General Science Previous Year Questions (PYQ) with Answers – Page 65

Light inside an optical fibre strikes the wall at more than the critical angle, is totally reflected back inside, and repeats this again and again along the fibre.

Nitrogen and oxygen combine only when a lot of energy is supplied. The nitrogen molecule is held by a very strong triple bond, so breaking it takes much energy, and the reaction N₂ + O₂ → 2NO absorbs heat.

It is a carbon compound with a carboxyl group, so it is an organic acid. Acetic acid (ethanoic acid, CH₃COOH) contains the –COOH group typical of carboxylic acids.

The reaction happens because iron is more reactive than copper and pushes it out of its salt, so statement C is false.

These four elements make up the complex tissue that carries water and minerals upward from the roots. Tracheids and vessels are long, dead, thick-walled tubes through which water moves; xylem parenchyma is the only living part and stores food; xylem fibres give support.

A nuclear reactor splits heavy nuclei such as uranium-235 in a chain reaction that is kept under control, releasing heat at a steady rate.

Mitochondria have their own DNA and their own ribosomes, so they can make some of the proteins they need. Mitochondria are the "powerhouses of the cell", where food is broken down in aerobic respiration to release energy stored as ATP.

Pure iron melts at about 1,538°C, so 1,500°C is the only option close to its melting point. Iron is a metal with strong metallic bonds, so a great deal of heat is needed to break up its solid structure.

Blood is a fluid connective tissue, with cells floating in a liquid matrix called plasma. Connective tissues link and support other parts of the body, and they have cells spread out in a matrix.

Sound travels through water at about 1,480 metres per second at 20°C, which rounds to 1,500 m/s. Sound is a mechanical wave and needs a medium.

Osmosis is the movement of water from a dilute solution to a more concentrated one across a selectively permeable membrane.

Velocity ratio is defined as the distance moved by the effort divided by the distance moved by the load in the same interval of time, and because it depends only on the design of the machine it does not change with friction, unlike the mechanical advantage.

The velocity ratio is the distance moved by the effort divided by the distance moved by the load, that is ten divided by two point five, which is four.

Mechanical advantage is defined as the load divided by the effort, so the load is the mechanical advantage multiplied by the effort, that is three multiplied by fifteen, which gives forty-five units.

An insulator is charged by friction: rubbing transfers electrons from one surface to another, and because electrons cannot move through an insulator, the charge stays where it is as static electricity.

Tin is a chemical element (symbol Sn, atomic number 50), a pure substance made of only one kind of atom, so it is not a mixture.

In 5 seconds the sound travels to the mountain and back, a total of 340 × 5 = 1,700 m, so the mountain is half of that, 850 m or 0.85 km, away.

In uniform circular motion the speed stays the same, but the direction of the velocity keeps changing, so the car is always accelerating and the direction of that acceleration keeps changing too.

Soap lowers the surface tension of water, so water spreads into fine gaps and wets greasy dirt that plain water would bead up on.

Lime water is a solution of calcium hydroxide, Ca(OH) 2, not calcium carbonate.