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UNIT 22: FORCE ON CONDUCTOR IN A MAGNETIC FIELD

• When two different magnetic fields (for example from a solenoid and a permanent magnet) interact with one another, a force is experienced from a region of stronger magnetic field to a region of weaker magnetic field.

• Left-hand Rule: Directions of current, magnetic field and force are all perpendicular to each other.

• Two parallel wires with current in same direction are attracted to each other.

• Two parallel wires with current in opposite directions are repelled from each other.

• Working of loudspeaker

• Cone produces compressions and rarefactions in the air because it vibrates with the coil.

• The coil vibrates because

• Current in coil produces magnetic field

• Poles of coil are reversed when the current changes direction

• The coil experiences attraction and repulsion from the N (or S)-pole of permanent magnet.

• Working of D.C. Motor

• When current flows through coil, it becomes a magnet.

• Its magnetic field interacts with the magnetic field of the permanent magnet. Hence it experiences forces.

• To keep the coil rotating, the forces need to be reversed after every half turn. Therefore,
split-ring commutator reverses the direction of current after every half turn.