Final answer:
The back emf developed by a DC motor supplied from a 120 V DC power source drawing 50 A with an armature resistance of 0.1Ω is calculated to be 115 V.
Step-by-step explanation:
To calculate the back emf developed by the motor, we can use the formula for the voltage across the armature (Va), which is equal to the supply voltage (V) minus the voltage drop across the armature resistance (Ir), where 'I' is the current and 'r' is the resistance. So, Va = V - Ir. In this case, the supply voltage (V) is 120 V, the current (I) is 50 A, and the armature resistance (r) is 0.1Ω.
Using the formula:
- Va = 120 V - (50 A × 0.1Ω)
- Va = 120 V - 5 V
- Va = 115 V
Therefore, the back emf developed by the motor is 115 V.