Fig. 6.1 presents the circuit diagram of a flashlight (torch). The electromotive force (e.m.f.) of the battery is $4.5\,\text{V}$. A $60\,\Omega$ fixed resistor is included in the circuit. The current in the light-emitting diode (LED) is $0.020\,\text{A}$.
(a)[2]
Calculate the potential difference (p.d.) across the LED.
(b)[1]
Explain why the LED does not light up if the battery is reversed.
(c)[2]
Show that the flashlight runs for approximately $3\,\text{h}$.
(d)[2]
Calculate the total charge that passes through the LED in $3600\,\text{s}$.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “Potential difference across LED = 3.3 V” …