(a) According to the question,
When In parallel
1 / R = 1 / 3 + 1 / 6
1 / R = 1 / 2
R = 2 ohm
If
r = 3 W
ε = 15 V
ε = I (R + r)
15 = I (2 + 3)
I = 3 A
(b) Now find V
R = 2 ohm
Using ohm’s law
V = IR
V = 3 × 2
V = 6 V
(c) V = 6 V
R = 3 ohm
I = V / R
I = 6 / 3
I = 2 A
(d) R = 6 ohm
V = 6 V
I = V / R
I = 6 / 6
I = 1 A