since the current equals the potential difference divided by the resistance.

Brakes work on friction: a lining is pressed against a moving drum or disc, and the rubbing force slows the wheel down.

Boron has three electrons in its outermost shell, so it is a trivalent element and is used as a p-type dopant.

A centre-tap full wave rectifier needs two p-n junction diodes, one for each half of the input cycle. The secondary winding of the transformer is tapped at its middle, so its two halves give equal voltages of opposite sign.

A silicon diode in forward bias drops about 0.7 volt across itself, whatever the supply voltage is.

Amplitude is the maximum displacement of a particle of the medium from its rest position, and the energy carried by a wave increases with the square of the amplitude.

Pitch is the characteristic of a sound by which the brain judges it as shrill or flat, and it is decided by the frequency of the wave.

The speed of a wave is the product of its frequency and its wavelength, so the speed here is 50 hertz multiplied by 4 metres, that is 200 metres per second.

By the sign convention the focal length of a concave lens is negative, so f is minus 15 centimetres, and the object distance measured against the direction of the incident light is minus 30 centimetres.