Theoretical material for the lesson,
definitions for concepts
The subjects of magnetism and electricity
developed almost independently of each other until 1820, when a Danish
physicist named Hans Christian Oersted discovered in a classroom demonstration
that an electric current affects a magnetic compass. He saw that magnetism was
related to electricity. We will begin by looking at permanent magnets and then
look at Oersted’s experiment.
Magnets have a north and a south pole.
Like magnetic poles repel each other and unlike poles attract each other. The
names of the poles come from the fact that the earth has a magnetic field. The
part of the magnet that will align toward the north pole of earth is called the
north pole of the magnet.
Some atoms, depending on their electronic
structure, act like magnets and have a north and south pole. In most matter,
there is no alignment of the poles of the atoms. In a bar magnet, the atoms
will line up. Sometimes this alignment can be achieved by simply banging on a
piece of iron. This can cause enough of the atoms to line up with the earth’s
field for the magnetic field of the iron to be measured.
The iron atoms in an unmagnetized
iron bar are randomly oriented, whereas in a magnetized bar they are aligned
with their north poles pointing in the same direction. The ability of iron
atoms to remain aligned in this way is responsible for the magnetic properties
Oersted discovered that a compass needle
below a wire (A) pointed north when there was not a current, (B) moved at right
angles when a current flowed one way, and (C) moved at right angles in the
opposite direction when the current was reversed.
The Right Hand Rule:
What we can determine from this is that an
electrical current produces a magnetic field . A magnetic field
surrounds the wire as shown below
A magnetic compass shows the presence
and direction of the magnetic field around a straight length of
This effect can be summarized by the right
hand rule. This rule states that if you put the thumb of your right hand in
the direction of the current, the magnetic field will wrap around the wire the
same way your fingers will.
Use (A) a right-hand rule of thumb to determine the
direction of a magnetic field around a conventional current. Remember that most
people write current going from positive to negative. If your stubbornness
requires you to thing about electron flow, you will have to reverse everything
and use the left-hand rule of thumb.
Forming a wire into a loop causes the magnetic field to
pass through the loop in the same direction. Notice that all sides of the
loop, by using the right hand rule, push the magnetic field the same
direction. This gives one side of the loop a north pole and the other side a
south pole. The magnetic field of the loop is the same of that as a bar
When a current is run through a cylindrical coil of wire, a
solenoid, it produces a magnetic field like the magnetic field of a bar magnet.
Magnetic force and current.
Because a wire carrying a current away from you,
represented by the black dot, has a magnetic field it will be affected by the
magnetic field of a magnet. The yellow and red boxes represent the ends of the
magnet. The field of the magnet is in green. The circular magnetic field of
the wire is shown. Notice how at the top the fields are lined up and repelling
and at the bottom the fields are opposite and attracting. The wire, if it can
move, feels a force down called the Lorentz force. This force is perpendicular
to both the magnetic field of the magnet and the current of the wire.
An electric motor, is a machine which converts
electrical energy into mechanical (rotational or kinetic) energy. A current
causes the coil to rotate mechanically. For this to occur
In the motor a current is passed through a
loop, which is immersed in a magnetic field. A force exists on the top leg of
the loop, which pushes the loop left, while a force on the bottom leg of the
loop pushes the loop right. The net effect of these forces is to rotate the
loop in the direction indicated. At some point, to keep the loop rotating it
is necessary to switch the direction of the current. This is done on this
applet when the loop is horizontal.
refers to the production of a current in a wire when there is relative motion
between the wire and a magnetic field. This connection was discovered by
Faraday, who found that changing magnetic fields though loops of wire will
cause currents to be induced.
In the above picture, a current is induced in a coil of
wire moved through a magnetic field. The direction of the current depends on
the direction of motion. These induced currents only exist as long as the
magnet is moving, and will die off when the magnet becomes stationary.
It is interesting to note that the current flows so as to
create a magnetic field to oppose the change created by moving the bar magnet.
This feature that the magnetic effects of the induced current are such as to
oppose the external change is known as Lenz's law. The induction of
currents from changing magnetic fields has a number of important applications,
including, odiously, the electrical generator.
(A) Schematic of a simple alternator (ac generator)
with one output loop. (B) Output of the single loop turning in a constant
magnetic field, which alternates the induced current each half cycle.
A transformers useful for changing the voltage of an
alternating current circuit. In a transformer an alternating current in
one coil of wire creates a changing magnetic field. This changing magnetic
field induces an alternating current in another nearby coil. Depending on the
ratio of turns of the coils, the induced current can have a voltage that is
larger, smaller, or the same as that of the primary current.
(A) This step-down transformer has 10 turns on the
primary for each turn on the secondary and reduces the voltage from 120 V to 12
V. (B) This step-up transformer increases the voltage from 120 V to 1,200 V,
since there are 10 turns on the secondary to each turn on the primary.
Additional guidelines for organizing a
Students can deduce topic of the lessen
and objectives, for clarification you can show topic and the learning objectives on the presentation.
vocabulary & terminology will be presented to the students and their
activities during the research work will be explained.
Then teacher will give
the worksheet on the concepts studied previously. Students attempt the
questions in groups as they engage in discussion. The teacher helps the
learners with difficulties in answering the questions.
Reinforce the LO’s: answer any questions
students may have/clarify understanding. Students reflect
on their learning.
At the end of the lesson teacher will give homework.
Additional multilevel (on
Each chapter has extra tasks which you
would use for high level students.
Recommendations for formative assessment
1)Use the answers provided to assess students’
understanding and the manner of application of the all terms concept knowledge
2)Provide a general feedback for every given point
(pay attention to give a fully explained feedback to the points that were not
3)You can change the numbers in calculations
according to the student’s ability
Answers, criteria for
assignments, additional materials for the lesson
experienced by PQ = force experienced by RS (but in opposite
No force experienced by QR and PS (since current is parallel to
the field). 
torque = one of the forces × perpendicular distance between forces = (BIL)x 
torque = BI(Lx),Lx = area of loop = A 
torque = BIAµ A 
The torque is directly proportional to the area of the loop.
3 a F=mg= (103.14 – 102.00) ´ 10–3´ 9.81soF= 1.12 ´ 10–2 N 1.1 ´ 10–2 N 
b B=  B=  B= 2.73 ´ 10-2 T(27 mT) 
4 F=BQv 
0.18 ´ 1.6 ´ 10–19´ 4.0 ´ 106 
1.15 ´ 10–13 N 1.2 ´ 10-13 N 
5a In order for the positively charged
ions to emerge from the slit,
the net force perpendicular to the velocity must be zero. 
force on ion = magnetic force on ion 
charge Q cancels.
electric field strength is E=.
Therefore, the magnetic flux density is:
B= 3.47 ´ 10–2 T or 35 mT 
b v= so r=  Δr= 
6a distance = speed ´
time = 2.0 ´ 1.0 = 2.0 m 
b Area swept = length ´
distance travelled = 0.10 ´ 2.0 = 0.20 m2 
c Change in magnetic flux = area swept ´ magnetic flux density 
change in magnetic flux = 0.20 ´ 0.050 = 1.0 ´ 10-2 Wb 
d Magnitude of e.m.f. = rate of change of magnetic flux linkage  E= (N= 1) E== 1.0 ´ 10-2 V (1 Wb s-1= 1 V)