A deep-sea research probe uses a high-intensity LED strobe light powered by a lithium-ion cell pack.
State the equation that relates charge flow (QQQ), current (III), and time (ttt).
During a test run, the strobe light is activated continuously for 18 000 s18\,000\text{ s}18000 s. The mean current passing through the LED is 65 mA65\text{ mA}65 mA. Calculate the total charge flow through the LED during this test.
While servicing the probe, a technician installs the lithium-ion cell pack backward. Explain why the strobe light fails to operate.
State the equation that links efficiency, total power input, and useful power output.
The total electrical power input to the LED strobe is 0.35 W0.35\text{ W}0.35 W. The LED operates at an efficiency of 0.720.720.72. 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.