Disconnect the dc voltmeter from the Permanent Magnet DC Motor. In this section,

Question

Disconnect the dc voltmeter from the Permanent Magnet DC Motor. In this section, you will observe the opposition to rotation of the Permanent Magnet DC Motor when the terminals of the motor are not short-circuited and when they are. Make the shaft of the Permanent Magnet DC Motor rotate with your hands. Notice that it is easy to make the motor shaft rotate. Explain why. Short-circuit the two terminals of the Permanent Magnet DC Motor with a lead. Make the motor shaft rotate clockwise with your hands, then make it rotate counter-clockwise. Notice that it is less easy to make the motor shaft rotate when the motor terminals are short-circuited. Explain why.

Explanation / Answer

The main concept is about Lenz law. That iseffect opposes

The cause.   

So when terminals are open circuited there is no current.

Actually when we rotate shaft end generated and current will flow if of load is present . That current will create motoring force which opposes our hand. More load more opposes

So open circuits means no load and short circuit means full load

So under no load no current no motoring effects no Lenz so it is requier less force to rotate the shaft.

So under full load current very high. Motoring effects comes and Lenz comes into action hence very high opposition to roasting shaft.

Hence it is less easy to rotate the shaft of permanent magnet motor . When. Rotated as generator.

Comment any doubt

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