# 6 Magnetism – Part A “Units”

### Syllabus Aims…

6.1 use the following units: ampere (A), volt (V), watt (W),

+ Tesla (T) as an extension! (iGCSE don’t require the unit but it is much harder to teach about Magnetic fields without any Maths or formulae bits!

### Resources…

Use this PowerPoint for the symbols and definitions…  6A Magnetism Units

A physical quantity is something that can be measured. For any measurement, the unit being used must be stated to give an understanding of the scale of the measurement.

For example, distance can be measured in kilometres or in miles. They are similar, but not the same and it is important to identify which was used for the measurement, to know how far the distance actually is.

The units that scientists use all over the world are standardised in the Système Internationale d’Unités – SI units. It is important to remember these six fundamental (or ‘base’) units of measurement:

• metre (m) – unit of length
• kilograms (kg) – unit of mass
• second (s) – unit of time
• ampere (A) – unit of electrical current
• kelvin (K) – unit of temperature
• mole (mol) – unit of the amount of substance

There are many quantities scientists measure that come from the base units.

These derived units are very useful to quote as measurements, but they are not fundamental as they come from fundamental units.

The standard unit for electrical current is the ampere, A.

However, but this comes from the fundamental units of “coulombs” per “second”.

Similar to the watt which is “Joules” per “coulomb”.

Magnetic fields are produced by moving electric charges due to their tiny bit of magnetism inside. We can count how many field lines are produced from a solenoid or magnet and this is where the Tesla is a derived unit based on number of lines in an area.

The current (I) in a wire produces a magnetic field around it. “B” is the symbol for magnetism used in formulae and the unit is the Tesla (T). We don’t tend to use it much in iGCSE Physics but all other specs use this and it helps to know it.

Magnetic fields and electric fields are interrelated and are both components of the electromagnetic force, one of the four fundamental forces of nature. (AS Physics)

Magnetic Flux Density (T):  the number of magnetic lines of flux that pass through a certain point on a surface. The SI unit is T (tesla). It tells us how strong a magnetic field is.