Page 31 - Physics_Form_2

Static electricity

Questions
Q (C)
max (a) Plot a graph of current
against time.
(b) What does the area
Charge on capacitor represent?
under the graph
FOR ONLINE READING ONLY

The area under the current
(I) versus time (t) graph
represents the charge (Q).
When a cell is connected
O Time (s) to a circuit, electrons
flow accumulating on the
Figure 1.33: Graph of the charge against time for a plate connected to the
charging capacitor
negative terminal, while the
The resistance, R, controls the current in the circuit. opposite plate experiences
Potential difference acrossthecell less accumulation due to
Initial charging current =
Resistance inthecell attraction from the positive
The gradient of the charging curve gives the current. terminal. Charging continues
Therefore, the initial current is the gradient of the until the potential difference
graph at the origin (time = 0). (p.d.) between the plates
equals the total potential
difference across the cell, at
Activity 1.10 which point the current drops

Aim: To demonstrate the charging of a to zero. The capacitor stores
capacitor equal but opposite charges,
Materials: a cell, an uncharged capacitor, a high- +Q and -Q, on its plates.
resistance voltmeter, a resistor, a switch,
connecting wires and an ammeter Discharging a capacitor
Procedure Theoretically, an isolated
1. Connect the circuit as in Figure 1.32, keeping the but charged capacitor should
switch open. hold its charge indefinitely.
2. Close the switch and then record the values of However, due to leakage
current at different time intervals. between the plates, the
3. Tabulate your results as follows: capacitor is eventually
discharged. A capacitor
Time (s) 0 20 30 40 50 60 70 80 90 can also be discharged by
Current (mA) connecting its plates to a

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Physics Form 2 Final.indd 25 25/10/2025 10:25