General Science Previous Year Questions (PYQ) with Answers – Page 74

Brewster found that when unpolarised light falls on a transparent surface at one particular angle of incidence, called the polarising angle, the reflected light is completely plane polarised, and at that angle the refractive index of the surface equals the tangent of the polarising angle.

Colostrum is the thick, yellowish first milk a mother produces in the first few days after childbirth.

A swing is a pendulum, and its speed is greatest at the lowest point, where all the potential energy gained at the top has turned into kinetic energy.

These ducts and glands do not make sperm; they help sperm mature, store and move them, and add the fluid in which sperm swim.

The eyes of a potato are nodes with buds, and only a stem bears nodes and buds, so they prove that the potato is a modified stem.

Rubidium, an alkali metal like caesium, gives off electrons easily when light falls on it, so it is used in photoelectric cells.

An alloy of sodium and potassium, called NaK, stays liquid at room temperature and carries heat away from the core of some nuclear reactors.

Near the horizon, sunlight crosses a much thicker layer of air, and scattering removes most of the blue light before it reaches us.

The glass of a glowing bulb is heated mainly by radiation from the white-hot filament, not by convection. Conduction passes heat through a solid from particle to particle, convection carries heat by the actual movement of a fluid, and radiation sends heat as electromagnetic waves that need no medium.

Caesium melts at about 28.5 °C, the lowest of these alkali metals, so it can turn liquid on a warm day or in the hand.

Powers of lenses in contact simply add, so the combination has a power of 2 + 2 = 4 dioptre, and its focal length is 1/4 m, that is 0.25 m. The power of a lens is the reciprocal of its focal length in metres, P = 1/f, and is…

It states that when hot and cold bodies are mixed in an insulated system, heat lost by the hot body equals heat gained by the cold body.

Superphosphate of lime is made by treating rock phosphate with sulphuric acid, and the nutrient it supplies is phosphorus in the form of available phosphate, not nitrogen; it is therefore a phosphatic fertiliser.

Light travels fastest in vacuum and almost as fast in air, so in any material medium it moves more slowly than in air, and the ratio of the two speeds is greater than one.

Power is the reciprocal of focal length in metres, and 50 cm is 0.5 m, so the power is 1 divided by 0.5, which is +2 dioptre.

Isobars are atoms of different elements with the same mass number, and 18 + 22 gives a mass number of 40, the same as calcium.

A direction in space needs two angles, one in the horizontal plane and one in the vertical plane, and declination and inclination supply exactly these.

For a swinging pendulum, the component of the bob's weight along its path always pulls it back towards the lowest point, so gravity acts as a restoring force.

Specific heat is a property of the material, not of the size or shape of the particular body. It is the amount of heat needed to raise the temperature of unit mass (1 kg or 1 g) of a substance by one degree.

X-rays have wavelengths of roughly 0.01 to 10 nanometres, and a typical value is about one ångström (1 Å = 10⁻¹⁰ m = 0.1 nm).