How to Calculate the Force in a Solenoid

Written by douglas quaid
  • Share
  • Tweet
  • Share
  • Pin
  • Email
How to Calculate the Force in a Solenoid
A solenoid is made from a coil of wire, like this inductor. (drosselspule, induction coil image by Sascha Zlatkov from Fotolia.com)

A solenoid is an electromagnet made by passing current through a coiled wire. If there is a metal core in the centre of the loop, the magnetic field can exert a force on it which causes it to move forwards or backwards through the loop, depending on the polarity of the magnetic field. Solenoids have a huge variety of applications. The starter relay in your car is a solenoid that uses a small current from the battery to move a switch, which relays the large current needed to start the engine.

Skill level:
Easy

Other People Are Reading

Instructions

  1. 1

    Determine the magnetic permeability of the core of the solenoid. The core is the material in the centre of the loop. Most materials, including air, have a permeability that's close to the magnetic constant, μ = 4π x 10^-7. Ferromagnetic materials such as nickel or magnetic iron have higher permeability. Magnetic iron, for example, has a permeability of 200.

  2. 2

    Calculate the strength of the magnetic field at the centre of the solenoid. The strength of the magnetic field is given by the equation B = knI, where:

    B = magnetic field in units of Tesla

    k = the magnetic permeability of the core, as determined in Step 1

    n = turn density = number of turns / length of solenoid (in meters)

    I = current in solenoid (in amperes)

  3. 3

    Calculate the force exerted with the equation F = qvB.

    F = force in Newtons

    q = charge of point particle in coulombs

    v = velocity of point particle

    B = magnetic field strength calculated in Step 1

    Both v and B are vectors, amounts that have both a magnitude and direction. To understand vectors, consider the difference between position and velocity. Position has no direction, it just indicates where you are. Velocity, however, is a vector that considers both your speed and the direction you're travelling in.

    The above equation is valid when vectors v and B are perpendicular. In this case, force, F, is a vector that is perpendicular to both v and B. However, when v and B are not perpendicular, the equation is:

    F = qvB x sinθ, where θ (theta) is the angle between v and B, and is less than 180 degrees.

Don't Miss

Filter:
  • All types
  • Articles
  • Slideshows
  • Videos
Sort:
  • Most relevant
  • Most popular
  • Most recent

No articles available

No slideshows available

No videos available

By using the eHow.co.uk site, you consent to the use of cookies. For more information, please see our Cookie policy.