Laws and rules G001B

Solve problems in electromagnetic circuits

Right-hand thumb rule (straight conductor)

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• Grasp the conductor in the right hand with the thumb pointing in the direction of current flow.

• The fingers point in the direction in which the magnetic force is acting.

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Right-hand thumb rule (Solenoid)

• Grasp the solenoid in the right hand so that the fingers point in the direction of current flowing through the coil.

• Extend the thumb at right angles to these fingers and the thumb will point in the direction of the north pole.

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Mangnetmotive Force (mmf)

• mmf = I.N in amp-turns• The value of mmf is

determined by the number of turns in a coil and the amount of current flowing. To adjust the amount of mmf the current is adjusted.

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Faraday’s law of induced e.m.f.

• The value of the e.m.f. induced in a circuit depends on the number of conductors in the circuit and the rate of change of the magnetic flux linking the conductors.

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Fleming’s right-hand rule (Generator)

• Place the thumb, index finger and middle finger of the right hand at right angles [90°] to each other– Point the thumb to indicate the

direction of motion of conductor through the flux

– Point the first finger to indicate the direction of magnetic flux action

– The middle finger will then point in the direction in which the induced e.m.f. acts along the conductor

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Fleming’s left-hand rule (Motor)

• Place the thumb, index finger and middle finger of the left hand at right angles [90°] to each other– Point the first finger to indicate

the direction of magnetic flux action.

– Point the middle finger in the direction of current flow in the conductor.

– The thumb now indicates the direction in which the force is exerted on the conductor.

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Lenz’s Law

• The direction of an induced e.m.f. is such that the resulting current flow will produce a magnetic field which tends to oppose the original motion causing the induced e.m.f.