16.0 MAGNETIC EFFECT OF AN ELECTRIC CURRENT

The link between electricity and magnetism is one of the most important discoveries in physics. In 1820, Hans Christian Oersted found that a current-carrying wire deflects a compass needle, showing that electricity can produce magnetism. This chapter explores the magnetic fields around conductors and solenoids, the force on a current-carrying wire in a magnetic field, and the practical applications that have shaped our world, from electric bells to motors.

16.1 OERSTED'S DISCOVERY

16.1.1 The Experiment

Oersted set up a simple circuit with a straight wire and placed a compass needle parallel to the wire. When the circuit was closed and current flowed, he observed that the compass needle deflected and aligned itself perpendicular to the wire. When the current was reversed, the needle deflected in the opposite direction. This was the first evidence that an electric current produces a magnetic field.

16.1.2 Magnetic Field Around a Straight Conductor

• The magnetic field lines form concentric circles around the wire.
• The field is strongest close to the wire and becomes weaker as distance increases.
• The direction of the field (clockwise or anticlockwise) depends on the direction of the current.

Right-Hand Grip Rule (for straight conductor): If you grasp the conductor with your right hand such that the thumb points in the direction of the current, your curled fingers show the direction of the magnetic field lines.

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