Download EM Induction Lesson Plan

QCP 521: Teaching of Physics II
Lesson Plan on
Electromagnetic Induction
Lin Yucheng Eugene
TG02 / LG 02
Sub-group 2
Micro-teaching time slot: 14 Oct 2005, 8.30am
Micro-teaching portion: Slides 8-10 with in-class worksheet
Table of Contents
Introduction .................................................................................. 1
Development of Lesson Plan ....................................................... 3
References .................................................................................... 8
Annexes
Annex A - Powerpoint Slides
Annex B - Screen Capture of Solenoid Video Demo
Annex C - Screen Capture of Iron Ring Applet
Annex D - Screen Capture of Solenoid Applet
Annex E - Screen Capture of A.C. Generator Applet
Annex F - In-class worksheet
Annex G - Homework Assignment
Lesson Plan – Electromagnetic Induction
Introduction
Subject: Pure Physics
Topic: Electromagnetic Induction I
Level: Secondary 4 Express
Students' Ability: Average
Lesson Duration: 2 periods (~70 minutes)
Pre-requisite Knowledge:
1. Students have learnt how to describe conventional current direction in a simple
circuit, including using dots and crosses in three-dimensional space.
2. Students have learnt the fundamental properties of magnetism (direction of
magnetic field in relation to North and South Pole).
3. Students have learnt how to describe the magnetic fields produced by a current
carrying wire (Right Hand Screw Rule).
4. Students have been introduced to forces on a current-carrying conductor in a
magnetic field. Students are able to apply Fleming’s left-hand rule.
5. Students can demonstrate how a d.c. motor works.
Specific Instructional Objectives:
By the end of the lesson, students should be able to:
a. Deduce from experiments showing electromagnetic induction, such as a magnet
entering a solenoid:
(i) that a changing magnetic field can induce an e.m.f. in a circuit
(ii) that the direction of the induced e.m.f. opposes the change producing it
(iii) the different factors affecting the magnitude of an induced e.m.f.
b. Describe the principle of operation of a simple a.c. generator (rotating coil or
rotating magnet) and the use of slip rings (where needed)
c. Sketch a graph of voltage output against time for a simple a.c. generator (to be
covered in next lesson on electromagnetic induction)
d. Show how the voltage output is influenced by the speed of rotation, number of
coils, strength of magnetic field. (to be covered in next lesson on electromagnetic
induction)
New Concepts and Terms:
Zero-point galvanometer – A variant of an ammeter
Induced current – Electrical current created in a closed circuit due to a changing
magnetic field cutting the circuit.
Induced e.m.f. – Electromotive force created in a circuit (closed or opened) due to a
changing magnetic field cutting the circuit.
1
Lesson Plan – Electromagnetic Induction
Common Misconceptions:
Generating electricity requires no work.
When generating electricity, only the magnet can move.
Voltage can only be induced in a closed circuit.
Magnetic flux, rather than change of magnetic flux, causes an induced e.m.f.
Water in dams causes electricity.
Learning Aids and Resources:
1. Self-prepared Powerpoint slides (Slides handouts in Annex A)
2. Faraday’s solenoid experiment video demo using a galvanometer, a solenoid and
some magnets. (Screen Capture in Annex B)
3. Java applet on Faraday’s iron ring experiment extracted from:
http://micro.magnet.fsu.edu/electromag/java/faraday/
(Screen capture in Annex C)
4. Java applet on inducing an e.m.f. with a magnet entering a solenoid extracted
from: http://micro.magnet.fsu.edu/electromag/java/faraday2/
(Screen capture in Annex D)
5. Java applet on a.c. generator extracted from:
http://home.a city.de/walter.fendt/phe/generator_e.htm
(Screen capture in Annex E)
Worksheets:
1. In-class worksheet on factors affecting magnitude of induced e.m.f. and direction
of induced current (Annex F)
2. Homework worksheet on electromagnetic induction and a.c. generator (Annex G)
Reflection:
After my micro-teaching in class, some modifications can be made to improve on the
lesson:
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


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While loading the quicktime video demos, error boxes kept appearing.
Although the videos managed to run, the error boxes disrupted the general
flow of the lesson. Such problems could have been corrected by trying them
out a day before on the computer that was to be used for the demo.
If time permits, a short slide on the British scientist Faraday could be included
to introduce students to his work.
While explaining that electromagnetic induction is proportional to the rate of
change of magnetic field cutting a coil of wire, a diagram or even an
animation could be shown to better illustrate what is meant by magnetic field
lines cutting the coil.
As the galvanometer readings cannot be clearly seen in the videos, students
filling up the in-class worksheet could only fill in qualitative readings. Zoomins on the galvanometer could have been shown in the videos to give a clearer
picture of the magnitude of the deflections.
When concluding on the factors affecting the magnitude of induced current,
the extraneous variable of number of coils per unit length should have been
mentioned instead of the absolute number of coils.
2
Lesson Plan – Electromagnetic Induction
Development of Lesson Plan
(a)
Segment
Recap of last
lesson's
Details/Description of Lesson
1. Recap concepts taught in last lesson of force
on a current carrying conductor in a magnetic
field - Fleming's Left Hand Rule.
2. Mention that this lesson would be the inverse,
obtaining electricity from motion.
Resources
Slide 2
Duration
5 min
(b)
Lesson intro
1. Before starting on the topic proper, ask the
students the following questions:
- How do we get electricity in our homes?
- Where does electricity come from?
- How do we “create” electricity?
Pause and let students think about these
questions before recalling what they learnt in
Sec 3 on the transformation of mechanical to
electrical energy.
Slide 3
5 min
2. Recall that they have learnt about how a
hydroelectric dam works. Introduce a
generator as a device that transforms
mechanical energy to electrical energy.
Mention that the generator produces
alternating current which is transported to our
homes. The generator is known as an a.c.
generator. Briefly describe that we would be
learning how this generator works.
Slides 4 - 5
3. Next, give example of where a.c. generators
are used and where they could be found in the
Singapore context. Supplement with a
photograph of Senoko power station.
Slide 6
4. State what we would be learning in today’s
lesson.
Slide 7
5. Introduce Faraday as a British scientist who
conducted two important experiments in
1831.
Slides 8 – 9
Java applet
on Faraday’s
iron ring
experiment
(c)
Lesson proper
covering SIO
(a)
6. Show java applet on the web demonstrating
Faraday’s iron ring experiment. After the
applet, ask students what they observe. Recall
what they have learnt about induced
magnetism. Mention that the magnetic field
from the right coil creates a current in the left
coil as can be seen from the moving compass.
Explain the notion of induced current.
3
5 min
Lesson Plan – Electromagnetic Induction
Segment
Details/Description of Lesson
Resources
Duration
7. Slide 9 is provided as a summary for
explanation given in class.
8. Show java applets on the web demonstrating
Faraday’s solenoid experiment. After the
applet, link their observations to the previous
applet. Introduce the notion of a changing
magnetic field and the notion of
electromagnetic induction.
Slide 10
Java applet
on Faraday’s
solenoid
experiment
9. Demonstrate using real solenoid,
galvanometer and magnets, Faraday’s
solenoid experiment and get students to
deduce the various factors affecting the size
of the induced current from their
observations:
i. Project video demos. Show actual
apparatus in class so that students would
have a better understanding. If visualiser
is present, show one demo live.
ii. Get students to note the deflection of the
galvanometer when the bar magnet
(made up of 16 button magnets) enters
the solenoid, exit the solenoid, and when
it is stationary.
iii. Change to weaker magnet by using less
button magnets and repeat step ii above.
iv. Repeat step ii but with a much slower
speed at which the magnet enters and
exit the solenoid.
v. Change the solenoid to a self-made coil
of wire (less coils than solenoid) and
repeat step ii above.
Demo with
solenoid and
magnets.
10 min –
15 min
Students to
fill in
worksheet
part 1.
(Annex F)
10. After students have completed part 1 of the
worksheet, get students to summarise to the
class the 3 main factors affecting the size of
the induced current. Conclude for students
that the size of the induced current is directly
proportional to the rate of change of magnetic
field lines cutting the coil. As an extension
question to brighter students, ask them what
could be a fourth factor that could be used to
increase the magnitude of the induced current.
11. Mention that we were interested in the size of
the induced current in the above demos, now
we are interested in finding out about what
4
Worksheet
part 2
(Annex F)
10 min
Lesson Plan – Electromagnetic Induction
Segment
Details/Description of Lesson
influences the direction of the deflection.
Using a compass, indicate the poles of the
magnet. Show 2 video demos: one with the
north pole going in and out of the home-made
coil, one with the south pole.
Resources
Duration
i. Students are to note how the coil is
connected to the digital ammeter.
ii. Get students to note the direction of the
current. Guide students by hinting what
it means by positive and negative
readings on the ammeter.
iii. Recalling the right-hand grip rule, get
students to deduce the “pole” of the
solenoid when the magnet entered and
exited.
(d)
The a.c.
generator covering SIO
(c)
12. From the observations seen of the above
demos, summarise and conclude the various
factors affecting the size and direction of the
induced current and hence the induced e.m.f.
Slides 11 12
5 min
13. Recall the introduction of today’s lesson
about the a.c. generator. State that an a.c.
generator is a device that uses the Principle of
Electromagnetic induction to transform
mechanical energy to electrical energy. Add
that work needs to be done on the generator to
produce electricity. Recall examples of other
sources of mechanical energy: wind, tides,
rising steam, etc.
Slide 13
10 min
Slide 14
Applet on
a.c.
10 min
14. Emphasise the point that a changing magnetic
field can be achieved either from a moving
magnet or a moving coil in a fixed magnetic
field.
15. Introduce the various components (diagram in
slide 12) of the simple a.c. generator: the
permanent magnets, the rotating coil, the axle
of rotation, slip rings and carbon brushes.
Stress that a real generator consists of many
turns of coil (and not just one turn of coil).
The applet has only one for simplicity.
16. Show applet on a.c. generator. Use the applet
to demonstrate how the coil (made of wires)
rotate between the magnetic field - Point out
5
Lesson Plan – Electromagnetic Induction
Segment
Details/Description of Lesson
Resources
that the pair of opposite pole magnets
generator
constitutes a strong magnetic field and the
coil is made to rotate between it due to the
kinetic energy of falling water, rising steam or
wind for example.
Duration
17. Link what they have learnt about
electromagnetic induction to how an a.c.
generator produces electricity. - as the coil
rotates, the magnetic field through the coil
changes and therefore by electromagnetic
induction, an e.m.f is induced between the
ends of the coil.
18. Explain the use of the slip rings - slip rings
allow for the transfer of the induced current in
the rotating coil to the external circuit. Point
out that each ring is connected to one end of
the coil and electrically connected by a
conducting carbon brush against which it slips
to the external circuit.
19. Mention that interested students can use
Fleming's Right-hand rule to find the
direction of the induced current at positions
when the plane of the coil is perpendicular to
the magnetic field. (This is not in syllabus)
(d)
Closure
20. Bring students' attention to the fluctuation of
voltmeter reading and the red trace on the
graph at various positions of the coil. Show
students that the induced e.m.f. is oscillating
between negative and positive. The induced
current is this known as an alternating current.
Summarise what was taught for this lesson:
Slide 15
 What is meant by electromagnetic
induction
 The factors affecting electromagnetic
induction (explain that the fourth factor
would be to include a soft iron core in the
solenoid)
 How a simple a.c. generator works
Mention that the next lesson would continue on
this topic to cover sketching voltage output of an
a.c. generator as well as how transformers work.
6
5 - 10 min
Lesson Plan – Electromagnetic Induction
Segment
Details/Description of Lesson
Resources
If there is time, get students to think about the
differences in the voltage that is obtained from
wall plugs in the house and the voltage that is
supplied by their handphone batteries. Ask them
how we can transform the voltage from the wall
plug into a voltage that can charge a handphone.
(e)
Assessment
Students are to do a worksheet for homework and
hand in at the next lesson.
7
Homework
Assignment
(Annex G)
Duration
Lesson Plan – Electromagnetic Induction
References
1. Chew, C., Leong, S. C. & Chow, S. F. (2000). Physics - A Course for 'O' Level
(2nd edition). Federal Publications. Singapore.
2. Chew, A. (2005). O-Level Classified Physics: Past Examination Questions.
Singapore Asian Publications. Singapore
3. http://www.walter-fendt.de/ph14e/generator_e.htm
4. http://micro.magnet.fsu.edu/electromag/java/faraday/
5. http://micro.magnet.fsu.edu/electromag/java/faraday2/
6. http://www.senokopower.com.sg
7. http://www.tuaspower.com.sg
8. Cliparts from http://www.clipart.com
8
Lesson Plan – Electromagnetic Induction
Annex B – Screen Capture of Video Demo
Part 1 – Getting students to deduce the factors affecting size of induced e.m.f.
4 video demos will be shown in class. Students are to fill in the in-class worksheet
provided in Annex F and deduce the factors affecting the size of the induced e.m.f.
The 4 demos are:
- Solenoid connected to galvanometer. 16 button magnets, linked together,
are inserted, left inside and removed at an average speed. (see capture
below)
- Solenoid connected to galvanometer. 6 button magnets, linked together, are
inserted, left inside and removed at an average speed.
- Solenoid connected to galvanometer. 16 button magnets, linked together,
are inserted, left inside and removed at a slow speed.
- Home-made coil with few turns of wire connected to galvanometer. 16
button magnets, linked together, are inserted, left inside and removed at an
average speed.
(The visualiser, if present, would be used to show the first demo to give students a
better idea of the circuit and apparatus.)
B-1
Lesson Plan – Electromagnetic Induction
Part 2 – Getting students to deduce the factors affecting the direction of induced
current
2 video demos will be shown in class. Students are to fill in the second part of the inclass worksheet provided in Annex F and deduce the factors affecting the direction of
the induced current.
Before starting this part of the demo, students will be shown with the aid of a compass
how to locate the north pole of the magnet.
The 2 demos shown are:
- Solenoid connected to digital ammeter. North pole of the magnet is
inserted, left inside and removed at an average speed. (see capture below)
- Solenoid connected to digital ammeter. South pole of the magnet is
inserted, left inside and removed at an average speed.
The start of the video shows clearly the direction in which the wire is coiled. Students
are then to note the sign of the current registered when the north/south pole enters and
exits the coil.
B-2
Lesson Plan – Electromagnetic Induction
Annex C – Screen Capture of Iron Ring Applet
Java applet showing Faraday’s iron ring experiment.
http://micro.magnet.fsu.edu/electromag/java/faraday/
C-1
Lesson Plan – Electromagnetic Induction
Annex D – Screen Capture of Iron Ring Applet
Java applet showing Faraday’s solenoid experiment.
http://micro.magnet.fsu.edu/electromag/java/faraday2/
D-1
Lesson Plan – Electromagnetic Induction
Annex E – Screen Capture of Simple A.C. Generator
Java applet showing a simple a.c. generator.
http://home.a city.de/walter.fendt/phe/generator_e.htm
E-1