General Science Mixed Quiz: Set 4

The candela takes its name from the candle, which was once used as a rough standard of light, and it is one of the seven base units of the SI system.

In diamond every carbon atom is joined to four other carbon atoms by strong covalent bonds. These bonds point towards the corners of a tetrahedron and build a rigid three-dimensional network that runs through the whole crystal.

Magnification is a ratio of two lengths, so the units cancel and it is a pure number. For a mirror or a lens, magnification m equals the height of the image divided by the height of the object (h′/h).

Air always moves from a region of higher pressure to one of lower pressure, so it flows out of the lungs only when the pressure inside them rises above that of the outside air.

An iron, toaster, oven, kettle and heater all turn electrical energy into heat when current flows through a coil of high resistance.

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.

The symbol of potassium is K, from its Latin name kalium; Po is the symbol of polonium, the radioactive element discovered by Marie Curie in 1898 and named after Poland.

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

Nitrogen is an unreactive gas, so it drives the oxygen out of the packet and stops the oil in the chips from getting oxidised.

All three are genetic disorders, caused by changes in genes or chromosomes and passed on through birth, not by germs.

Washing soda is sodium carbonate decahydrate: each unit of sodium carbonate holds ten molecules of water of crystallisation. It is made from common salt in steps: baking soda is heated to get anhydrous sodium carbonate, called soda ash, which is then recrystallised from water to give washing soda crystals.

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

Bronze is made by melting copper and tin together, with copper as the main metal. It is harder than pure copper and does not corrode easily, so it has been used for statues, bells, medals and utensils for thousands of years.

The cooking temperature is set by the pressure inside the cooker, and that pressure is fixed by the weight sitting on the vent and the area of the hole under it.

The rough strip of a safety matchbox is coated with powdered glass and a little red phosphorus, while the head of the matchstick carries antimony trisulphide and potassium chlorate.

A healthy human ear can hear sound waves with frequencies from about 20 hertz to 20,000 hertz (20 kHz); this band is called the audible range.

The Golgi apparatus is the main site where glycoproteins and glycolipids are formed. It is a stack of flat, disc-shaped sacs called cisternae, first described by Camillo Golgi in 1898.

A red blood cell is a biconcave disc, thin in the middle and thick at the edge, not an amoeboid cell.

The medulla oblongata is the breathing centre of the brain, which is why we keep breathing even while asleep. It is the lowest part of the hindbrain and joins the brain to the spinal cord.

Pellagra is caused by a lack of vitamin B3, niacin, also called nicotinic acid, and is remembered by the three Ds: dermatitis, a rough dark rash on skin exposed to sunlight, diarrhoea from the gut, and dementia from the nervous system; untreated, a fourth D, death, follows.