A portable water-purification unit is tested. It transfers energy directly to water in a chamber. The water is heated to its boiling point, and the unit then continues to operate while some water becomes water vapour. Assume that all the energy transferred in each test is gained by the water.
| Quantity | Test A | Test B |
|---|---|---|
| Mass of water | 0.50 kg | 0.50 kg |
| Starting temperature | 20 ∘C20\ ^\circ\mathrm{C}20 ∘C | 80 ∘C80\ ^\circ\mathrm{C}80 ∘C |
| Energy transferred to the water | 4.20 × 105 J | 4.20 × 105 J |
The boiling point of water is 100 ∘C100\ ^\circ\mathrm{C}100 ∘C. The specific heat capacity of water is 4.20×103 J kg−1 ∘C−14.20\times10^3\ \mathrm{J\,kg^{-1}\,{}^\circ C^{-1}}4.20×103 Jkg−1∘C−1. The specific latent heat of vaporisation of water is 2.26 × 106 J/kg.
Calculate the mass of water converted to water vapour in test A.
Compare the mass of water converted to water vapour in test B with the mass in test A, and explain your answer.
110 exam-style questions on Edexcel GCSE Physics 14.2 Specific heat capacity and latent heat, covering 14.2.1 Heating, temperature and changes of state, 14.2.2 Specific heat capacity and specific latent heat, 14.2.3 Specific heat capacity calculation, 14.2.4 Specific latent heat calculation, and 14.2.5 Reducing energy transfer through thermal insulation. Each one has a worked solution and a mark scheme showing where the marks go.