National 5PhysicsSQARevision NotesProperties Of MatterSpecific Heat CapacityHeat Transfer

Heat Transfer (SQA National 5 Physics): Revision Note

Exam code: X857 75

Leander Oates

Written by: Leander Oates

Reviewed by: Katie M

Updated on

Heat transfer

Energy cannot be created or destroyed, it can only be converted from one form to another

  • This means that in energy calculations, all the energy must be accounted for

  • Energy can be:

    • transferred from one object to another

    • converted from one form to another

    • dissipated to the surroundings

  • Energy transfers can be applied to both heating and cooling

    • The same amount of energy required to heat a known mass of a substance by 1 °C will be dissipated to the surroundings as the substance cools by 1 °C

Worked Example

100.0g of water is cooled in a fridge from 20.0 °C to 5.00 °C.

The specific heat capacity of water is 4180 J kg-1 °C-1.

Determine the amount of electrical energy used by the fridge to cool the water.

Answer:

Step 1: Convert the mass of water to SI units

100 space straight g space cross times space fraction numerator 1 space kg over denominator 1000 space straight g end fraction space equals space 0.100 space kg

Step 2: Determine the change in temperature

increment T space equals space 20.0 space minus space 5.00

increment T space equals space 15.0 space degree straight C

Step 3: Apply the principle of conservation of energy

  • The electrical energy used by the fridge to cool the water is equal to the magnitude of the heat energy transferred away from the water

E subscript f r i d g e end subscript space equals space E subscript h space equals space c m increment T

Step 4: Substitute in the known values to calculate

E subscript f r i d g e end subscript space equals space c m increment T

E subscript f r i d g e end subscript space equals space 4180 space cross times space 0.100 space cross times space 15.0

E subscript f r i d g e end subscript space equals space 6270 space straight J

Examiner Tips and Tricks

Remember to always round your final answer to the correct number of significant figures, and to provide the unit. Students often lose marks in the exam for not doing so.

Remember that the calculated value can only be given to the same precision as the least precise value used in the calculation.

The least precise input value in this worked example is 3 s.f.; the answer is also given to 3 s.f.

Unlock more, it's free!

Join the 100,000+ Students that ❤️ Save My Exams

the (exam) results speak for themselves:

    Previous:Mean Kinetic EnergyNext:Specific Latent Heat
    Author
    Reviewer
    Leander Oates

    Author: Leander Oates

    Expertise: Physics Content Creator

    Leander graduated with First-class honours in Science and Education from Sheffield Hallam University. She won the prestigious Lord Robert Winston Solomon Lipson Prize in recognition of her dedication to science and teaching excellence. After teaching and tutoring both science and maths students, Leander now brings this passion for helping young people reach their potential to her work at SME.

    Katie M

    Reviewer: Katie M

    Expertise: Physics Content Creator

    Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.