General Science Previous Year Questions (PYQ) with Answers – Page 39

Doubling one mass doubles the force, while doubling the distance cuts it to one-fourth, so the net result is 2 × 1/4 = 1/2.

By Coulomb's law the force F = kq₁q₂/r² comes out positive, meaning repulsive, whenever the two charges have the same sign.

Both changes let more molecules escape from the surface each second. Evaporation is a surface process: only molecules at the surface with enough energy break away into the air.

After 3 minutes 45 seconds the boy has completed seven and a half rounds, so he stands at the point exactly opposite his starting point.

In household wiring the wire with green insulation is the earth wire, not the live wire, so this statement is not correct.

Latent heat is absorbed during a change of state while the temperature stays fixed. When water boils at 100 °C, adding more heat does not raise its temperature; the energy goes into breaking the attractions between molecules so that liquid turns into vapour.

Using Q = mcΔT, the mass works out to 20,000 ÷ (400 × 10) = 5 kg. The heat needed to warm a body is Q = mcΔT, where m is the mass, c the specific heat capacity and ΔT the rise in temperature.

In a short circuit the live and neutral wires touch, the resistance of the path falls almost to zero, and the current shoots up.

Silver is the best conductor, nichrome is an alloy with high resistivity, and glass is an insulator with enormous resistivity.

A soap film is extremely thin, and light reflected from its front surface meets light reflected from its back surface.

Milk is an emulsion because it is tiny drops of liquid fat spread through water, and an emulsion is a colloid in which one liquid is dispersed in another liquid.

A suspension is a heterogeneous mixture because the particles of the solute are large enough to be seen, they do not dissolve, they settle when the mixture is left standing and they can be separated by filtering.

Coulomb’s law gives the force between two point charges at rest. It states that the force is directly proportional to the product of the two charges and inversely proportional to the square of the distance between them, and acts along the line joining them.

The petiole is the stalk that joins a leaf blade to the stem; it belongs to the leaf, not to the flower, and a leaf without one is called sessile.

A bacterial flagellum is built of exactly these three parts. The filament is the long thread outside the cell, made of the protein flagellin coiled into a hollow helix, and it acts like a propeller.

Reduction means the loss of oxygen or the gain of hydrogen, so each statement states one half of the same definition.

Rust of wheat is indeed a fungal disease, caused by species of Puccinia, and it is named from the reddish brown spores that appear in streaks on the leaves and stem.

In a thermoplastic the polymer exists as long linear or lightly branched chains, and one chain is held to the next only by weak secondary forces such as van der Waals attraction.

Flatworms, the phylum Platyhelminthes, have an incomplete digestive system with just one opening, so the same mouth takes the food in and throws the waste out.

Group 15, the nitrogen family, holds nitrogen, phosphorus, arsenic, antimony and bismuth. Only nitrogen and phosphorus are non-metals; arsenic and antimony are metalloids and bismuth is a metal, so the group has exactly two non-metallic elements.