An electric heating element is used to raise the temperature of a fixed mass of water by 15 ∘C15\text{ }^\circ\text{C}15 ∘C.
The student then increases the electrical input power to the heating element, keeping the efficiency of the heating process constant, and repeats the experiment to achieve the same temperature rise.
Which row in the table correctly describes the effect of increasing the input power on the useful thermal energy transferred to the water and the time taken to heat it?
| Useful energy transferred to water | Time taken to heat the water | |
|---|---|---|
| A | decreases | decreases |
| B | stays the same | stays the same |
| C | stays the same | decreases |
| D | increases | decreases |
Useful energy: decreases | Time taken: decreases
Useful energy: stays the same | Time taken: stays the same
Useful energy: stays the same | Time taken: decreases
Useful energy: increases | Time taken: decreases
528 exam-style questions on CIE IGCSE Physics 2.2 Thermal properties and temperature, covering 2.2.1 Thermal expansion of solids, liquids and gases, 2.2.2a Internal energy and temperature, 2.2.2b Specific heat capacity, 2.2.3a Melting, boiling, condensation and solidification, 2.2.3b Evaporation, and 2.2.3c Cooling by evaporation. Each one has a worked solution and a mark scheme showing where the marks go.