General Science Previous Year Questions (PYQ) with Answers – Page 37

Outside a long straight wire, the field is B = μ₀I/(2πr), so doubling the distance halves the field. This result follows from Ampère's circuital law, or from the Biot–Savart law applied to a long wire.

Sugar dissolves in water as whole, neutral molecules and releases no ions, so its solution does not conduct electricity. A solution conducts only when it contains free ions that can carry charge between the electrodes.

Electric power equals voltage times current, so the current is 60 W ÷ 240 V = 0.25 A. The relation P = VI comes straight from the definitions: voltage is energy per unit charge and current is charge per second, so their product is energy per second, or power.

Its density is about 0.86 g/cm³, less than that of water, so it floats while it reacts. Potassium is an alkali metal, soft enough to cut with a knife.

Hydrogen has three isotopes: protium with one proton and no neutron, deuterium with one neutron, which gives heavy water, and tritium with two neutrons, which is radioactive and is used in fusion research and in luminous dials.

Iron is needed to make haemoglobin, so too little iron means too little haemoglobin and a reduced ability of the blood to carry oxygen.

Without enough vitamin D the body cannot absorb calcium and phosphorus properly, so a child's growing bones stay soft and bend.

Urea is the body's way of getting rid of the nitrogen that comes from breaking down proteins, and only proteins among these contain nitrogen.

This follows the reactivity series of metals, in which zinc lies above iron, iron above lead and lead above copper.

One hertz means one complete cycle per second, so a frequency of 3 Hz means the current completes three full cycles every second.

Pitch is how the ear perceives the frequency of a sound, so a higher pitch means more vibrations per second.

Green plants use sunlight, carbon dioxide and water to make glucose, giving out oxygen as a by-product. Photosynthesis takes place mainly in the chloroplasts of leaf cells, where chlorophyll traps light energy.

Both work in neutral to alkaline conditions, in the mouth and the small intestine, and stop working in the acid of the stomach.

The cell membrane is flexible, and this lets a cell fold it around food and other material and take it in.

Chlorophyll absorbs light energy, which is used to split water and then to reduce carbon dioxide to sugar. In the light reactions, energy trapped by chlorophyll splits water molecules (photolysis), releasing oxygen, hydrogen ions and electrons and producing ATP and NADPH.

In Einstein's special theory of 1905 the energy required to accelerate a body with mass rises without limit as its speed approaches that of light, so such a body can come close to but never reach the speed of light in vacuum, which is the same for every observer.

Their valencies are neon 0, magnesium 2, nitrogen 3 and silicon 4. Valency is the combining capacity of an atom, the number of electrons it loses, gains or shares to reach a stable octet.

Electric power is P = V × I, and 220 V × 0.6 A = 132 W. Power is the rate at which electrical energy is used, measured in watts; one watt is one joule per second, or one volt times one ampere.

Argon has atomic number 18, and a neutral atom has as many electrons as protons, so it has 18 electrons.

X-rays have wavelengths of roughly 0.01 nm to 10 nm, so 1 nm sits right inside the X-ray band. The electromagnetic spectrum runs, from the shortest wavelength to the longest, as gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves and radio waves.