Edexcel IGCSE Physics 2.15 Charge, current & time

Practise using Q = I x t to find charge, current or time in battery charging, lamp and spark contexts, with seconds, minutes and powers of ten.

Exam points

state or rearrange Q = I x t using standard symbols for charge, current and time
calculate charge, current or time from data, converting minutes and handling powers of ten
explain that a larger charging current transfers the same charge in a shorter time

[Maximum number: 4]

A student uses this apparatus to demonstrate the effect of electric charge.

Figure for Question 2.15 Charge, current and time question 1 — Edexcel IGCSE Physics

He pours some fine powder into a funnel.
The fine powder moves through a length of plastic tubing and falls into a metal can.
The metal can rests on a metal cap.
The metal cap is connected to a thin piece of metal via a metal rod.
When the powder lands in the can, the thin piece of metal moves away from the metal rod.

(a)

A coulombmeter measures electric charge.

The student connects a coulombmeter to the metal can.
When all the powder has landed in the can, the coulombmeter shows a reading of $-9.4 \times 10^{-9} \mathrm{C}$ .

[ 4 ]

(i)

State the formula linking charge, current and time.

[ 1 ]

(ii)

It takes a time of 12 s from when the powder starts landing in the metal can until all the powder has landed in the can.

Calculate the mean charging current.

mean charging current = ............ A

[ 3 ]

Marking points:
- substitution
- rearrangement
- evaluation

Example:
$-9.4\times10^{-9}=\text{current}\times12$ $\text{current}=\frac{-9.4\times10^{-9}}{12}$ $\text{current}=-7.8\times10^{-10}\ \mathrm{A}$

Accept:
- $7.83\ldots\times10^{-10}\ \mathrm{A}$

Marking guidance:
- power-of-ten error gives a 1 mark penalty

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2.15 Charge, current and time question 1

Question (a)

Question (i)

Question (ii)