Magnetic Effects of Electric Current Practice

A motor converts electrical energy into mechanical energy (electricity in → rotation out) and uses Fleming's left-hand rule. A generator converts mechanical energy into electrical energy (rotation in → electricity out) and uses Fleming's right-hand rule. Motor has a split-ring commutator; AC generator has slip rings.

The commutator consists of two half-cylinders of copper separated by insulation — forming two 'split rings'. As the coil rotates, the brushes slide from one half-ring to the other every half turn, reversing the direction of current supplied to the external circuit. This is why it is called a split-ring commutator — it is literally a ring split into two halves.

Electromagnetic induction occurs only when there is a change in magnetic flux. When the magnet is stationary inside the coil, the flux is constant (not changing), so no EMF is induced and no current flows. The galvanometer shows zero deflection. Moving the magnet — whether in or out — changes the flux and induces a current.

A standard DC motor is designed for direct current. If AC is supplied, the current reverses direction rapidly (50 times per second in India), which would cause the force on the coil to reverse 50 times per second. This would not produce smooth rotation. Universal motors (used in mixers, grinders) are designed to work on both AC and DC. Standard DC motors require DC supply.

The live wire is at 230 V potential (high potential). If a person standing on the ground touches the live wire, current flows from the live wire, through the person's body, to the earth (ground, which is at zero potential). This gives a serious electric shock. The neutral wire is at zero potential (same as earth), so touching it alone does not normally cause a shock — there is no potential difference between the neutral wire and the earth.

According to Lenz's law, the induced current will flow in a direction such that it opposes the increase in flux. So the induced current creates its own magnetic field that opposes the original increasing flux. Lenz's law is a consequence of conservation of energy — if the induced current aided the increase in flux, it would perpetually amplify itself without any energy input, which is impossible.