A bicycle safety light contains an LED, a switch, and two cells connected in series.
Write down the equation which links charge flow (QQQ), current (III), and time (ttt).
The bicycle safety light was left on for 21 600 s21\,600\text{ s}21600 s. The current in the LED was 45 mA45\text{ mA}45 mA. Calculate the total charge flow through the LED during this time.
After the cells were recharged, they were put back into the bicycle light the wrong way around. Explain why the light did not work.
Write down the equation which links efficiency, total power input, and useful power output.
The total power input to the LED is 0.18 W0.18\text{ W}0.18 W. The efficiency of the LED is 0.800.800.80. Calculate the useful power output of the LED.
39 exam-style questions on AQA GCSE Physics 2.1 Current, potential difference and resistance, covering 2.1.1 Standard circuit diagram symbols, 2.1.2 Electrical charge and current, 2.1.3 Current, resistance and potential difference, and 2.1.4 Resistors. Each one has a worked solution and a mark scheme showing where the marks go.