Electricity: Question 1

Worked solution

Part (a): Charge delivered

Charge, current and time are related by: $Q = It$

First convert the time to seconds: $t = 40.0\text{ min} = 40.0 \times 60 = 2400\text{ s}$

Substituting $I = 1.50\text{ A}$ and $t = 2400\text{ s}$: $Q = 1.50 \times 2400 = 3600\text{ C}$

So the charge delivered is $\boxed{3600}\text{ C}$.

Part (b): Number of electrons

Charge is carried by discrete electrons, so the total charge is related to the number of electrons $n$ and the charge on one electron $e$ by: $Q = ne \implies n = \frac{Q}{e}$

Substituting $Q = 3600\text{ C}$ and $e = 1.60\times10^{-19}\text{ C}$: $n = \frac{3600}{1.60\times10^{-19}} = 2.25\times10^{22}$

So $\boxed{2.25\times10^{22}}$ electrons flow through the charger.

Part (c): Meaning of electric current

Electric current is the rate of flow of (electric) charge past a given point in a circuit. That is, the amount of charge passing a point per unit time. Equivalently, in a metallic conductor it is the flow of free (delocalised) electrons, which act as the charge carriers, drifting slowly through the conductor while being driven by the electric field set up by the source.

Final answers

• (a) Charge delivered $=$ $3600\text{ C}$
• (b) Number of electrons $=$ $2.25\times10^{22}$
• (c) Electric current is the rate of flow of charge (charge carriers) past a point in a circuit.