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Physics Lesson Plan
Teacher
Howard
Unit Title
Length
Goal(s)/PLO(s):
Course
Grade Level
Block/Period
Phys 12
12
L1 analyse electromagnetism, with reference to
magnetic fields and their effects on moving
charges
 state the rules explaining how magnetic
poles interact with each other
 describe and illustrate the direction of the
magnetic field lines for a permanent magnet
 use the right-hand rule to determine the
magnetic field direction for a current-carrying
wire or a solenoid
Date
Class Size
Lesson #, of
20-01
 determine the direction of the force exerted
on a current-carrying conductor or a moving
charge that is within a magnetic field
 solve problems that deal with a currentcarrying conductor placed in a magnetic field
and that involve
– magnetic force
– current
– length of conductor in the field
– magnetic field
Materials:
Magnets, compases
Timeline
Class Activities
Introduction
Body
Notes 20-01 to 20-3
Closure
Questions1-7, Problems 1-7 odd
Chapter 20 Magnetism
The first magnetic material were first discovered in Magnesia
thousands of years ago. 200 years ago it was discovered that
magnetism is related to electricity
• Their discovery led to devices like compasses, motors,
speakers, computer memory and electric generators.
20-1 Magnets and magnetic fields
All magnets have two poles
• where the magnetic effect is strongest
• originally names north and south because they pointed
towards the north and south poles respectively
• magnet-and-compass_en.jar
• They misnamed it at first (again)
o the North Pole is really a magnetic south pole
o The magnetic poles don’t line up (900km away)
perfectly with the axis of rotation (true geographic
poles) so you have to make different adjustments,
depending on location, to find true north.
• Opposites attract, like poles repel
o similar to, but not identical to electric charges
 monopoles have never been isolated
• if you cut a magnet in half you created new
N and S poles
Only a few materials are strongly magnetic (ferromagnetic
materials)
• iron, cobalt, nickel, gadolinium
• Others have very weak magnetic effects
The concept of fields can be applied to
magnetism
• magnetic field lines point in the
direction the north pole of a
compass needle would point
o tangent to curved field lines
• The number of lines in an area is
proportional to the strength
The magnetic field lines continue inside a
magnet.
Approximately uniform magnetic fields can
be made between two close, wide poles
20-02 Electric Currents Produce Magnetic Fields
1n 1820, Hans Oersted noticed that when current passed through a
wire his compass needle moved
• An electric current produces a magnetic field
The Right Hand Rule
When the thumb of your right hand points in the direction of the
conventional (+ to -) current, your fingers curl in the direction of
the magnetic field.
20-03 Force on Electric Current in a Magnetic Field
If an electric current can exert a force on a compass needle then, by
Newton’s 3nd Law, a magnet should exert a force on a current
carrying wire.
2nd Right Hand Rule
The direction of the force on a current carrying wire (thumb) in a
magnetic field is perpendicular to the direction of the current
(pointer) and perpendicular to the direction of the magnetic field
(middle).
The magnitude of the force is proportional to the current I and the
length of the wire l exposed to the uniform magnetic field. The
force also depends on the angle θ between the current direction and
the magnetic field.
If I and B are perpendicular then sin θ =1 and
The SI unit for magnetic field B is the tesla (T), but the gauss is
sometimes used.
The earth’s magnetic field is ½ G or 0.5 E-4 T. Good
electromagnets produce around 2T and the best around 10T.
Example 20-1
We need to work in 3 dimensions but the page only has 2 so we
use the analogy of arrows to show movement in and out of the
page.
represents the tip of an arrow coming out of the page
represents the tail of an arrow going into the page
Example 20-2
Questions 1-7, Problems 1-7odd