Question 1

What is the particle model in physics?

Accepted Answer

The particle model is a way of describing the behaviour of solids, liquids, and gases by considering the arrangement and movement of tiny particles (atoms or molecules). It explains properties like shape, volume, density, and how substances change state when heated or cooled. The model assumes particles are in constant motion and have forces between them.

Question 2

How do you calculate density?

Accepted Answer

Density is calculated using the formula: density = mass / volume. Mass is measured in kilograms (kg) or grams (g), and volume in cubic metres (m³) or cubic centimetres (cm³). For example, if a block has a mass of 200 g and a volume of 100 cm³, its density is 2 g/cm³. You can also use the formula ρ = m/V.

Question 3

What is the difference between specific latent heat of fusion and vaporisation?

Accepted Answer

Specific latent heat of fusion is the energy required to change 1 kg of a substance from solid to liquid (or vice versa) without changing temperature. Specific latent heat of vaporisation is the energy required to change 1 kg from liquid to gas (or vice versa). For water, the specific latent heat of fusion is 334 kJ/kg, and of vaporisation is 2260 kJ/kg – much larger because breaking all bonds to form a gas takes more energy.

Question 4

Why does temperature stay constant during melting?

Accepted Answer

During melting, the energy supplied is used to overcome the forces holding particles in a fixed lattice structure, not to increase their kinetic energy. This means the average kinetic energy (and thus temperature) remains constant until all the solid has melted. The same applies during boiling, where energy is used to separate particles into a gas.

Question 5

How does the particle model explain gas pressure?

Accepted Answer

Gas pressure is caused by particles colliding with the walls of their container. Each collision exerts a tiny force, and the sum of all collisions creates pressure. If you heat a gas, particles move faster and collide more frequently and with greater force, increasing pressure. If you decrease the volume, particles hit the walls more often, also increasing pressure.

Question 6

What is internal energy?

Accepted Answer

Internal energy is the total energy stored inside a substance due to the kinetic energy of its particles (their movement) and potential energy (from forces between particles). When you heat a substance, its internal energy increases. This can cause a rise in temperature (increasing kinetic energy) or a change of state (increasing potential energy).

Topic 14 – Particle model

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Topic 12 – Magnetism and the motor effect

How to Revise Topic 14 – Particle model — Edexcel GCSE Physics

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