Magnetism and Electromagnetism

Magnetism and Electromagnetism

Key Formulas

• Force = Magnetic Flux Density x Current x Length (Of wire within the field)
• Voltage (secondary) x Current (secondary) = Voltage (primary) x Current (primary)

Magnetic Poles and Fields

There are two magnetic poles, the north and the south. The poles of a magnet are the places which have the styrongest magnetic force. Oppisite poles attract each other - the south pole of one magnet will be attracted to the north pole of another magnet. This means the poles that are the same will repel each other - a south pole will reppel another south pole of a magnet. The area around a magnet where a force can attract or repel anither magnet is called the magnetic field.

There are two types of magnets. Permanent Magnets, these produce their own magnetic field and Induced Magnets that become a magnet when placed within a magnetic field and when removed then lose their magnetism quickly. A permanent magnet always attracts an induced magnet.

The arrows on field lines always run from north to south to show the direction of the force that would act on a north pole placed at that point. The density of field lines represent the flux density and shows the strength of the field at that point. The closer the lines are the higher the flux density is. The higher the flux density is the stronger the field is and therefore the greater the force that would be felt on another magnet within the magnetic field.

How to Plot a Magnetic Field

A magnetic field can be plotted by using a magnetic compass:

• Place the bar magnet on a piece of paper
• Place the compass at one of the poles
• On the paper mark what way the compass needle is facing
• Move the compass so that the tail of the needle is at the point just marked

Electromagnetism and Solenoids

Whenever a current flows in a conducting wire a magnetic field around the wire is produced. The direction of field lines depends on the direction of the current and can be found using the Right Hand Grip Methord:

• Hold the wire in your right hand with your thump pointing in the direction of the current
• The fingers curled around the magnet show the direction that the field lines should be drawn.

The strength of the field relies on the size of the current and the distance from the wire. This can be shown by placing a magnetic compass at different points along the wire andd turning the power on and off.

A solenoid is when a wire is wrapped into a cylindrical coil, by shaping the wire you are able to increase the magnetic field and create a strong uniform field within the solenoid. It increases the strength of the magnetic field because, it concentrates a long piece of wire into a small area and the fact that is all looped in the same direction means that the magnetic field lines are all in the same direction. You…