**Concept**:

__Back emf:__

- In dc motor also generator action takes place.
- Because of this generator action the rotating conductor's cuts the flux and emf induced in the conductors.
- This induced emf is called back emf. It always opposes the supply voltage.

The back emf induced in the dc motor can be given by,

Eb = (ϕZNP) / (60 A)

Where,

ϕ = flux/pole

Z = total number of conductors

A = number of parallel paths

N = speed in RPM

P = number of poles

**Calculation**:

\(E = \frac{{\phi ZNp}}{{60A}} = \frac{{0.01 \times 666 \times 4 \times 1000}}{{60 \times 2}} = 222 V\)

I_{a} = (V - E) / R_{a} = (230 - 222) / 0.267

I_{a} = 29.96 A

Internal power ( P_{d}) \(= \;EI_a = 222\; \times \;29.96 = 6651.685 Watt\)

Shaft Power output,

P_{out} = P_{d }- Rotational losses

\(\begin{array}{l} {P_{out}} = 6651.685\;-\;600\; = 6051.685\\ T = \frac{{{P_{out}}}}{\omega } = \frac{{6051.685}}{{2\pi \times \frac{{1000}}{{60}}}} = 57.78\;Nm \end{array}\)