Question

A fully charged mobile phone with a 12 V battery is good for a 10 minutes talk-time. Assume that, during the talk-time the battery delivers a constant current of 2 A and its voltage drops linearly from 12 V to 10 V as shown in the figure. How much energy does the battery during this talk-time?

• A. 220 J
• B. 12 kJ
• C. 13.2 kJ
• D. 14.4 J

Answer 1

The correct option is C 13.2 kJ

P = VI
Energy = P . t = V . It = (V.t)I
I = 2A (given)
V . t = Area under V - t curve
$V.t=(\frac{1}{2}\times 2\times 600)+(10\times 600)$
= 600 + 6000
V . t = 6600
E = (6600) × 2 = 13200 = 13.2 kJ