Chapter 3 - Motor Torque & Back E.M.F

Question 1

Explain the term Back e.m.f?

Answer 1

• As the armature windings rotate cutting through the magnetic field,
• this induces a voltage in the armature windings which opposes the applied voltage.
• this is what Lenz’s Law Explains

Eb ∝ ΦN

Question 2

State the factors on which back e.m.f depends?

Answer 2

Factor for Back e.m.f

                                                                                1. Strength of magnetic field - Φ 2. Speed of conductor - N

Eb ∝ ΦN

Question 3

State the torque equation

Answer 3

Torque ∝ ΦIa

The Magnetic Field Strength (Φ)

x

Magnatude of the Armature Current (Ia)