Enter the data you recorded during the capacitor charging experiment into the graph plot.

Use the cursor to analyse the graph at various points to work out the function described by each graph.

(1) Which function best describes the current/time graph?

(2) Which function best describes the capacitor voltage/time graph?

(3) What would a graph of charge/time look like?

Use the graph to find the initial value of the current, I₀. Record this on your worksheet.

Now find the times taken for the current to fall to 1/2(I₀), 1/4(I₀) and 1/8(I₀). Record these on the worksheet also. Can you spot a pattern?

The time taken for I to reach 1/2(I₀) is called the half-life, T_½. The fall from 1/2(I₀) to 1/4(I₀) is a further half-life and so the time taken is the same as from I to 1/2(I₀). Similarly the time taken for the current to fall from 1/4(I₀) to 1/8(I₀) is one half-life, T_½.

Two equations have been provided in responses to previous questions:

I = I₀e^-t/CR and  V_c = V_s(1 - e^-t/CR)

Each has a common term, CR. How is this significant?

Calculate the value of C×R, using the data from the circuit diagram.

Now use the capacitor voltage graph to work out V_c at

t = 1CR
t = 2CR
t = 3CR
t = 4CR
t = 5CR

Can you spot a pattern?

The term is called the time constant. After one time constant the voltage has reached 0.63 of its final value.

After a second time constant the voltage will have reached a further 0.63 of what was left after one time constant.

The capacitor is fully charged after about five time constants.

(4) What value would Q, the charge on the capacitor, have after t = CR?

(5) What effect do you think a larger resistor would have on the charging process?