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5.86: Solenoid

Difficulty Level: At Grade Created by: CK-12

Splat! This paintball player took a direct hit! Did you ever play this extreme game? The trigger on a paintball gun is electronic and uses a device called a solenoid.

What Is a Solenoid?

A solenoid is a coil of wire with electric current flowing through it. You can see a solenoid in the Figure below. Current flowing through the coil produces a magnetic field that has north and south poles. You can see an actual solenoid with a compass showing its magnetic north pole at this URL: http://www.youtube.com/watch?v=AgZHqfIBkUI.

Schematic of a solenoid

Q: How is a solenoid like a bar magnet?

A: Like a bar magnet, a solenoid has north and south magnetic poles and is surrounded by a magnetic field.

Strength of a Solenoid

Any wire with current flowing through it has a magnetic field. However, the magnetic field around a coiled wire is stronger than the magnetic field around a straight wire. That’s because each turn of the wire in the coil has its own magnetic field. Adding more turns to the coil of wire increases the strength of the field. Increasing the amount of current flowing through the coil also increases the strength of the magnetic field.

Uses of Solenoids

A solenoid is generally used to convert electromagnetic energy into motion. Solenoids are often used in devices that need a sudden burst of power to move a specific part. In addition to paintball markers, you can find solenoids in machines ranging from motor vehicles to electric dishwashers. Another device that uses solenoids is pictured in the Figure below.

Pinball machines contain multiple solenoids that operate bumpers, switches, and other moving parts

This pinball machine uses several solenoids to operate bumpers, switches, and other moving parts.


  • A solenoid is a coil of wire with electric current flowing through it, giving it north and south magnetic poles and a magnetic field.
  • Using more turns of wire in the coil or more current increases the strength of the solenoid’s magnetic field.
  • A solenoid converts electromagnetic energy into motion, providing a burst of power that can move a specific part of a device.

Explore More

At the following URL, explore the solenoid animation. Try varying the voltage and the direction of the current. Observe how these changes affect the magnetic field. Write a paragraph to summarize your observations. http://www.physics-chemistry-interactive-flash-animation.com/electricity_electromagnetism_interactive/solenoid_magnetic_field_current_poles_north_south.htm


  1. Describe a solenoid and its magnetic field.
  2. Which solenoid pictured below has a stronger magnetic field? How do you know?

  1. How are solenoids used?




Coil of wire with electric current flowing through it, giving it a magnetic field like a bar magnet.

Image Attributions


Difficulty Level:

At Grade

Concept Nodes:


7 , 8

Date Created:

Nov 01, 2012

Last Modified:

Oct 02, 2015

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