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Capacitor Questions

Q3. In the circuit below the capacitor is charged to a potential difference of 6.0 V.

When the switch is moved from A to B , the capacitor discharges through the resistor.

a)   Show that the initial value of the discharge current is about 1 mA.

Initially, the capacitor provides a potential difference of 6V across the resistor R. Using Ohm's Law we can calculate the current that would run at that point in time.

I = V/R

= (6/ 5.6 x 10 3 )

= 1.1 x 10 -3 A

= (about) 1 mA

(2 Marks)

b)   The time constant RC of the discharge circuit is about 26s.

Calculate the current in the discharge circuit after the switch has been closed for a time equal to RC.

 

I = I 0  e –t/RC

I = 1.1 x 10 -3 x e -1  

I = 1.1 x 10 -3 x 0.37

I = 0.41 mA

(2 Marks)

(Total 4 marks)