CBSE Class 10 Physics Magnetic Effects of Electric Current Notes Set 02

Magnets and Fields

Every magnet has a north and a south pole. Like poles repel and unlike poles attract. Field lines leave the north pole and enter the south pole. A freely suspended magnet points north-south, and breaking a magnet gives two smaller magnets. Heating strongly destroys magnetism. Soft iron gives temporary electromagnets and steel gives permanent magnets.

Current and Magnetism

Oersted found that a current-carrying wire deflects a compass needle, so a current produces a magnetic field. Electromagnets and electric bells use this.
Fleming's left-hand rule gives the direction of the force on a current-carrying conductor in a magnetic field (the motor rule). Fleming's right-hand rule gives the direction of induced current (the dynamo rule).

Induction and Machines

When a conductor cuts magnetic field lines, an EMF is induced, and it grows with the rate of cutting. A dynamo uses a rotating coil: commutator and brushes give direct current, while slip rings give alternating current.
A transformer steps an AC voltage up or down. A step-up transformer has more turns in the secondary than in the primary. AC is used for transmission because it is easy to step up and down with little loss.

Earth's Magnetism

The earth acts like a huge bar magnet, with its magnetic pole in the north lying near the geographical north. Its elements are declination, dip and the horizontal component.