A student compares two electric kettles.
The Table shows the energy transfers when each kettle is used to boil some water.
Table
| Kettle | Total energy supplied in kJ\text{kJ}kJ | Energy transferred to the thermal store of the water in kJ\text{kJ}kJ |
|---|---|---|
| A | 200 | 170 |
| B | 150 | 132 |
Calculate the efficiency of each kettle and state which kettle is more efficient.
The student says:
'Kettle A is more efficient because it transfers more energy to the water.'
Explain why the student is wrong.
The student tests a third kettle and calculates its efficiency as 1.2.
Explain why this value must be wrong.