If one put a small compass needle (magnet) in a magnetic field then north will point in the field direction. When you draw the magnetic field lines this means that they always goes from a North pole to a South pole.
Moving charges give rise to a magnetic field.
So a wire with a current will produce a magnetic field.
When a wire with a current is placed in an external field then the field from the current
in the wire combines with the external field to create a force on the wire. The force is
perpendicular to both the field direction and the current (wire) direction.
Look at the data booklet:
F = B•I•L
Where B is the magnetic flux density in Tesla, I is the current in Amperes and L is the length of the
wire in meters and F is the force in Newtons.
If the field is not perpendicular to the current but there is an angle θ between the current and
the field then the formula changes to:
F = B•I•L•sin(θ)
Use your right hand. Put your fingers in the field direction and the thumb in the current direction. The force
is the sticking out of the palm of your hand.
When a free charge such as a free electron moves through a magnetic field the electron will experience a force
perpendicular to both the field direction and the direction of the movement.
Look at the data booklet:
F = B•q•v
Where B is the magnetic flux density in Tesla, q is the charge in Coulomb and v is the velocity in m/s
and F is the force in Newtons.
If the field is not perpendicular to the velocity but there is and angle θ between the velocity and
the field then the formula changes to:
F = B•q•v•sin(θ)
Use your right hand. Put your fingers in the field direction and the thumb in the current direction. The force
is the sticking out of the palm of your hand. However, remember that electrons that move create a current
in the opposite direction of their movements. So another way of doing it is to now use your left hand and let
the thumb be in the direction of the electron movement.
The magnetic flux density (B) gives the strength and direction of a magnetic field. It is a vector quantity.
It has the unit Tesla (T).
