A 240 V dc series motor takes 40 A when giving its rated

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A 240 V dc series motor takes 40 A when giving its rated output at 1500 rpm. Its resistance is 0.3 ohms. The value of resistance which must be added to obtain rated torque at 1000 rpm is _______ ohms

1. 1.9 ohms
2. 19 ohms
3. 4.2 ohms
4. None of the above

Correct Option: A

E_b2 = E_b1 ×	1	×	N₂	= 152 V
	N₁		Ia₁

I _a1 = I _a2 = 40 Ω
R_ext = 2.2 – 0.3 = 1.9 Ω