Electromagnetic Induction
chapter 12
lesson 6
Objective
you will be able to;
· describe induction qualitatively
· state Lenz's Law and apply it.
We have seen that:
· an electric current (moving charge) produces a
magnetic field.
Name the scientist.
·
· a magnetic field exerts a force on a moving charged
particle or an electric current along a wire.
Which LHR?
The next question is, “Can a magnetic field be
made to create a moving charge?”
An Englishman, Michael Faraday, and an
American, Joseph Henry, independently found
that it was possible to induce an electric
current with a magnetic field.
Michael Farady
22 September 1791 – 25 August 1867
Joseph Henry
17 December 1797 – 13 May 1878
Induction Coil
When the switch is closed (current), the needle on the galvanometer
goes to one side (very quickly) and then returns to zero.
When the switch is reopened (no current), the needle goes to the
other side briefly and then returns to zero.
When there is no current OR a steady current, the galvanometer
remains at zero.
Why?
A changing magnetic field induces a current.
As long as the field is changing a potential
difference will be created.
Potential Difference
The potential difference is created as a result of the
3rd LHR. The motion of the conductor is indicated by
the thumb, the direction of the fixed magnetic field by
the fingers and the potential difference is indicated
by the direction the force is acting on the electrons.
(the direction your palm will push.)
Example
A 50 cm length of conducting wire is moved at 30 m/s
through a magnetic field of 0.40 T, directed into the
page as shown. Calculate the direction of the
current flow
Lenz's Law
Simply stated: A changing (moving) magnetic
field will cause current to flow in a conductor in
a direction that creates an opposing magnetic
field. (The magnetic field in the coil will always
be set up so that work must be done. ie. The
magnet cannot be pulled into the coil it must be
pushed against a resisting force.)
Copper Tube Demo Explanation
Assignment
Read pages 615-619
Do p. 620 #1-7