Step 1:

The function is .

From the definition of current : .

.

The current at time is .

Step 2:

(a)

Find the current at .

.

(b)

Find the current at .

.

Step 3:

Apply derivative on each side with respect to .

To find the lowest current value, set .

.

The current will be lowest at .

Solution :

The current at time is .

(a) .

(b) .

The current will be lowest at .