General Science GK Questions with Answers – Page 117

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.

A denser medium has a higher refractive index, and the refractive index is the speed of light in vacuum divided by its speed in the medium, so light must travel more slowly inside it.

Pneumonia is an infection of the lungs in which the alveoli, the tiny air sacs where oxygen passes into the blood, fill with fluid or pus.

Among the four, the ant has the largest brain in proportion to its body. An ant’s brain is tiny in absolute terms, with about two hundred and fifty thousand neurons, yet it makes up roughly a sixth of the insect’s body weight, a share no vertebrate comes close to.

Distillation separates a liquid from a solution or from another liquid by boiling it and condensing the vapour, so it is used when the components differ in boiling point, as in getting pure water from salt water or separating acetone from water.

Among the allotropes of carbon, graphite has the lowest standard enthalpy of formation, which is taken as zero, so it is the reference state and the most stable form under ordinary conditions of temperature and pressure.

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.

A conservative force is one whose work depends only on the starting and the finishing point, not on the path taken, and whose work around any closed path is zero.

Opium is the dried latex of the opium poppy, whose botanical name is Papaver somniferum; the second word means sleep bringing.

The BCG vaccine takes its name from Albert Calmette and Camille Guerin, the two French scientists who developed it from a weakened strain of Mycobacterium bovis.

CH3CH2OH, also written C2H5OH, is ethanol or ethyl alcohol, the second member of the alcohol family. The -OH group attached to the carbon chain is the functional group that makes it an alcohol.

Pressure is the force acting on unit area, that is P equals F divided by A, so for the same force a larger area of contact means smaller pressure.

Atmospheric pressure at sea level is about 1.013 into 10 to the power 5 pascal, which presses with roughly the weight of one kilogram on every square centimetre of our body, so it is very large and not negligible at all.

Sulphur dioxide dissolves in water to give sulphurous acid, a weak acid with the formula H2SO3, by the reaction SO2 + H2O to H2SO3.

A magnet cannot be cut into a single north pole and a single south pole.

Loudness and frequency are two different properties of sound. Loudness depends on the amplitude of the vibration, that is how far the vibrating part moves from its rest position, while frequency is the number of vibrations made in one second and is measured in hertz.

A floating body is at rest, so the upward buoyant force must exactly balance the downward weight of the object.

Algae belong to Thallophyta, the simplest division of the plant kingdom. Their body is a thallus, which means it is not divided into root, stem and leaf, and they have no vascular tissue.

An iron rod is a solid, and the force of attraction between particles is strongest in the solid state. In a solid the particles sit close together in fixed positions and can only vibrate, so a solid keeps its shape, has a definite volume and can hardly be compressed.

The work done against gravity is mgh = 40 × 10 × 5 = 2000 joule, and power is work divided by time, so 2000 ÷ 4 = 500 watt.