Measuring the strength of a magnetic field
Physics Narrative for 11-14
Find out how to measure the strength of a magnetic field
For quantitative work, the fact that a magnet will cause a force to act on a current-carrying wire is used to measure the strength of the magnetic field. If there is a direct current in a wire, a nearby magnet will cause a force to be exerted between the magnet and the wire. If the direction of the magnetic field is at a right angle to that of the current, and the length of the wire is 1 metre, carrying a current of 1 ampere, then a force of 1 newton will act on the wire when the magnetic field strength is equal to 1 tesla, 1 T. So the strength of a magnetic field is measured in units of tesla (T). Nikola Tesla was a Yugoslav Serb physicist (1856–1943).
A magnetic field of 1 tesla (T) is a strong field. The bar magnets found in schools create field strengths of the order of 1 × 10-4 tesla. The Earth's magnetic field near the UK has a strength of about one tenth of this, 1 × 10-5 tesla.