Electromagnetism
Induction of a magnetic field
When current passes through a conductor, a magnetic field is induced around the wire.
Magnetic effect is only present when there is a change in current.
Right hand rule – for straight conductor
Use your thumb and point either INTO/OUT the page.
Fingers will curl in direction of field.
Into the page X
Out the page
Right hand rule for solenoid
Always point thumb in direction of north.
See if wires go over the top & down the back OR down the back and over the front.
Fleming’s Left-hand rule (at right angles)
Point finger = N S
Zap finger = into/out page
Thumb = thrust/force – direction of conventional current
NB! For electrons we reverse the current direction!!
Factors affecting force on straight current-carrying conductors
Magnitude of magnetic field
Size of current
Length of conductor in the magnetic field.
Needs to be at right angles for maximum force.
If conductor is parallel force = 0.
F=I l B sin θ
F = force
I = current
l = length of conductor
B = magnetic field.
θ = angle between conductor and magnetic field.
Direct current motor (DC)
Motor converts electrical energy to mechanical energy.
Look at which direction current is flowing.
Each side of moto will experience different force.
How it works
Current flows through the coil windings (armature) in a magnetic field.
It will experience a turning force (torque.)
Coil can only rotate continually in one direction if the direction of the current is
reversed for each half turn of the coil.
Split ring commutator reverses the direction of the current in the coil windings every
half turn.
Induction of a magnetic field
When current passes through a conductor, a magnetic field is induced around the wire.
Magnetic effect is only present when there is a change in current.
Right hand rule – for straight conductor
Use your thumb and point either INTO/OUT the page.
Fingers will curl in direction of field.
Into the page X
Out the page
Right hand rule for solenoid
Always point thumb in direction of north.
See if wires go over the top & down the back OR down the back and over the front.
Fleming’s Left-hand rule (at right angles)
Point finger = N S
Zap finger = into/out page
Thumb = thrust/force – direction of conventional current
NB! For electrons we reverse the current direction!!
Factors affecting force on straight current-carrying conductors
Magnitude of magnetic field
Size of current
Length of conductor in the magnetic field.
Needs to be at right angles for maximum force.
If conductor is parallel force = 0.
F=I l B sin θ
F = force
I = current
l = length of conductor
B = magnetic field.
θ = angle between conductor and magnetic field.
Direct current motor (DC)
Motor converts electrical energy to mechanical energy.
Look at which direction current is flowing.
Each side of moto will experience different force.
How it works
Current flows through the coil windings (armature) in a magnetic field.
It will experience a turning force (torque.)
Coil can only rotate continually in one direction if the direction of the current is
reversed for each half turn of the coil.
Split ring commutator reverses the direction of the current in the coil windings every
half turn.
