A battery-powered ventilation fan is used to move air through a room.
The table shows the energy transfers during one test.
| Energy transfer | Energy transferred in J |
|---|---|
| to the kinetic energy store of the moving air | 420 |
| to the thermal energy stores of the fan and surroundings | 120 |
| to the surroundings by sound | 60 |
The bearings in the fan are then lubricated and the test is repeated with the same total energy supplied. In the second test, 90 J is transferred to the thermal energy stores of the fan and surroundings. The energy transferred by sound is unchanged.
Calculate the efficiency of the fan in the second test.