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QCP 521: Teaching of Physics II

Lesson Plan on Electromagnetic Induction

Lin Yucheng EugeneTG02 / LG 02

Sub-group 2

Micro-teaching time slot: 14 Oct 2005, 8.30amMicro-teaching portion: Slides 8-10 with in-class worksheet

Table of Contents

Introduction.................................................................................1Development of Lesson Plan.......................................................3References...................................................................................8

AnnexesAnnex A - Powerpoint SlidesAnnex B - Screen Capture of Solenoid Video DemoAnnex C - Screen Capture of Iron Ring AppletAnnex D - Screen Capture of Solenoid AppletAnnex E - Screen Capture of A.C. Generator AppletAnnex F - In-class worksheetAnnex 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 ammeterInduced 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


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:

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. Zoom-ins 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

http://home.a-city.de/walter.fendt/phe/generator_e.htm

http://micro.magnet.fsu.edu/electromag/java/faraday2/

http://micro.magnet.fsu.edu/electromag/java/faraday/


Development of Lesson Plan

Segment Details/Description of Lesson Resources Duration(a) Recap of last

lesson's 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.

Slide 2 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.

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.

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.

4. State what we would be learning in today’s lesson.

Slide 3

Slides 4 - 5

Slide 6

Slide 7

5 min

(c) Lesson proper covering SIO (a)

5. Introduce Faraday as a British scientist who conducted two important experiments in 1831.

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.

Slides 8 – 9Java applet on Faraday’s iron ring experiment

5 min

3


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.

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.

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

Slide 10Java applet on Faraday’s solenoid experiment

Demo with solenoid and magnets.

Students to fill in worksheet part 1. (Annex F)

Worksheet part 2 (Annex F)

10 min – 15 min

10 min

4


Segment Details/Description of Lesson Resources Durationinfluences 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.

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.

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

(d) The a.c. generator - covering SIO (c)

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.

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

Slide 13

Slide 14Applet on a.c.

10 min

10 min

5


Segment Details/Description of Lesson Resources Durationthat the pair of opposite pole magnets 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.

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)

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.

generator

(d) Closure Summarise what was taught for this lesson: 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.

Slide 15 5 - 10 min

6


Segment Details/Description of Lesson Resources Duration

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.

Homework Assignment(Annex G)

7


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

http://www.tuaspower.com.sg/

http://www.senokopower.com.sg/




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


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 in-class 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


Annex C – Screen Capture of Iron Ring Applet

Java applet showing Faraday’s iron ring experiment.


C-1



Annex D – Screen Capture of Iron Ring Applet

Java applet showing Faraday’s solenoid experiment.


D-1



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

http://home.a-city.de/walter.fendt/phe/generator_e.htm

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