Mar 2021

Electromagnetism: The Magnetic Field Strength Of A Solenoid

March 19, 2021

Physics Tuition, Physics Tuition Singapore

Electromagnetism is a branch of study concerned with the interactions between electrically charged particles, namely, due to electromagnetic force. Electromagnetic force is carried along electric fields and magnetic fields.

For example, when an electric current flows through a wire, it creates a magnetic field that surrounds the wire in circles. The more current that flows through, the stronger the magnetic field will become. The direction of the magnetic lines and force can be determined by using Fleming’s Right-hand Rule, which surely you’ve learn in school or at physics tuition already!


When you coil up a wire into a spring-like shape, it forms an electromagnet called a solenoid. Coiling it into this helical structure concentrates and increases the magnetic field. This is because of the additive effect from each turn of the wire.

When an electric current is passed through the wire, the solenoid behaves like a magnet with north and south poles at the two ends. The magnetic field of a solenoid can draw in or push out a permanent magnet. This action is useful in creating electrical switches.

A solenoid can also be used to create an electromagnet. Placing an iron rod inside a solenoid permanently can increase the magnetic effect greatly.

Effect of Ferrous Cores

While all electromagnets consist of a current carrying conductor, the strength of the generated magnetic field depends on the surroundings. As air is not very good at carrying a magnetic field, the field around the wire is quite weak. By inserting a core within a coil, the power of the magnetic field can be increased. When you put a ferrous (iron) core inside a solenoid, the magnetic field lines are concentrated and therefore strengthen the magnetic field.

Before and after you place a ferrous core

Magnetic flux

The magnetic flux is defined as the number of magnetic field lines that pass through a given area. The area can be of any scale and under any orientation relative to the direction of the magnetic field. It is a helpful tool for explaining the effects of the magnetic force on something that occupies a given area.

Uses of electromagnetism

Electromagnetism is commonly used in devices such as doorbells, electric motors, and loudspeakers. Another important application of electromagnetism is magnetic resonance imaging (MRI) that doctors use to detect diseases or injuries. There are so many things in our daily lives that use electromagnetism!

You might be wondering, why do we use an electromagnet instead of a permanent magnet? There are two main advantages of using an electromagnet. Firstly, they can be switched on and off. Secondly, the magnetic field strengths can simply be controlled by changing the amount of current, increasing the number of coils of wire, or placing a magnetic material instead the solenoid coil. This is something you cannot do with a regular magnet.


Electromagnetism is a basic working principle for many of the appliances we use at home and in the world. Need to brush up on your electromagnetism knowledge for the A levels? We provide H2 Physics tuition to help you sharpen your physics skills for the exams! For those still in secondary school, our O level physics tuition can also assist you to improve your physics grades!

WhatsApp chat