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Specific Heat CapacityCambridge IGCSE Physics: Revision notes

Section 1

What Is Specific Heat Capacity?

Specific heat capacity is the energy required to raise the temperature of one kilogram of a substance by one degree Celsius (or one kelvin).

The equation is:

c = deltaE / (m x deltatheta)

where c is specific heat capacity, deltaE is the energy transferred, m is the mass, and deltatheta is the change in temperature.

Rearranged, this gives:

deltaE = m x c x deltatheta

Different substances have different specific heat capacities — water has an unusually high specific heat capacity, which is why it takes a lot of energy to heat up (and a lot of energy to cool down).

Key termsspecific heat capacity
Example

To raise the temperature of 2 kg of water (specific heat capacity 4200 J/(kg degreeC)) by 10 degreesC: deltaE = 2 x 4200 x 10 = 84,000 J.

Common mistake

Forgetting to convert mass into kilograms, or using the temperature in degrees Celsius directly as the mass, are common calculation errors — check units carefully before substituting.

Section 2

Rise in Temperature and Internal Energy

A rise in the temperature of an object increases its internal energy. At the particle level, an increase in temperature is described as an increase in the average kinetic energy of all the particles in the object.

This is why supplying energy to a substance (for example, by heating it) raises its temperature: the energy increases the kinetic energy of the particles, which we measure as a temperature rise.

Key termsinternal energy

Section 3

How Do You Measure the Specific Heat Capacity of a Solid?

  1. Measure the mass of a solid block (often aluminium or copper) using a balance.
  2. Insert an electrical heater and a thermometer into holes drilled in the block.
  3. Record the starting temperature of the block.
  4. Switch on the heater for a measured time, recording the current and voltage (or using a joulemeter) to calculate the energy supplied.
  5. Record the highest temperature reached and calculate the temperature rise.
  6. Calculate specific heat capacity using c = deltaE / (m x deltatheta), where deltaE is the electrical energy supplied.
Exam tip

Insulating the block with lagging reduces energy losses to the surroundings, giving a more accurate value of specific heat capacity.

Section 4

How Do You Measure the Specific Heat Capacity of a Liquid?

  1. Measure a known mass of the liquid into an insulated container.
  2. Place an electrical heater and a thermometer directly into the liquid.
  3. Record the starting temperature.
  4. Switch on the heater for a measured time, recording the electrical energy supplied (from current, voltage and time, or a joulemeter).
  5. Stir the liquid gently and continuously to keep the temperature even throughout.
  6. Record the highest temperature reached and calculate specific heat capacity using the same equation as for a solid.
Example

Stirring is essential for a liquid experiment (but not usually needed for a solid) because liquids do not conduct heat evenly on their own — without stirring, the thermometer might read a temperature that is not representative of the whole liquid.

Must Know

  • Specific heat capacity (c): the energy required to raise the temperature of 1 kg of a substance by 1 degreeC.
  • Equation: c = deltaE / (m x deltatheta), rearranged as deltaE = m x c x deltatheta.
  • A rise in temperature increases an object's internal energy, corresponding to an increase in the average kinetic energy of its particles.
  • Specific heat capacity of a solid is found using an electrical heater and thermometer inserted into a measured mass of the solid.
  • Specific heat capacity of a liquid is found the same way, but the liquid must be stirred continuously for an even temperature.
  • Water has an unusually high specific heat capacity, meaning it needs a lot of energy to heat up or cool down.

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