Question

The armature of a DC motor has resistance of 0.1 ohm and is connected to a 250 V supply. The generated emf when the motor is taking 60 A will be ____.

• A. 244 V
• B. 250 V
• C. 256 V
• D. 280 V

Hint:

Remember: In a Motor, the generated emf ($E_b$) is always less than the supply voltage because it opposes the flow of current. In a Generator, the generated emf ($E_g$) is always greater than the terminal voltage.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
In a DC motor, the supply voltage ($V$) must overcome the back emf ($E_b$) generated by the motor's rotation and the voltage drop across the internal resistance of the armature.

Step 2: Key Formula or Approach:
The voltage equation for a DC motor is: \[ V = E_b + I_aR_a \] where $V$ is supply voltage, $E_b$ is generated (back) emf, $I_a$ is armature current, and $R_a$ is armature resistance.

Step 3: Detailed Explanation:
Given: $V = 250\text{ V}$, $R_a = 0.1\text{ }\Omega$, and $I_a = 60\text{ A}$. We need to find $E_b$: \[ E_b = V - I_aR_a \] \[ E_b = 250 - (60 \times 0.1) \] \[ E_b = 250 - 6 \] \[ E_b = 244\text{ V} \]

Step 4: Final Answer:
The generated emf is 244 V.