General Science Previous Year Questions (PYQ) with Answers – Page 80

Constant velocity means both the speed and the direction stay the same, so the speed cannot change. Velocity is a vector: it has a magnitude, the speed, and a direction.

The balanced equation is Fe2O3 + 3CO → 2Fe + 3CO2, which has equal numbers of every atom on both sides.

For small swings the time period is T = 2π√(L/g), which contains the length and gravity but neither the mass nor the amplitude.

Moving a substance from low to high concentration is uphill work, and the cell pays for it with ATP.

The RER is studded with ribosomes, the actual sites where amino acids are joined into proteins. Ribosomes read the message carried by mRNA and link amino acids in the right order.

This is the incorrect statement, because periodic motion repeats after every interval T, again and again. The time period T of a pendulum is the time for one complete oscillation, that is, the smallest interval after which the bob returns to the same position moving in the same direction.

These are the three places in a eukaryotic cell where DNA is found. The nucleus holds nearly all of a cell's DNA, packed with proteins into chromosomes.

Heat, by definition, is energy that flows because of a temperature difference. Thermodynamics recognises two ways in which a system can exchange energy with its surroundings: heat and work.

A magnesium atom sits at the centre of every chlorophyll molecule, so a plant cannot make chlorophyll without it. Chlorophyll is built around a ring-shaped structure called a porphyrin, with a single magnesium ion held at its centre.

A carbonate reacts with an acid at room temperature to give carbon dioxide, and only carbon dioxide turns limewater milky.

For a 4d orbital, n = 4 and l = 2, which gives l = 2 angular nodes and n − l − 1 = 1 radial node.

A liquid boils when its vapour pressure equals the pressure above it, so less outside pressure means boiling starts at a lower temperature.

A compound microscope uses two convex lenses, and its magnification depends on the tube length. The objective is a convex lens of very short focal length that forms a real, enlarged image of the specimen.

Light inside the fibre strikes the boundary at more than the critical angle, so it is reflected back again and again instead of escaping.

All three are adaptations of desert plants (xerophytes) that cut down water loss through transpiration. Plants lose most of their water through the leaves, so desert plants change their leaves to save it.

By Archimedes' principle the upthrust on a body equals the weight of the fluid it displaces, and that weight is the volume of the body actually immersed multiplied by the density of the fluid and by the acceleration due to gravity.

A change of state is governed by the energy of the particles. When a solid absorbs heat its particles vibrate harder until the force holding them in the lattice is overcome and it melts; further heat lets the liquid particles escape as vapour.

In 1932 Chadwick bombarded beryllium with alpha particles and showed that the highly penetrating radiation given off consisted of neutral particles with almost the same mass as a proton.

In 1897 Thomson passed an electric discharge through a gas at very low pressure and showed that the cathode rays produced were a stream of identical negatively charged particles, far lighter than any atom and the same whatever gas or electrode was used.

Bakelite is a thermosetting polymer, made by condensing phenol with formaldehyde, and once it has set under heat its chains are cross-linked, so it cannot be melted and moulded again.