The electric motor of a laboratory centrifuge is supplied with 1.5 kJ of energy while the rotor speeds up. The efficiency of the motor is 60%. Its useful output is the energy transferred to the kinetic energy store of the rotor, and all of its other output is transferred to the surroundings. The energy stored in the motor itself does not change.
Four records of the motor's energy transfers are proposed.
| Record | Useful transfer to rotor in kJ\mathrm{kJ}kJ | Unwanted transfers to surroundings in kJ\mathrm{kJ}kJ |
|---|---|---|
| 1 | 0.90 | 0.60 |
| 2 | 0.60 | 0.90 |
| 3 | 0.90 | 1.50 |
| 4 | 2.50 | 1.00 |
Which record correctly represents the motor's energy transfers?
Record 1
Record 3
Record 4
Record 2
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.