Physics, Units and the Solar System MCQs with Explanations

The ampere is one of the seven SI base units and measures electric current. The volt measures potential difference, the watt measures power and the coulomb measures charge; all three of these are derived units.

A light-year is the distance light travels through vacuum in one year, about 9.46 trillion kilometres (9.46 x 10^15 m), so it measures astronomical distance and never a length of time. The parsec, another unit of astronomical distance, equals about 3.26 light-years.

A barometer measures atmospheric pressure, commonly reported in millibars or in millimetres of mercury, and a falling reading usually signals changing or rainy weather. Humidity is measured by a hygrometer, the density of a liquid by a hydrometer and current by an ammeter.

Light travels at about 3 x 10^8 metres per second in vacuum, exactly 299,792,458 m/s, and it slows a little in water and in glass. The value 3 x 10^10 is the same speed expressed in centimetres per second, so always read the unit attached to each option.

Sound travels at about 343 m/s in air at room temperature, and at about 331 m/s at 0 degrees Celsius; it becomes faster in warmer air. In liquids and solids it is faster still, because the particles are closer together and pass on the vibration more readily.

The second law states that the rate of change of momentum of a body is proportional to the applied force, which reduces to F = ma when the mass is constant. The first law defines inertia, the third law pairs action with reaction, and gravitation gives the attraction between two masses.

Boyle's law states that pressure multiplied by volume stays constant when the temperature is fixed, which is why pulling back the plunger of a syringe enlarges the volume, lowers the pressure and draws fluid in. Charles's law instead links the volume of a gas to its temperature at constant pressure.

Water held behind the dam stores gravitational potential energy; as it falls this becomes kinetic energy, which turns a turbine coupled to a generator that produces electricity. The last option describes an electric motor, which runs the same conversion in reverse.

In myopia the image of a distant object is focused in front of the retina, and a diverging concave lens spreads the rays so the image falls on the retina. A converging convex lens corrects long-sightedness (hypermetropia), and a cylindrical lens is used for astigmatism.

Venus is the hottest planet, with a surface temperature of about 465 degrees Celsius, because its dense carbon dioxide atmosphere and clouds of sulphuric acid trap heat in a runaway greenhouse effect. Mercury lies closer to the Sun but has almost no atmosphere, so it cannot retain heat.

Jupiter is the largest planet, with a diameter about eleven times and a mass about 318 times that of Earth; it is a gas giant made chiefly of hydrogen and helium. Saturn is the second largest planet and is the one famous for its prominent rings.

Pluto was reclassified as a dwarf planet by the International Astronomical Union in 2006 because it has not cleared the neighbourhood of its orbit of other Kuiper Belt bodies. Ganymede and Europa are moons of Jupiter and Titan is a moon of Saturn, and the dwarf planet list also includes Ceres, Eris, Makemake and Haumea.

One revolution takes about 365.25 days, roughly 365 days and 6 hours, so the leftover quarter days accumulate into one extra day every four years. A lunar year of twelve months is only about 354 days, which is why a purely lunar calendar drifts against the seasons.

The neutron, which sits in the nucleus beside the proton, is electrically neutral and has very nearly the same mass as a proton. The electron carries a negative charge and the positron is its anti-particle with a positive charge, each of magnitude about 1.6 x 10^-19 coulomb.