Specific Heat Capacity (CIE A Level Physics)

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

The amount of thermal energy required to raise the temperature of 1 kg of a substance by 1 °C

• This quantity determines the amount of energy needed to change the temperature of a substance
• The specific heat capacity is measured in units of Joules per kilogram per Kelvin (J kg^-1 K^-1) or Joules per kilogram per Celsius (J kg^-1 °C^-1) and has the symbol c
  • Different substances have different specific heat capacities
  • Specific heat capacity is mainly used in liquids and solids

Specific heat capacity of different materials

Low v high specific heat capacity.

• From the definition of specific heat capacity, it follows that:
  • The heavier the material, the more thermal energy that will be required to raise its temperature
  • The larger the change in temperature, the higher the thermal energy will be required to achieve this change

Calculating specific heat capacity

• The amount of thermal energy Q needed to raise the temperature by Δθ for a mass m with specific heat capacity c is equal to:

ΔQ = mcΔθ

• Where:
  • ΔQ = change in thermal energy (J)
  • m = mass of the substance you are heating up (kg)
  • c = specific heat capacity of the substance (J kg^-1K^-1or J kg^-1 °C^-1)
  • Δθ = change in temperature (K or °C)

• If a substance has a low specific heat capacity, it heats up and cools down quickly
• If a substance has a high specific heat capacity, it heats up and cools down slowly
• The specific heat capacity of different substances determines how useful they would be for a specific purpose eg. choosing the best material for kitchen appliances

Table of values of specific heat capacity for various substances

• Good electrical conductors, such as copper and lead, are also excellent conductors of heat due to their low specific heat capacity