Question

In the given fig. the work done by battery after the switch S is closed–

• A. 100 mJ
• B. – 100 mJ
• C. 80 mJ
• D. – 80 mJ

Answer 1

Answer: (C)

80 mJ

Answer 2

Before the switch S is closed

Q_i = C_eq V

= 5 × 4 = 20 mC

When the switch S is closed

Q_f = CV

= 10 × 4 = 40 mC

W(cell) = DQE = (Q_f – Q_i) × E

= 20 × 4 = 80 mJ