Summary
Highlights
In 1820, Hans Christian Oersted demonstrated that an electric current could move a compass needle, revealing a fundamental link between electricity and magnetism. This discovery profoundly changed physics and underpins much of modern technology, including hydroelectric dams and smartphones. It also explains Earth's magnetic field, which protects us from cosmic radiation.
Magnets have north and south poles, with like poles repelling and opposite poles attracting. Only certain materials, like iron, can be magnets. Earth has its own magnetic field, allowing compasses to work. Magnetic field lines are used to represent magnetic fields, pointing from north to south, similar to electric field lines. Unlike electric fields, magnetic poles cannot be isolated; cutting a magnet in half results in two smaller magnets, each with both poles. Magnetic fields are measured in Teslas.
Oersted's experiment showed that an electric current produces a magnetic field around the wire. Magnetic field lines around a straight current form concentric circles. The first right-hand rule helps determine the direction of this magnetic field: point your thumb in the direction of the current, and your curled fingers indicate the direction of the magnetic field lines.
A magnet also exerts a force on a current running through a wire. This force is perpendicular to both the magnetic field and the current. The second right-hand rule helps determine this direction: point your arm in the direction of the current, bend your fingers to represent the magnetic field, and your thumb points in the direction of the force. The magnitude of this force is given by the equation F = I l B sinθ, where I is current, l is wire length, B is magnetic field strength, and θ is the angle between the current and the magnetic field.
Earth's magnetic field protects us from solar radiation by deflecting charged particles. A magnetic field exerts a force on single electric charges moving through it. The equation for this force is F = q v B sinθ, where q is the charge, v is its velocity, B is the magnetic field strength, and θ is the angle between the velocity and the magnetic field. The third right-hand rule helps determine the force's direction: point your arm in the direction of the particle's velocity, bend your fingers to the magnetic field, and your thumb indicates the force direction for a positive charge (opposite for negative).