magnetic effects of current

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ELECTROMAGNETISM

YEAR 11

[Pick the date]

PREETI MANOJ

THE OXFORD SCHOOL - DUBAI

PREPARED BY PREETI MANOJ

Electromagnetism Unit Plan

. UNIT OVERVIEW

A. Unit Plan Summary

This unit plan for Electromagnetism is designed for a high school course in General Physics. A conceptual, as

opposed to historical or thematic, teaching approach has been chosen for the instructional material and activities

of the unit, although some historical anecdotes, as well as themes such as motors and electric power, will be

included. The unit is targeted toward year 11 physics students with two years of algebra, but no calculus

preparation.. The textbook, which will be used primarily as a reference source rather than a curriculum guide, is

IGCSE PHYSICS by Stephen pople.

B. Goals

The goals for the unit may be logically grouped into three main categories: content knowledge, process skills,

and scientific dispositions.

Rationale

1) Needs of the Student

The content knowledge, process skills, and scientific dispositions learned in this unit are of vital interest to the

student. Students will experience the pleasure of knowing the how and the why behind many important aspects

of modern civilization, including the essential concept of energy conservation. Other widely-applicable topics

which underlie today's technology that will be addressed are motors, generators, and electrical power

generation.

Students also will benefit from acquiring the process skills we will cultivate in this unit. With these skills,

students will gain confidence in their ability to act, to put thought into practice. The possession of real-life,

practical skills will prove to be useful when solving problems and searching out answers to problems far beyond

the classroom. Such skills also allow students to be in a position to help others if and when the need arises.

Students can carry the scientific dispositions stressed in this unit into many other areas of their lives. Critical

thinking and objectivity are essential in weighing the claims of all sides of any issue, scientific or otherwise.

They also allow a student to thoughtfully examine his/her own views and the views of others, to search out and

analyze the points of disagreement, and to implement any changes needed for the student to construct a

consistent, rational outlook on life - a process that eludes subjective thinkers. Finally, those who can work well

with others make effective workers as well as managers, and are in high demand in the workplace.

2) Needs of the Society

The process skills developed in this unit will benefit society as well as the individual student. If problems in our

society are to be addressed, people who can think and act are required. This becomes clear when we

acknowledge the fact that thinkers, by themselves, accomplish nothing if people remain passive. The process

skills encouraged during this unit will help alleviate passivity by giving students the confidence to act as well as

think.



3) Needs of the Subject Area

Electricity and magnetism are essential not only to physics, but to all scientific disciplines. Much of the high-

technology laboratory equipment of any area of science is largely based on the concepts of this unit. Knowledge

of the ideas here will aid the scientist in fully understanding his/her equipment, and will help insure that the

resulting data will be interpreted correctly and properly analyzed.

Process skills, too, carry over into any scientific field. Understanding the theory behind one's equipment is of

little use if one fails to know how to use the apparatus for investigating research questions.

The dispositions taught in this unit will hopefully serve to continue the tradition previously established by

science. Most scientists of the past have endeavored to search for the answers to Nature's mysteries in an "as-

objective-as-humanly-possible" fashion. Although science would not be the same discipline without a healthy

dose of competition, science has also benefited, and will continue to benefit, from healthy doses of cooperation.

We hope that the dispositions acquired by the students during this unit will serve to reinforce these traits of the

scientific community

IV. MAJOR OBJECTIVES

By the end of this instructional unit, the student will be able to demonstrate the following objectives in writing,

and under test conditions, unless otherwise specified.

Content Knowledge Objectives

Given the direction of the current and the shape of a current-carrying conductor such as a straight wire or a

solenoid, sketch the configuration and direction of the induced magnetic field around the conductor.

Given the direction of the current in a conductor and the location and direction of the magnetic field, explain the

induced magnetic force in terms of the direction of the force and what materials are affected by the force.

List two factors that affect the magnitude of a current induced by moving a conductor through a magnetic field.

Explain how a galvanometer works using terms such as permanent magnet, pointer, pivot, coil, control spring,

induced magnetic field, and magnitude of allowable current.

Explain Lenz's Law in terms of the types of circuits to which it applies, the direction of the induced current and

the resulting force from that current, and how the Law is related to the idea of conservation of energy.

Describe an electric generator using terms such as mechanical energy, electrical energy, armature, slip ring, and

field magnet.

Describe an electric motor using terms such as mechanical energy, electrical energy, armature, slip ring, and

field magnet.

Explain how a transformer conforms to the idea of the conservation of energy.

List three fuel sources commonly used to produce electric power today.



Explain why the long-distance transmission of electric power is done using very high voltages by using the

terms transformer, current, heat loss, and efficiency.

Process Skill Objectives

Demonstrate electrical safety in the laboratory by performing the following behaviors during a laboratory test:

check for damp hands or a wet floor, turning off and unplugging electrical/magnetic equipment when adjusting

apparatus, and keeping one hand behind back at all times.

Given an input a-c current or voltage, sufficient wire, and a magnetic iron core, produce a transformer that will

theoretically provide a given output current or voltage.

Initiate and carry out one experiment using the scientific method by identifying a problem, determining an

approach and appropriate apparatus, proposing an hypothesis, setting up the apparatus, measuring and recording

the observed data, and drawing a logical conclusion from the gathered data.

Disposition Objectives

Given a complete description of an occurrence, analyze the situation, distinguishing clearly between

observation and inference, and write an hypothesis as a possible explanation for the occurrence.

Under anonymous conditions, write a one-page essay on what you liked/disliked in this instructional unit, what

changes could be incorporated that would better serve your needs, and how the studies in this unit changed or

did not change your appreciation and knowledge of science and E/M technology.

PROJECT OF THE MONTH

types of power plants - find advantages and disadvantages

Task: The tasks involved in this project are as follows:

Identify the pros and cons of various types of power plants, choose one type of plant for the project, and justify

your choice in a 3-page paper

Explain, in a 3-page paper (not including diagrams) how a large-scale electric generator works

Explain, in a 2-page paper, how electromagnetism is involved in the transmission of electric power from the

power plant to the consumer

Purpose: The purpose of this cooperative project is to relate the concepts we have learned in physics to

practical, real-world applications. We will also gain a basic understanding of how the various educational

disciplines come into play when we address a true-to-life situation

PROJECTS (The students can select)

1. You can make a simple electromagnet, make an electric catapult, take pictures of a magnetic field

or make any other device that uses an electromagnet.

Your display can include a drawing of your experiment and a working model that works and

everyone can test. Materials needed for this project can be found at home or purchased locally.



2. Making an electric motor is easy, fun and an exciting experiment. There are varieties of

technologies used in manufacturing of electric motors. You will identify and report those as your

project 3. Efficiency of a motor 4. What happens to the efficiency of a motor as you change the mass it lifts.



LEARNING OBJECTIVES:

Describe the pattern of the magnetic field due to currents in straight wires and in solenoids.

Describe applications of the magnetic effect of current, including the action of a relay.

State the qualitative variation of the strength of the magnetic field over salient parts of the pattern.

Describe the effect on the magnetic field of changing the magnitude and direction of the current.

1. The diagram below is a current carrying wire coming out of the page. Draw the magnetic field lines that will

be generated by this wire. Be sure to indicate the direction of the field lines.

2. The diagram below is a loop of current-carrying wire. Arrows indicate the direction of the current. For

each location, A through E, indicate in the spaces below whether the magnetic field generated by the loop

of wire is directed into the page, out of the page, upward, downward, to the right, or to the left.



3. The diagram shows a cell connected to a copper wire which passes vertically through a horizontal card.

When the current is turned on, magnetic field lines are produced around the wire.

(a) (i) Add an arrow to the wire AB to show the direction of the conventional current. (1)

(ii) Add an arrow to one of the magnetic field lines to show the direction of the magnetic field. (1)

(b) (i) What is shown by the direction of a magnetic field line?

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

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

(ii) How can the shape and direction of one of the field lines on the horizontal card be demonstrated?

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

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

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

.................................................................................................. (4)

4. The diagram shows an insulated copper coil wound on a plastic core and connected to a cell and a

switch.



(a) (i) Add an arrow to the wire AB to show the direction of the current when the switch is closed. (1)

(ii) In the dotted box, add two lines to represent the shape and direction of the magnetic field when the current

passes through the coil. (2)

(b) List three ways in which the strength of the magnetic field produced could be increased.

1 ....................................................................................................................................

2 ....................................................................................................................................

3 .................................................................................................................................... (3)

5. Fig. 5.1 shows a wire passing through a hole in a horizontal, plastic board.

Fig.5.1

The wire carries a current vertically upwards. A student moves a small compass around the board and plots the magnetic field lines due to the current. (a) (i) Draw a diagram of the board as seen from above and mark on it the magnetic field lines due to the current. [3] (ii) The current is increased. Describe how the magnetic field changes. [1] CHECKLIST

LESSON

OUTCOME

CHECKLIST

COMMENTS

Describe the pattern of the magnetic field due to currents in straight wires and in solenoids. Describe applications of the magnetic effect of current, including the action of a relay. State the qualitative variation ofthestrength of the magnetic field over salient parts of the pattern. Describe the effect on the magnetic field of



changing the magnitudeand direction of the current.



DAILY LESSON PLAN

SUBJECT: PHYSICS UNIT: electricity and

magnetism DATE:

TOPIC: Magnetic effects of current YEAR: GRADE 11

LESSON # ........ OF.......


Students should be able to:



State the qualitative variation of the strength of the magnetic field over salient parts of the pattern.

Describe the effect on the magnetic field

of changing the magnitude and direction

of the current

OUTCOME/S:

Students should be able to



State the qualitative variation ofthestrength of the magnetic field over salient parts of the pattern.

Describe the effect on the magnetic field of changing the magnitudeand direction of the current.

LESSON OUTLINE:

Structure Activities/Strategies

Starter

Begin by introducing new unit, Electricity and Magnetism. Ask students what kind of

experiences they have had with electricity. Ask for examples. Ask students what kind of

experiences they have had with magnetism. Ask for examples. Continue questioning. Do

the overhead electrical wires ever stick to, say, the garbage truck? Have you ever

received an electric shock from a refrigerator magnet? Have you personally witnessed

any demonstrable relationship between E and M? So why are electricity and magnetism

lumped together in this unit? Are they both equally unimportant and so we lump them

together to finish faster and get on to more important topics in physics? Suggest that



Main activity

Plenary

Extended

there may be no relationship between E and M.

Once the unit is introduced explain the magnetic fields produced around a wire and

around a coil.Show a PPT to reinforce the concepts learnt.

Students write the concepts in their notebook

VOCABULARY

Magnetic field

RESOURCES:

http://www.phy.ilstu.edu/pte/311unitplans/bergmann.html, PPT

EVALUATION/ HOMEWORK

Questions from the textbook

-

http://www.phy.ilstu.edu/pte/311unitplans/bergmann.html



LEARNING OBJECTIVE

Describe an experiment that shows that a changing magnetic field can induce an e.m.f. in a circuit.

State the factors affecting the magnitude of an induced e.m.f.

Show understanding that the direction of an induced e.m.f. opposes the change causing it.

1. (a) The diagram shows a coil of wire connected to a sensitive ammeter. A bar magnet is moved towards the coil.

What is observed on the ammeter?

......................................................................................................................................................................... [1]

(b) What is observed if:

(i) the magnet is removed from the coil?

......................................................................................................................................................................... [1]

(ii) the magnet and coil move in the same direction at the same speed?

......................................................................................................................................................................... [1]

(c) (i) What name is given to the phenomenon referred to in (b)?

......................................................................................................................................................................... [1]

(ii) State three factors which determine the size of the current produced.

1. ..................................................................................................................................................................... [1]

2. ..................................................................................................................................................................... [1]

3. ..................................................................................................................................................................... [1]

2. (a) To avoid cutting through cables, a gas company uses a device to detect their position before digging holes.

The magnetic field produced by the cable induces a voltage across the coil. This is registered on a meter

attached to the device.

The device cannot detect cables that carry a steady direct current. Explain the reason for this.

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

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

......................................................................................................................................................................... [2]

(b)Why is it better to use the coil vertically than horizontally?

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

......................................................................................................................................................................... [2]

(c)State two ways in which you could get a larger reading on the meter.

1. ..................................................................................................................................................................... [1]

2. ..................................................................................................................................................................... [1]

3. When a permanent bar magnet is moved into a solenoid as shown, a small deflection is recorded on the

sensitive galvanometer. Which change would increase the size of the reading?



a. Using the south pole instead of the north pole

b. Use less turns of wire

c. Pulling the magnet at the same speed at which it was inserted

d. Inserting a resistor in series with the galvanometer

e. Pushing the magnet in faster

Please justify your answer.

_______________________________________________________________________________________

_______________________________________________________________________________________

4. Which diagram correctly gives the direction of the induced current when the magnet is moved as shown?

(a) (b) (c) (d)

CHECKLIST

TOPIC

CHECKLIST

COMMENTS

Describe an experiment which

shows that a changing magnetic field can induce an e.m.f. in a circuit.





DAILY LESSON PLAN


magnetism DATE:

TOPIC: Magnetic effects of current YEAR: GRADE 11

LESSON # ........ OF.......



Describe an experiment that shows that a changing magnetic field can induce an e.m.f. in a circuit.



OUTCOME/S:


Describe an experiment which shows that a changing magnetic field can induce an e.m.f. in a circuit.


Show understand that the direction of an induced e.m.f. opposes the change causing it.

LESSON OUTLINE:


Starter

Main activity

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. Introduce Faraday as a British scientist who conducted two important experiments in 1831. 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. Introduce the notion of a changing magnetic field and the notion of electromagnetic induction.

4. Get students to deduce the various factors affecting the size of the induced



Plenary

Extended

current.

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

VOCABULARY

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.

RESOURCES:

www.teachersstupidchicken.com


Questions from textbook

-



LEARNING OBJECTIVE:

Describe a rotating-coil generator and the use of slip rings.

Sketch a graph of voltage output against time for a simple a.c. generator.

1. Determine the polarity of induced voltage between the ends of this wire loop, as it is rotated between the two magnets:

2. In order to make the most practical AC generator (or alternator, as it is also known), which design makes more sense: a stationary permanent magnet with a rotating wire coil, or a rotating permanent magnet with a stationary wire coil? Explain your choice.



3. (a) What is meant by an alternating current ?

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

......................................................................................................................................................................... [2]

(b)Which of the following graphs show an alternating current ?

4. If this wire (between the magnet poles) is moved in an upward direction, what polarity of voltage will the meter indicate?



Describe the factors influencing the magnitude of the voltage induced by motion, and determine whether this is an example of an electric motor or an electric generator.

CHECKLIST

TOPIC

CHECKLIST

COMMENTS

Describe a rotatingcoil generator and the use of slip rings. • Sketch a graph of voltage output against time for a simple a.c.

generator



DAILY LESSON PLAN


magnetism DATE:

TOPIC:A.C.generator YEAR: GRADE 11

LESSON # ........ OF.......



Describe the principle of operation of a simple a.c. generator (rotating coil or rotating magnet) and the use of slip rings (where needed)

Sketch a graph of voltage output against time for a simple a.c. generator (to be covered in next lesson on electromagnetic induction)

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)

OUTCOME/S:


Describe a rotatingcoil generator and the use of slip rings.

Sketch a graph of voltage output against time for a simple a.c. generator

LESSON OUTLINE:


Starter

5. 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.

6. Recall that they have learnt about how a hydroelectric dam works. Introduce



Main activity

Plenary

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.

Next, give example of where a.c. generators

. 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.

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.

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). 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.

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. 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:

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



Extended

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

VOCABULARY

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.

RESOURCES:

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


QUESTIONS FROM TEXTBOOK

-

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

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

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

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



LEARNING OBJECTIVE:

Describe an experiment to show that a force acts on a current-carrying conductor in a magnetic field, including the effect of reversing: (i) the current (ii) the direction of the field

Describe an experiment to show the corresponding force on beams of charged particles. State and use the relative directions of force, field and current. State that a current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by increasing the number of turns on the coil. Relate this turning effect to the action of an electric motor. Describe the effect of increasing the current

1. (a) A wire is positioned between two magnets. The wire is connected to a battery.

Describe what happens.

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

......................................................................................................................................................................... [2]

(b) (i) The connections are reversed. Describe what happens now.

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

......................................................................................................................................................................... [2]

(ii) The battery is replaced by a power supply that gives an alternating current. What is observed ?

......................................................................................................................................................................... [1]



2. (a) An electric motor is connected to the external circuit via a split ring commutator.

Explain the purpose of this.

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

......................................................................................................................................................................... [3]

(b) (i) How could the motor be used as a generator ?

......................................................................................................................................................................... [1]

(ii) The current produced would be a varying direct current (dc).

What changes would be needed for the generator to produce an alternating current (ac) instead ?

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

......................................................................................................................................................................... [2]

3. (a) A simplified electric motor consists of a coil of wire connected to a battery and positioned between two

magnets (see diagram).



(i) Use Fleming’s left-hand rule to predict the direction of the force on each arm of the coil.

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

......................................................................................................................................................................... [2]

(ii) State the direction of motion of the coil.

......................................................................................................................................................................... [1]

(b) (i) After half a turn the coil will stop.What piece if equipment do you need to use to keep the coil moving ?

......................................................................................................................................................................... [1]

(ii) What does the piece of apparatus do ?

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

......................................................................................................................................................................... [2]

4. (a) Name three machines, which make use of motors.

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

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

......................................................................................................................................................................... [3]

(b) Electric motors make use of carbon brushes.What two properties of carbon make it a good material to use?

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

......................................................................................................................................................................... [2]

(c) State one way in which a motor can be made more powerful.

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

......................................................................................................................................................................... [2]

CHECKLIST

TOPIC CHECKLIST COMMENTS

Describe an experiment to show that a force acts on a current-carrying conductor in a magnetic field, including the effect of reversing (i) the current, (ii) the direction of the field.

Describe an experiment to show the corresponding force on beams of charged particles. • State and use the relative directions of force, field and

current

State that a current-carrying coil in a magnetic field experiences a turning effect and



that the effect is increased by increasing the number of turns on the coil. Relate this turning effect to the action of an electric motor. Describe the effect of increasing the current.



DAILY LESSON PLAN


magnetism DATE:

TOPIC: d.c. motor YEAR: GRADE 11

LESSON # ........ OF.......



Describe an experiment to show that a force acts on a current-carrying conductor in a magnetic field, including the effect of reversing:

(i) the current (ii) the direction of the field

Describe an experiment to show the corresponding force on beams of charged Particles

State and use the relative directions of force,field and current.

State that a current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by increasing the number of turns on the coil.

Relate this turning effect to the action of anelectric motor

Describe the effect of increasing the current

OUTCOME/S:


Describe an experiment to show that a force acts on a current-carrying

conductor in a magnetic field, including the effect of reversing (i) the current, (ii) the direction of the field.

Describe an experiment to show the corresponding force on beams of charged particles.

State and use the relative directions of force, field and current.

State that a current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by increasing the number of turns on the coil.

Relate this turning effect to the action of an electric motor

LESSON OUTLINE:


Starter

Main activity

Introduce a motor as a device that transforms electrical energy to mechanical

energy.

Introduce the various components (diagram in slide 12) of the simple d.c. motor:

the permanent magnets, the rotating coil, the axle of rotation, split rings and

carbon brushes. Ask students to list machines that use the spinning motion of motors to

do work. Have students identify the kind of mechanical work done by the spinning parts

of each of these machines. (A power lawnmower's spinning blades cut grass; a car's

spinning wheels move the car down the street; a tape player's spinning spool advances



Plenary

Extended

the audio or video tape)

Summarise what was taught for this lesson.

Ask students to discuss what life might have been like before electric motors came into

common use. What might your community have been like

VOCABULARY

d.c.motor, split rings

RESOURCES:

www.pbs.org , PPT slides



-

http://www.pbs.org/



LEARNING OBJECTIVE:

Describe the production and detection of cathode rays

Describe their deflection in electric fields

State that the particles emitted in thermionic emission are electrons

Describe (in outline) the basic structure and action of a cathode-ray oscilloscope (detailed circuits are not required)

Use and describe the use of a cathode-ray oscilloscope to display waveforms



CHECKLIST



Describe their deflection in electricfields.

State that the particles emitted in thermionic emission are electrons.

Describe in outline the basic structure, and action, of a cathode-ray oscilloscope (detailed circuits are not required)

Use and describe the use of a

cathode-ray oscilloscope to display

waveforms.



DAILY LESSON PLAN


magnetism DATE:

TOPIC: Cathode ray oscilloscope YEAR: GRADE 11

LESSON # ........ OF.......




Describe their deflection in electric fields

State that the particles emitted in thermionic emission are electrons

Describe (in outline) the basic structure and action of a cathode-ray oscilloscope (detailed circuits are not required)

Use and describe the use of a cathode-ray oscilloscope to display waveforms

OUTCOME/S:



Describe their deflection in electricfields.

State that the particles emitted in thermionic emission are electrons.

Describe in outline the basic structure, and action, of a cathode-ray

oscilloscope (detailed circuits are not required)

Use and describe the use of a cathode-ray oscilloscope to display waveforms.

LESSON OUTLINE:


Starter

Main activity

Plenary

Extended

Ask the students how the television works.

Discuss the main parts of the oscilloscope.Explain the working and use of

oscilloscope as a measuring instrument.

Students summarise the concepts learnt.



VOCABULARY

Cathode ray tube, thermionic diode

RESOURCES

www.tes.co.uk



-



LEARNING OBJECTIVE :

Describe the construction of a basic iron-cored transformer as used for voltage transformations.

Recall and use the equation (Vp /Vs) = (Np /Ns).

Describe the use of the transformer in highvoltage transmission of electricity.

Give the advantages of high-voltage transmission.

Describe the principle of operation of a transformer.

Recall and use the equation Vp Ip = Vs Is (for 100% efficiency).

Explain why energy losses in cables are lower when the voltage is high.

1. Look at the following transformer. The source of electricity is on the left. Therefore, the primary coil is on

the left, and the secondary is on the right.

Fill in the following chart for this transformer. Would this be a step-up or step-down (circle one)?

2. For the above transformer what is the output voltage if it is only 75% efficient?



3. A transformer has a primary coil with 200 turns, and a secondary coil with 2000 turns. The input voltage is 120

VAC, and runs at 1800 Watts. What is the output voltage?

2. A transformer cannot be used to run a 230 V, 100 W mains lamp directly from a 12 V car battery.

Which one of the following is the correct reason for this?

a) The internal resistance of the battery will not allow enough current in the primary coil.

b) Eddy currents in the iron core will heat up the iron core.

c) The current from the battery will produce a steady flux in the secondary coil.

3. An alternating supply delivers a current of 0.025 A at 12 V to the primary coil of a transformer. A 20 Ω

resistor is connected to the secondary coil.

a) The current in the secondary circuit is 0.110 A.

the power input

power input = .................. W

the power output

power output = ................ W



the efficiency

efficiency = .................... %

b) The frequency of the supply is increased. The power input is kept constant. The current in the secondary coil

falls to 0.105 A.

Calculate the new efficiency of the transformer.

4.



CHECKLIST


Describe the construction of a basic iron-cored transformer as used for voltage transformations. Recall and use the equation (Vp/Vs ) =(Np/Ns).

Describe the use of the transformerinhighvoltage transmission of electricity. Give the advantages of high voltage transmission. Describe the principle of operation of a Transformer. Recall and use the equation VpIp = VsIs (for 100% efficiency). Discuss the energy loss in cables.

magnetic effects of current

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