A transformer supplies lamps in a museum display and is 100% efficient. Its primary potential difference is 230 V and its secondary potential difference is 11.5 V. The secondary current changes when some lamps are switched off.
| Display state | Secondary current |
|---|---|
| Before lamps are switched off | 8.0 A |
| After lamps are switched off | 2.0 A |
What is the decrease in the primary current?
0.10 A0.10\ \mathrm{A}0.10 A
6.0 A6.0\ \mathrm{A}6.0 A
120 A120\ \mathrm{A}120 A
0.30 A0.30\ \mathrm{A}0.30 A
108 exam-style questions on Edexcel GCSE Physics 13.2 Transformers and the National Grid, covering 13.2.1 Transformers and induction, 13.2.2 The transformer turns-ratio equation, 13.2.3 The National Grid, 13.2.4 The transformer power equation, and 13.2.5 Advantages of high-voltage transmission. Each one has a worked solution and a mark scheme showing where the marks go.