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The circuit below is being used to show the exponential charge or discharge of a capacitor through a resistor connected to a d.c. supply.  The circuit as shown represents the charging of the capacitor.

(1) One reading you can take for both charging and discharging is time (which you do with a stopwatch).  What one other reading can you take while the capacitor is charging?

(2) Explain why reactance is not a relevant quantity in this question.

(3) Define the time constant for the charge of the capacitor.  Work out the time constant. 

(4) Sketch the graph of voltage against time for the charge of the capacitor.

 

The capacitor is now discharged through the 22 kW resistor

(5) Calculate the time constant for the discharge.

(6) Calculate the current at the start of the discharge.

(7) Calculate the current after 30 s of the discharge.

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