Electromagnets Investigation

PLANNING

SCIENTFIC THEORY:

Electromagnets

An electromagnet is a device consisting of a solenoid usually a cylindrical coil of insulated wire in which an iron core is placed. An electric current passed through the coil induces a strong magnetic field along the axis of the helix. When the iron core is placed in this field, microscopic domains that can be considered small permanent magnets in the iron align themselves in the direction of the field, thus increasing greatly the strength of the magnetic field produced by the solenoid. The magnetization of the core reaches saturation once all the domains are completely aligned, and an increase of the current in the solenoid has little further effect. When the current is switched off, the core retains only a weak residual magnetism.

The Domain Theory

The domain theory of magnetism suggests that a magnetic material such as iron contains within its structure tiny cells called domains and that mini molecular magnet exist inside theses domains.

In an unmagnetised piece of iron all the mini magnets within a particular domain point in the same direction but in each neighbouring domain they point in different directions. The result of this is that the magnetised effect of the domains cancel each other out.

In an unmagnetised piece of iron all the domains are lined up so that their magnetic effect reinforce each other.

Flemming’s left hand rule

Using Flemming’s left hand rule the direction of the force/motion can be predicted

Electromagnet induction

If a conductor such as a piece of wire is moved through a magnetic field cutting magnetic lines of force a voltage or emf will be induced across its ends. The process which produces the emf is called electromagnetic induction. If the wire is part of a complete circuit the induced emf will cause a current to flow.