Specific Heat Capacity (Cambridge (CIE) IGCSE Physics): Revision Note

Internal energy

• A rise in the temperature of an object increases its internal energy

  • This can be thought of as due to an increase in the average speed of the particles

  • Increasing speed increases kinetic energy

• Internal energy is defined as:

The total energy stored inside a system by the particles that make up the system due to their motion and positions

• Motion of the particles affects their kinetic energy

• Positions of the particles relative to each other affects their potential energy

  • Together, these two make up the internal energy of the system

Average kinetic energy

Extended Tier Only

• Heating a system changes a substance's internal energy by increasing the kinetic energy of its particles

  • The temperature of the material, therefore, is related to the average kinetic energy of the molecules

• An increase in temperature leads to an increase of the average kinetic energy of the particles in the substance

  • This also means that internal energy increases, as internal energy is the sum of all kinetic and potential energies

Specific heat capacity

Extended Tier Only

What is specific heat capacity?

• When heated, a substance's temperature can increase 

• The amount by which the temperature increases depends on:

  • The mass of the substance heated

  • The type of material

  • The amount of thermal energy transferred into the system

• The specific heat capacity, c, of a substance is defined as:

 The energy required per unit mass per unit temperature increase

• In other words, this is the amount of energy required to raise the temperature of 1 kg of a substance by 1 °C

• Different substances have different specific heat capacities

  • If a substance has a low specific heat capacity, it heats up and cools down quickly (i.e. it takes less energy to change its temperature)

  • If a substance has a high specific heat capacity, it heats up and cools down slowly (i.e. it takes more energy to change its temperature)

Calculating specific heat capacity

• The amount of energy needed to raise the temperature of a given mass by a given amount can be calculated using the equation:

$c=\frac{\mathrm{\Delta }E}{m\mathrm{\Delta }\theta }$    

• Where:

  • ΔE = change in thermal energy, in joules (J)

  • m = mass, in kilograms (kg)

  • c = specific heat capacity, in joules per kilogram per degree Celsius (J/kg °C)

  • Δθ = change in temperature, in degrees Celsius (°C)