physics question

Question

A battery has an internal resistance of 0.30 Ω. The potential difference between its terminals is 1.48 V when a current of 0.20 A is being drawn from it.

a) What is its e.m.f.?

b) What is the power rating of a television receiver that uses 270,000 Joules to operate for 1.5 hours?

Answer 1

(a)

 

E - Ir = V_ab

 

(a and b are connected to the + and - terminals, respectively)

 

V_ab = 1.48 V

 

r = 0.30 Ω

 

I = 0.20 A

 

E = V_ab + Ir = [1.48 + (0.30)(0.20)] V = 1.54 V

 

(b)

 

P = (270,000 J) / (1.5 hours x 3600 seconds/hour)) = 50 J/s = 50 W