Skip to main content

The National MagLab is funded by the National Science Foundation and the State of Florida.

Magnetic Field of a Solenoid

One can create a stronger, more concentrated magnetic field by taking wire and forming it into a cylindrical coil, called a solenoid.

Generally, magnetic fields can be produced by electric currents. A wire that has electrical current running though it is surrounded by a small magnetic field. Those fields are so minuscule that we don’t really notice them.

The strength of the magnetic field can be increased by taking the wire and forming it into a coil. The field around the wire becomes more concentrated and is stronger inside the loops of the coil than outside it. By adding more loops to a coil, you create an increasingly strong magnetic field.

The tutorial below shows what happens when a magnetic field forms around a solenoid that is surrounded by iron fillings.


  1. Find the key parts of the demo: Solenoid, battery, knife switch, and iron filings.
  2. Click the Power button to lower the knife switch and close the electric circuit.
  3. Watch the iron fillings react to being in a magnetic field.
  4. Hide magnetic field lines and observe the way the fillings have positioned themselves.

When the copper solenoid is connected to a battery, it becomes an electromagnet. The ferromagnetic iron filings allow us to physically see the otherwise invisible magnetic fields that surround us every time current travels through a coil of wire.