Magnetic field created by a straight wire is very weak
When the wire coils up, this field becomes stronger; the greater the number of coils, the stronger the magnetic field
A solenoid was invented to make them even stronger (basically has a lot of turns)
If an iron core is inserted into a solenoid we make the magnet 1000x stronger and it becomes an electromagnet
Solenoids are so strong because, with each loop the field lines line up with each other resulting in lots of field lines pointing in the same direction and are also very close together. The closer the field lines, the stronger the field is.
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The Motor Effect
When a current-carrying wire is placed withing a magnetic field of a permanent magnet, the wire is pushed at 90 degrees to this field. (Fleming's left-hand rule)
The most relevant use of this effect is making electric motors
Examples of devices that use an electric motor: fan, vacuum cleaner, microwave etc.
If you reverse the magnetic field, the spinning direction will reverse
If you reverse the magnetic field and the current, nothing will change
To increase the spinning of the coil, you need to have stronger currents or magnets
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Permanent and Induced Magnets
Permanent Magnets: magnets which produce their own magnetic field
Induced Magnets: magnetic materials that turn into a magnet when they are put into a magnetic field; they are no longer magnets when they are taken away from the magnetic field
Compasses always point north when they are not near a magnet because the Earth generates its own magnetic field, which shows the core of the Earth must be magnetic
Magnetic materials are: nickel, cobalt and iron. Steel is an alloy of iron so can become a magnet when put into a magnetic field.
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