General Science Previous Year Questions (PYQ) with Answers – Page 73

Potential difference is the work done to move a unit charge between two points, and its SI unit is the volt.

The N shell is the fourth shell (n = 4), and the most electrons a shell can hold is given by the formula 2n², so 2 × 4² = 32.

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.

It is the standard set of rules used for reflection by spherical mirrors and for the mirror formula. Under this convention the pole of the mirror is the origin and the principal axis is the x-axis.

Violet has the shortest wavelength in visible light, so glass slows it the most and bends it the most. White light is a mix of seven colours, remembered as VIBGYOR.

Each metal here is paired with one of its best-known ores. Bauxite is hydrated aluminium oxide; alumina is refined from it and then broken down by electrolysis in the Hall-Héroult process.

The number 235 is the mass number and uranium's atomic number is 92, so the nucleus holds 235 minus 92, that is 143 neutrons.

When light travels from a denser medium to a rarer one and strikes the boundary at an angle greater than the critical angle, it does not pass out at all but is reflected completely back.

Pressure is force acting per unit area, so its SI unit is the newton per square metre, which is given the special name pascal (Pa) after the French scientist Blaise Pascal, who stated the law of transmission of pressure in liquids used in hydraulic brakes and lifts.

During a sprint the muscles need energy faster than the blood can supply oxygen, so they switch to anaerobic respiration and lactic acid builds up.

Amphibians and most reptiles have a heart with three chambers: two atria and one ventricle. In frogs and toads, oxygen-rich blood from the lungs and oxygen-poor blood from the body both reach the single ventricle, so some mixing takes place.

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 English engineer Thomas Savery patented a steam pump in 1698 and called it the Miner's Friend, as it was meant to pump water out of flooded mines.

All three kinds of wave reflect, carry energy and exert pressure, but only electromagnetic waves can travel through a vacuum.

A light year is the distance light travels in empty space in one year, so despite its name it measures length, not time.

The power turned into heat in a wire carrying a current I is P = I²R, and the resistance of a wire is R = ρl/A, where ρ is the resistivity of its material.

The field at the centre of a coil is proportional to the number of turns and inversely proportional to the radius, so doubling N and halving R makes it four times larger.

RNA is usually single-stranded and its sugar, ribose, carries an extra hydroxyl group, which makes the molecule more reactive and easier to break or alter than double-stranded DNA.

For a real object anywhere in front of it, a convex mirror always gives a virtual, erect and diminished image.

A plane mirror always forms an image that stands upright, cannot be caught on a screen, and has its left and right sides swapped.