General Science Previous Year Questions (PYQ) with Answers – Page 23

It gives the direction of the force, and so of the motion, on a current-carrying conductor placed in a magnetic field, which is exactly what turns the coil of a motor.

Combustion means burning in oxygen, and complete burning of methane gives carbon dioxide, water, heat and light. The equation is balanced: one carbon, four hydrogen and four oxygen atoms on each side.

At great heights the air is thin, so the atmospheric pressure acting on the body is much lower than at sea level.

All three are needed by plants only in very small amounts, which makes them micronutrients. Plants need macronutrients in large amounts: nitrogen, phosphorus and potassium as primary nutrients, and calcium, magnesium and sulphur as secondary ones.

Of the three, only citrus canker is caused by bacteria; rust of wheat is caused by a fungus and yellow vein mosaic of bhindi by a virus.

Veins usually carry blood low in oxygen back to the heart, but the pulmonary veins are the exception. After blood picks up oxygen in the lungs, four pulmonary veins, two from each lung, bring this oxygen-rich blood to the left atrium of the heart.

One ampere is the current that flows when one coulomb of charge passes a point in a circuit in one second.

Mature red blood cells, or erythrocytes, lose their nucleus before they enter the blood. Losing the nucleus, and the mitochondria too, leaves more room for haemoglobin, the iron-rich protein that carries oxygen, and gives the cell its flexible biconcave disc shape, which lets it squeeze through narrow capillaries.

It is the main growth inhibitor among plant hormones and works against the growth promoters.

Each human kidney has about one million nephrons, and every nephron begins with a cup-shaped Bowman's capsule that encloses a knot of capillaries called the glomerulus.

Vitamin D helps the intestine absorb calcium and phosphorus, so without it the bones of a growing child stay soft and bend, giving bow legs, a pigeon chest and a large forehead; this disease is rickets.

LIGO, the Laser Interferometer Gravitational-Wave Observatory in the USA, detected gravitational waves for the first time in September 2015 (announced in February 2016), and such waves were predicted by Einstein's general theory of relativity in 1916.

Milk of magnesia is a white suspension of magnesium hydroxide, Mg(OH)2, in water, and its milky look gives it the name.

Laughing gas is nitrous oxide, N2O, a colourless gas with a faintly sweet smell that makes people giggle and feel light-headed when they breathe it in.

The name itself gives the formula: 'hexa' means six, so sulphur hexafluoride has one sulphur atom joined to six fluorine atoms, SF6.

In a given medium under the same conditions, sounds of all frequencies travel at the same speed; the speed depends on the medium, not on the pitch.

In glass, light of shorter wavelength travels more slowly, so the glass has a higher refractive index for it and bends it more.

The bulb's resistance stays the same, and since power varies as the square of voltage, halving the voltage cuts the power to one-fourth.

This follows from Newton's third law and his law of gravitation. Newton's law of gravitation gives the force between two bodies as F = Gm₁m₂/r².

Sound needs a material medium to travel, and in air its particles vibrate back and forth along the direction the wave moves.