Electro-Magnetism © D Hoult 2008

Magnetic Field Shapes

Magnetic fields are represented by lines called lines of magnetic force or lines of magnetic flux

Magnetic fields are represented by lines called lines of magnetic force or lines of magnetic flux These lines show the direction of the force which would act on a free north magnetic pole placed in the field

Magnetic fields are represented by lines called lines of magnetic force or lines of magnetic flux These lines show the direction of the force which would act on a free north magnetic pole placed in the field However, since free north magnetic poles don’t exist... think of the lines as showing which way a very small compass would point if placed in the field

Magnetic fields are represented by lines called lines of magnetic force or lines of magnetic flux These lines show the direction of the force which would act on a free north magnetic pole placed in the field However, since free north magnetic poles don’t exist... think of the lines as showing which way a very small compass would point if placed n the field The “density” of lines on a diagram indicates the strength of the magnetic field

Field due to a straight current-carrying conductor

Field due to a straight current-carrying conductor

It is found that a compass always points perpendicular to the conductor so we conclude that the lines form circles (or cylinders) round the conductor

To remember the sense of the magnetic field, think about

To remember the sense of the magnetic field, think about opening a bottle of wine.

To remember the sense of the magnetic field, think about opening a bottle of wine.

To remember the sense of the magnetic field, think about opening a bottle of wine. demo...

To remember the sense of the magnetic field, think about opening a bottle of wine.

Field due to a short current-carrying coil of wire

Field due to a short current-carrying coil of wire

Field due to a short current-carrying coil of wire

Field due to a long current-carrying coil of wire (also called a solenoid)

Field due to a long current-carrying coil of wire (also called a solenoid)

Field due to a long current-carrying coil of wire (also called a solenoid)

This field is similar to that of a bar magnet

This field is similar to that of a bar magnet

This field is similar to that of a bar magnet

This field is similar to that of a bar magnet

Current into plane of diagram

Current into plane of diagram Current out of plane of diagram

Fields due to two parallel current-carrying conductors

Fields due to two parallel current-carrying conductors Currents flowing in the same sense

Fields due to two parallel current-carrying conductors Currents flowing in the same sense

Fields due to two parallel current-carrying conductors Currents flowing in the same sense

Fields due to two parallel current-carrying conductors Currents flowing in the same sense

Fields due to two parallel current-carrying conductors Currents flowing in the same sense

Fields due to two parallel current-carrying conductors Currents flowing in the same sense The two conductors attract each other

Currents flowing in opposite sense

Close to the conductors the field is very nearly circular

The field is similar in shape to the field of a

The field is similar in shape to the field of a short coil

The field is similar in shape to the field of a short coil The two conductors repel each other