A magnetic field exists around a current-carrying conductor - Leaving Cert Physics - Question 9 - 2014

A compass indicates the direction of a magnetic field through its needle, which is a small magnet. The needle aligns itself with the magnetic field lines, pointing from the magnetic north to the south, thus revealing the direction of the field.

To demonstrate the magnetic field around a current-carrying conductor, set up a circuit using a power supply, battery, and a switch. Place a compass around the wire and close the circuit. Observe that the compass needle deflects, indicating the presence of a magnetic field.

Sketch: Draw a straight wire with current flowing vertically, and surround it with circular field lines, indicating the direction of the magnetic field using arrows.

Draw a bar magnet with labeled ends 'N' (North) and 'S' (South). Illustrate field lines emanating from the North pole and curving around to return to the South pole, ensuring the correct direction of the magnetic field lines is indicated.

When the magnet is moved towards the coil, the needle of the galvanometer deflects, indicating induced current in the coil. This shows that a changing magnetic field generates an electromotive force (EMF).

When the magnet is stationary near the coil, the needle of the galvanometer does not move, indicating no current is induced. This is because a static magnetic field does not generate EMF.

The movement of the magnet changes the magnetic flux through the coil, inducing a current according to Faraday's law of electromagnetic induction. In contrast, no current is induced when the magnet is stationary since there is no change in flux.

Increasing the speed of movement of the magnet towards the coil would result in a greater deflection of the galvanometer needle, indicating a stronger induced current. This occurs because a faster change in magnetic flux generates a higher EMF.