2. Today’s lesson
• How can we measure the strength of
a magnetic field?
• Upon what factors does the
magnitude of the force on a current-
carrying wire depend?
• How is the direction of the force found
for a current-carrying wire in a
magnetic field?
3. What is magnetism?
Electrostatic repulsion is the
force that stops you falling
through the floor. Normally this
force acts at the nanometre
level.
Magnetism is when the
electrons have been lined up
and work together.
The classical view is to see all
the electrons moved to one end
of the magnet, creating an
unbalance. However this does
not happen
http://www.youtube.com/watch?v=wMFPe-DwULM
4. Magnets and magnetic fields
Important facts
1)Magnetic fields have 2 poles
(North, South).
2) The magnetic metals are iron,
nickel, cobalt.
3)The magnetic field is most
dense at the poles.
4)Magnetic field lines go from the
North to South.
5)The Earth has a magnetic field.
6)Current flowing through a wire
creates a magnetic field.
5. Magnetic Fields
Use the iron filings in the Petri dishes to see
the magnetic field lines of a bar magnet.
Try and see the magnetic field of a wire, you
may have to loop the wire around a pencil
a few times (caution hot!)
Use a heatproof mat
6. How can we measure the
strength of a magnetic field?
• Hall probes varies its output
voltage in response to
changes in magnetic field.
• B is the letter used for the
magnetic field (B-field)
• The tesla (symbol T) is the
SI derived unit of magnetic
field B
Hall probes are used to check
timings of pistons in car.
7. Upon what factors does the magnitude of
the force on a current-carrying wire depend?
