General Science Mixed Quiz: Set 197

Linear momentum stays constant only when no net external force acts. Linear momentum is the product of mass and velocity, p = mv.

Neither beta nor gamma emission changes the total number of protons and neutrons in a nucleus, so the mass number stays the same.

. For a stone whirled in a circle, the string pulls it towards the centre, while the stone moves along the circle, tangent to it at every instant.

An LED is a semiconductor p–n junction diode that gives out light when current flows through it in the forward direction.

Gravitational force varies inversely with the square of the distance, so doubling the distance cuts the force to one-fourth.

Galvanisation is the coating of iron or steel with zinc, usually by dipping it in molten zinc.

A plane mirror is a spherical mirror of infinite radius of curvature, so its focal length f = R/2 is also infinite.

Destructive distillation means heating coal strongly in the absence of air, so that it decomposes instead of burning. The solid left behind is coke, which is almost pure carbon and is used as a reducing agent in the extraction of iron and other metals and as a smokeless fuel.

Reverberation is the persistence of sound in a hall after the source has stopped, caused by repeated reflections from the walls, ceiling and floor.

Bisphenol A is the main building block from which polycarbonate plastic is made. Polycarbonate is a hard, clear and shatter-resistant plastic once widely used for reusable water bottles, baby feeding bottles, food containers, CDs and spectacle lenses.

Resistivity is a property of the material and its temperature, not of the wire's shape, so every copper wire has the same resistivity.

The tapeworm is an animal, and animal cells have no cell wall, only a cell membrane. A rigid cell wall lies outside the cell membrane in plants, fungi, most bacteria and many protists, giving the cell shape and protection.

Neutrons sit inside the nucleus with protons; it is the electrons that move around the nucleus. The neutron was discovered by James Chadwick in 1932, and he received the Nobel Prize in Physics for it in 1935.

Malaria is caused by the protozoan parasite Plasmodium, of which several species infect human beings, and it is transmitted by the bite of an infected female Anopheles mosquito, the male feeding on plant juices.

Iodine is a non-metal, yet its solid crystals have a shiny, metallic lustre, which makes it the standard exception taught in school chemistry.

Tendons are made of tightly packed parallel bundles of collagen fibres, which give them great pulling strength. Collagen is the most abundant protein in the human body.

Fluorine cannot be detected by Lassaigne's test, because silver fluoride is soluble in water and gives no precipitate. Lassaigne's test, or the sodium fusion test, detects nitrogen, sulphur and halogens in an organic compound.

This statement is false: enzymes are mostly proteins, but most proteins are not enzymes. Proteins do many jobs in the body.

As blood flows through the thin-walled capillaries, part of its plasma, with small proteins and some white blood cells, leaks out into the spaces between cells.

The thyroid gland needs iodine to make thyroxine, so iodized salt keeps this hormone in supply. Thyroxine (T4) contains four iodine atoms in each molecule, and the thyroid cannot make it without iodine from food.