CIE IGCSE Physics

Revision Notes

2.2.2 Specific Heat Capacity

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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

      Internal Energy in Water, downloadable AS & A Level Physics revision notes

      Substances have internal energy due to the motion of the particles and their positions relative to each other

Average Kinetic Energy

EXTENDED

    

  • 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

    

  • This increase in kinetic energy (and therefore internal energy) can:
    • Cause the temperature of the system to increase
    • Or, produce a change of state (solid to liquid or liquid to gas)

Change in internal energy, downloadable AS & A Level Physics revision notes

As the container heats up, the gas molecules move faster

Faster motion causes higher kinetic energy and therefore higher internal energy

Specific Heat Capacity

EXTENDED

   

  • How much the temperature of a system increases depends on:
    • The mass of the substance heated
    • The type of material
    • The amount of thermal energy transferred in to the system

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

The amount of energy required to raise the temperature of 1 kg of the 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 (ie. it takes less energy to change its temperature)
    • If a substance has a high specific heat capacity, it heats up and cools down slowly (ie. it takes more energy to change its temperature)

Specific heat examples, downloadable AS & A Level Physics revision notes

Low vs high specific heat capacity

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:

straight capital delta E space equals space m c straight capital 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)

Worked example

Water of mass 0.48 kg is increased in temperature by 0.7 °C. The specific heat capacity of water is 4200 J / kg °C.

Calculate the amount of thermal energy transferred to the water.

Step 1: Write down the known quantities

    • Mass, m = 0.48 kg
    • Change in temperature, ΔT = 0.7 °C
    • Specific heat capacity, c = 4200 J/kg °C

Step 2: Write down the relevant equation 

straight capital delta E space equals space m c straight capital delta theta

Step 3: Calculate the thermal energy transferred by substituting in the values

straight capital delta E space equals space left parenthesis 0.48 right parenthesis space cross times space left parenthesis 4200 right parenthesis space cross times space left parenthesis 0.7 right parenthesis space equals space 1411.2

Step 4: Round the answer to 2 significant figures and include the units

ΔE = 1400 J

   

Exam Tip

You will always be given the specific heat capacity of a substance, so you do not need to memorise any values.

However, it's useful to have the general idea that, the larger the number, the less the substance will increase in temperature for a given amount of heat.

You can see this for yourself in your own kitchen at home. Metal pans, which have a relatively low specific heat capacity get very hot, very quickly when put on the hob. Add water to the pan, which has a relatively high specific heat capacity and the water will take much longer to heat up.

Notice the units of specific heat capacity:

 joules per kilogram per degree Celsius  : J / kg °C

'per' means 'divided by'. We say 'per' in front of every value that is being divided by, hence 'per kilogram per degree Celsius'

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Lindsay Gilmour

Author: Lindsay Gilmour

Lindsay graduated with First Class Honours from the University of Greenwich and earned her Science Communication MSc at Imperial College London. Now with many years’ experience as a Head of Physics and Examiner for A Level and IGCSE Physics (and Biology!), her love of communicating, educating and Physics has brought her to Save My Exams where she hopes to help as many students as possible on their next steps.