During the water-heating stage of a dishwasher, heating the water is the useful output. The data for one cycle are shown in the table.
| Quantity | Value |
|---|---|
| total energy input during the stage | 1.5 MJ1.5\ \text{MJ}1.5 MJ |
| efficiency of the stage | 0.80 |
A layer of thermal insulation surrounds the water compartment. A newer design uses a thicker layer of the same material.
Calculate the useful energy transferred to the water in one cycle.
Use the equation
Euseful=ηEtotal E_{\text{useful}}=\eta E_{\text{total}} Euseful=ηEtotalState the effect of using the thicker layer on:
(i) the rate of energy transfer from the water compartment to the surroundings
(ii) the efficiency of the water-heating stage.
100 exam-style questions on Edexcel GCSE Physics 3.2 Dissipation and efficiency, covering 3.2.1 Dissipation of energy, 3.2.2 Reducing unwanted energy transfers, 3.2.3 Efficiency, and 3.2.4 Increasing efficiency. Each one has a worked solution and a mark scheme showing where the marks go.