Question

A simple electric motor has an armature resistance of $1 \,\Omega$ and runs from a d.c. source of $12 \,V$. It draws a current of $2 \,A$ when unloaded. When a certain load is connected to it, its speed reduces by $10 \%$ of its initial value. The current drawn by the loaded motor is

• A. 3 A
• B. 6 A
• C. 2 A
• D. 1 A

Answer 1

Answer: (A)

We know that back emf $=V−IR$
$\Rightarrow $ back emf $=12-2(1)$
$\Rightarrow $ back emf $=12-2=10 V$
$\Rightarrow 10 \%$ of this emf $=0.1 \times 10=1 V$
$\Rightarrow $ Hence the current $=1 \times 1=1 A$
hence the current drawn by loaded motor is $2+1=3 A$