What is a magnetic field?

A magnetic field is a region around a magnet where magnetic forces can be detected.

Magnetic fields are created by moving electric charges, such as those in a current-carrying wire, or by the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property called spin. The strength and direction of a magnetic field are represented by magnetic field lines, which show the path that a north magnetic pole would take if it were free to move. These lines emerge from the north pole of a magnet and enter the south pole, forming closed loops.

In GCSE Physics, you will often encounter magnetic fields in the context of bar magnets and electromagnets. A bar magnet has a permanent magnetic field, while an electromagnet generates a magnetic field when an electric current flows through a coil of wire. The magnetic field around a straight current-carrying wire forms concentric circles, and the direction of the field can be determined using the right-hand rule: if you point the thumb of your right hand in the direction of the current, your fingers will curl in the direction of the magnetic field.

Magnetic fields are measured in units called teslas (T) or gauss (G), with 1 tesla being equal to 10,000 gauss. The Earth's magnetic field, which protects us from solar radiation and helps in navigation, is relatively weak, about 0.00005 teslas.

Understanding magnetic fields is crucial for many applications, including electric motors, generators, and transformers. In these devices, magnetic fields are used to convert electrical energy into mechanical energy and vice versa. Additionally, magnetic fields play a vital role in medical technologies such as MRI (Magnetic Resonance Imaging) scanners, which use strong magnetic fields to produce detailed images of the inside of the human body.