Topic 12: Electromagnetic Induction

!!

12.1 Induced emf

Explore

1. A video documentary detailing the life and times of Michael Faraday, the father of electromagnetic induction. He rose up from poverty, without education, to become one of the most respected and talented scientists of his time.

Reflect upon Michael Faraday's achievements. Perform a search of the internet to find a list of them. 2. One such achievement was his contribution to the Royal Institution Christmas lectures. The society opened its doors once a year to the poor and the young. Faraday was a key figure in education and never forgot his roots and where he had come from. He gave back to society as much as he had gained.

Michael Faraday giving his Christmas lectures. You can see on the table many of the demonstrations and examples that he gave. In the audience, you can see the many young faces of children.

Challenge

"Devise and construct a series of demonstrations like Faraday's. They should

show the factors that affect the magnitude of the emf induced. Then give the presentation"

The lecture demonstration will be to a class of year 11s undertaking review upon section 6 of their IGCSE. This task will contribute 2 hours towards your PSOW. You should: • Ensure the demonstrations work properly. • Review the IGCSE syllabus to ensure that all aspects are covered. • Ensure that you are more knowledgable about the subject than they are! Things to consider: • Spend a good amount of time researching the topic. • Plan what you are going to build before you start it. • Divide the task amongst the group members. IGCSE Syllabus Section 6d Electromagnetic Induction

Flip

Readings:

IB Studyguide - page 1 (100) College Physics - Chapters 23.1 to 23.3

Apply

1. Complete the Topic 12.1 question packet. 2. Try the multiple choice quiz below only when the exercise above is complete. You will only get one chance.

End of Cycle

Your teacher will give you a written quiz. The results of the quiz will be recorded and will contribute towards your report's effort grade.!

1

Topic 12.2 Alternating Current Multiple Choice Quiz 1. When a coil is rotated in a uniform magnetic field at a certain frequency, the variation with time

t of the induced emf E is as shown below.

E

0 0 t

The frequency of rotation of the coil is reduced to one half of its initial value. Which one of the following graphs correctly shows the new variation with time t of the induced emf E?

E

E

E

E

0

0

0

0

0

0

0

0

t

t

t

t

A.

C.

B.

D.

(1)

2

2. The diagram below shows the variation with time t of the emf E generated in a coil rotating in a uniform magnetic field.

E

t00

e

杄

T2

T 32T

What is the root-mean-square value Erms of the emf and also the frequency f of rotation of the coil?

Erms f

A. e T2

B. e T1

C. 2

e T2

D. 2

e T1

(1)

3. A resistor is connected in series with an alternating current supply of negligible internal resistance. The peak value of the supply voltage is Vo and the peak value of the current in the resistor is I0. The average power dissipation in the resistor is

A. 2

00 IV

B. 2

00 IV

C. 00IV .

D. 2 00IV . (1)

3

4. An AC generator produces a voltage of peak value V. The frequency of rotation of the coil of the generator is doubled. The rms value of the voltage produced is

A. .22

V

B. .2V

C. .2V

D. .22V (1)

5. The graph below shows the variation with time t of the current I in a resistor.

00 t

I

–I

+I

0

0

Which of the following is the root-mean-square value of the current I?

A. 02I

B. I0

C. 0I

D. 20I

(1)

������ ��

Topic 12.2 Alternating Current End of Cycle Quiz 1. A bar magnet is suspended above a coil of wire by means of a spring, as shown below.

Spring

Magnet

Coil

The ends of the coil are connected to a sensitive high resistance voltmeter. The bar magnet is pulled down so that its north pole is level with the top of the coil. The magnet is released and the variation with time t of the velocity v of the magnet is shown below.

v

t0 0

(a) On the diagram above,

(i) mark with the letter M, one point in the motion where the reading of the voltmeter is a maximum;

(ii) mark with the letter Z, one point where the reading on the voltmeter is zero. (2)

������ ��

(b) Explain, in terms of changes in flux linkage, why the reading on the voltmeter is alternating.

.....................................................................................................................................

.....................................................................................................................................

.....................................................................................................................................

..................................................................................................................................... (2)

(Total 4 marks)

2. This question is about alternating current.

(a) The graph shows the variation with time t of the output voltage V of an ac generator of negligible internal resistance.

A resistor of resistance 25 � is connected across the output of the generator.

Calculate

(i) the rms value of the current in the resistor.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

������ ��

(2)

(ii) the average power dissipated in the resistor.

...........................................................................................................................

........................................................................................................................... (1)

(iii) the power dissipated in the resistor at 0.40 ms.

...........................................................................................................................

...........................................................................................................................

...........................................................................................................................

........................................................................................................................... (2)

(b) The frequency of rotation of the generator coil is now doubled. Sketch, using the axes in (a), the variation with t of the new output voltage V.

(2) (Total 7 marks)

������ ��

1. (a) (i) M shown at peak or trough; 1

(ii) Z shown on t-axis; 1

(b) by Lenz’s law, emf (or current) must change direction as flux cutting changes direction; as magnet oscillates, flux is cut in opposite directions; 2

[4]

2. (a) (i) I0 = 25

100 = 4.0(A);

Imax = 2.8 A; 2

or

Vmax = 2

100 = 70.7 V;

Imax = 25

7.70rms R

V= 2.8A;

(ii) 200 W; 1

(iii) V = 60(±2.0)V;

P = »¼

º«¬

ª »

¼

º«¬

ª25

6022

RV = 140(±10)W; 2

(b)

peak voltage of 200 V; (allow 180 to 200 V) period = 0.50 ms; 2

[7]

12.2 Alternating Current

Explore Use a combination of the two simulations linked below to explore the following variables upon the induced emf. You should try to explain the phenomena using the ideas of magnetic field, electrons and magnetic flux. Also consider the rate of change of emf. 1. Effect of speed of rotation. 2. Effect of strength of magnet. 3. Effect of area of loop. 4. Effect of number of loops.

s

Flip

Readings:

IB Studyguide - page 2 (101)

College Physics - chapter 23.5

Watch the VoiceThread video. Describe the construction and basic operation of the ac generator shown. All contributions will be watched in class. You should mention some of the factors affecting the induced emf that were explored earlier. Upon completion of the exercise, you should take the embed code and place the VoiceThread onto your own blog.

Studywiz)wouldn’t)allow)VoiceThread)to)work)properly)at)the)time)of)printing)this.)

Apply 1. Complete the Topic 12.2 question packet. 2. Try the multiple choice quiz below only when the exercise above is complete. You will only get one chance.

End of Cycle

Your teacher will give you a written quiz. The results of the quiz will be recorded and will contribute towards your report's effort grade.)

12.3 Transmission of electricity

Explore Use the equipment provided by the teacher to experimentally reproduce the set-up shown below. This website might be useful. Obviously you can't have 11,000V in the classroom, but the ratio of voltage change can be achieved using the transformers provided and the appropriate number of turns.

The set up you have reproduced effectively models and demonstrates the usage of transformers in the transmission of electricity and its usage in the National Grid.

Flip

Readings: IB Studyguide Topic 12 - pages 2 & 3 College Physics - chapter 23.7

Apply 1. Compete the Topic 12.3 Question Packet. 2. Try the multiple choice quiz below only when the activity above is complete. You will only get one chance.

End of Topic Your teacher will give you a written quiz. The results of the quiz will be recorded and will contribute towards your report's effort grade.!