Question

The current drawn by a 220 V DC motor of armature resistance 0.5 Ω and back emf 180 V is _______.
1. 0.8 A
2. 80 A
3. 8 A
4. 18 A

Answer 1

Correct Answer - Option 2 : 80 A

Concept:

In a DC shunt generator, generated emf is given by

Eg = Vt + IaRa

In a DC shunt motor, back emf is given by

Eb = V – IaRa

Where, Ia is armature current

Ra is armature resistance

Calculation:

Armature resistance (Ra) = 0.5 ohm

Voltage (V) = 220 V

Back emf (Eb) = 180 V

Eb = V – IaRa

⇒ 180 = 220 – Ia(0.5)

⇒ Ia = 80 A