How is the braking torque generated in an electromagnetic retarder?

• A. By an electromagnetic field created by powering coils, which inhibits rotor rotation.
• B. By hydraulic pressure on brake pads.
• C. By mechanical friction of a clutch.
• D. By air resistance.

Answer: (A)

An electromagnetic retarder generates braking torque by using coils to create a magnetic field. As the rotor (a conductor) moves through that magnetic field, eddy currents are induced in the rotor. These currents produce their own magnetic fields that oppose the motion, producing a drag torque that slows the rotor. The energy of the moving vehicle is converted into heat in the retarder’s magnetic circuit rather than in friction pads or the surrounding air.

This is why the correct description is the electromagnetic field created by powering coils, which inhibits rotor rotation. The other options describe hydraulic braking, mechanical clutch friction, or air resistance, none of which explain how an electromagnetic retarder actually generates torque.