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AQA · GCSE · Physics · Higher

Fuse Wire Mass from Latent Heat

Q10.4 4 marks

When the fuse wire is at its melting point, the additional energy needed to melt the wire is 1.02 J.

specific latent heat of fuse wire = 60 kJ/kg
thermal energy for a change of state = mass × specific latent heat, E=mLE=mL

Calculate the mass of the fuse wire.

Use the Physics Equations Sheet.

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Marking points

  1. 1 Converts 60 kJ/kg to 60 000 J/kg, or consistently converts energy to kJ.
  2. 2 Uses E = mL with the given energy and latent heat.
  3. 3 Rearranges correctly for mass.
  4. 4 Obtains 1.7 × 10^-5 kg, subject to official error-carried-forward guidance.

Full-mark answer

60 kJ/kg=60 000 J/kg60\text{ kJ/kg}=60\,000\text{ J/kg}. Using E=mLE=mL, m=E/L=1.02/60 000=1.7×10−5 kgm=E/L=1.02/60\,000=1.7\times10^{-5}\text{ kg}.

Why this answer loses marks

I divided the latent heat by the energy.

The mass is energy divided by specific latent heat, after making their energy units consistent.

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