Magnetic Force: History, Properties, and Key Experiments

Understanding Magnetic Force

The fundamental principle behind all magnetic phenomena is that a force arises between electric charges when they are in motion. This force is known as magnetic force.

Key Discoveries and Experiments

Oersted's Discovery (1820)

In 1820, Hans Christian Oersted accidentally discovered that an electric current could produce a magnetic field, deflecting the needle of a compass.

Faraday's Power Line (1831)

Michael Faraday's concept of the 'power line' explained the behavior of forces acting at a distance.

Properties of Magnetic Field Lines

The properties of magnetic field lines are:

1. All magnetic field lines run from the north to the south magnetic pole.
2. The magnetic field strength is directly proportional to the number of field lines per unit area.
3. Field lines never intersect or cross.
4. They are closed, with no disruption on the surface of the magnet.
5. The magnetic field vector (B) is tangent to the field line that passes through a specific point on a line of force.

Absence of Magnetic Monopoles

Pierre de Maricourt verified that magnetic monopoles do not exist.

Ampère's Contributions

André-Marie Ampère discovered that two wires carrying electric current can attract or repel each other, similar to magnets. He explained natural magnetism by assuming that electric current acted at a molecular level.

Faraday's Field Theories

Michael Faraday developed field theories that could generate electrical currents from variable electric fields.

Maxwell's Field Development (1860)

James Clerk Maxwell further developed field theories and concluded that magnetic fields can be created from varying electric fields.

Lorentz Force

The Lorentz force is the diversionary force experienced by an electrically charged particle as it enters a region with a homogeneous magnetic field (a field with the same intensity at all points).

Thomson's Experiment (1897)

In 1897, Joseph John (JJ) Thomson, using a cathode ray tube, experimentally determined the ratio between the charge and mass of the electron (q/m), also known as the specific charge of the electron.

Interaction of Current-Carrying Conductors

When two current-carrying electrical conductors are spaced apart, they experience an attractive or repulsive force due to the interaction between the magnetic fields generated by the currents.

Oersted's Experiment in Detail

In 1820, while working in his lab, Oersted set up an electrical circuit and placed it near a magnetic needle. Without current in the circuit (open circuit), the magnetic needle oriented itself in the North-South direction, as expected. The setup was similar to Figure 4. A branch of the circuit was placed parallel to the needle, also directed in the North-South direction. When Oersted established a current in the circuit, he observed that the magnetic needle deflected, tending to orient itself perpendicular to the conductor. Upon interrupting the current flow, the needle returned to its original position in the North-South direction.

These observations demonstrated that an electric current could act like a magnet, causing deviations in a magnetic needle. This was the first indication of a close relationship between electricity and magnetism: an electric current can produce magnetic effects.