Question

The potential across a generator is 125V when it is delivering 10A. When it delivers 30A the potential is 120V. What are the resistance of armature and induced e.m.f. ?

• A. $5\Omega,127.5V$
• B. $0.25\Omega,127.5V$
• C. $2.5\Omega,120V$
• D. $5\Omega,130V$

Answer 1

Answer: (B)

$0.25\Omega,127.5V$

Answer 2

Using V = E - $ir$ , we get, 125 = E - 10r ....$(i)$ and 120 = E - 30r ...$(ii)$ Subtracting $(ii)$ from $(i)$, 5 = 20$r$ or $r$ = 0.25$\Omega$ from $(i)$ 125 = E - (10 $\times$ 0.25) or E = 125 + 2.5 = 127.5 V