Electric circuits switch

Question

Answer 1

(1)

Step 1:

If the switch is moved to position "B" at t = 0, the capacitor will discharge and a current will flow through the resistor.

Apply Kirchhoff's second law (conservation of energy) we get : .

Write the above equation in the form of charge : .

Find the voltage across capcitor using the above equation.

Integrating on each side.

Initially the capacitor is charged upto .

Now substitute , and .

Solution :

The voltage across capcitor is .

Answer 2

(2)

Step 1:

If the switch is moved to position "B" at t = 0, the capacitor will discharge and a current will flow through the resistor.

Apply Kirchhoff's second law (conservation of energy) we get : .

Substitute   in .

Solution :

The voltage across resistor is .

Answer 3

(3)

Step 1:

Find the current flowing through the circuit.

Since the element are connected in series, the circuit current equals to current flowing through the resistor.

Current flowing through the resistor is .

Substitute and .

Current flowing through the circuit is .

Solution :

Current flowing through the circuit is .