Leaving Cert Physics — Example Quiz

Acceleration is the change in velocity divided by time: (20 − 0) ÷ 8 = 2.5 m s⁻². Multiplying rather than dividing gives the distractor 160, which is why the units are worth checking — m s⁻¹ divided by s gives m s⁻².

A vector has both magnitude and direction. Velocity is speed in a stated direction, so it is a vector; speed alone is scalar. Mass and energy are scalars. This distinction matters because two objects can have equal speed and opposite velocity.

False. Weight is the force of gravity on a mass, W = mg. The Moon's gravitational field strength is about one sixth of Earth's, so weight is about one sixth. Mass is what stays the same — it is a measure of the amount of matter.

From Ohm's law, V = IR = 3 × 4 = 12 V. Dividing instead of multiplying produces the two smaller distractors, and adding produces 7.

In a transverse wave the oscillation is perpendicular to the direction of travel — true of light and of water surface waves. Sound in air, including ultrasound, is longitudinal: the air oscillates along the direction of travel as compressions and rarefactions.

The wave equation gives c = fλ = 50 × 4 = 200 m s⁻¹. Dividing frequency by wavelength gives 12.5, a common slip when the equation is recalled the wrong way round.

Red is at the long-wavelength, low-frequency end of the visible spectrum; violet is at the short-wavelength, high-frequency end. Because c = fλ is fixed for light in a vacuum, the longest wavelength necessarily has the lowest frequency.

The order by increasing frequency is radio, microwave, infrared, visible, ultraviolet, X-ray, gamma. Increasing frequency means decreasing wavelength and increasing photon energy, which is why X-rays are ionising and radio waves are not.

Power is the rate of doing work, measured in watts, where one watt is one joule per second. The joule is the unit of energy, the newton of force, and the pascal of pressure.

True. A series circuit provides only one path, so charge cannot accumulate anywhere and the current is identical throughout. It is the potential difference that divides between the components, summing to the supply voltage.

Gamma radiation is high-energy electromagnetic radiation, stopped only by thick lead or concrete. Beta particles are stopped by a few millimetres of aluminium, and alpha particles by paper or a few centimetres of air. The order of penetration is the reverse of the order of ionising power.

Potential energy gained is mgh = 2 × 10 × 5 = 100 J. Omitting g gives 10 J, and it is worth noting that this is the gain in potential energy — the total depends on where the zero is taken.

Refraction is caused by a change in the speed of light between media, and since frequency is set by the source and does not change, the wavelength must change instead. Light entering along the normal (at 90° to the surface) slows down but does not change direction.

In the negative temperature coefficient thermistors used at this level, resistance falls sharply as temperature rises, because more charge carriers are released. This behaviour is the opposite of a metallic conductor, whose resistance increases with temperature.

The third law concerns paired forces acting on different bodies. A is the second law, B is the first. The key point often missed is that the action and reaction act on different objects, which is why they do not cancel out.

The coulomb is the unit of electric charge. Current is measured in amperes, where one ampere is one coulomb per second; potential difference in volts; resistance in ohms.

False. Sound is a mechanical wave and requires a medium whose particles can be compressed and rarefied. A vacuum has no such particles, which is why a ringing bell inside an evacuated jar becomes inaudible while remaining visible — light needs no medium.

Power is work divided by time: 600 ÷ 30 = 20 W. Multiplying gives 18000, and inverting the fraction gives 0.05.

Specific heat capacity is per kilogram, per kelvin. Options B and C describe the specific latent heats of fusion and vaporisation, which occur at constant temperature. Option D omits the fixed mass, which is what makes the quantity "specific".

There is a threshold frequency below which no electrons are emitted regardless of how intense the light is. This was the observation that classical wave theory could not explain and that Einstein accounted for with photons, each carrying energy E = hf.