In series motor, torque is proportional to (before saturation)

Option 1: Ia

Option 2: Ia²

Option 3: 1/Ia

Option 4: 1/Ia²

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Correct Option: 2

Explanation

In series motor ϕ ∝ Ia. Therefore T ∝ ϕIa = Ia×Ia = Ia². Hence torque rises very rapidly with current giving high starting torque.