15-Chapter 15 - Transformers

8/12/2019 15-Chapter 15 - Transformers

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Chapter 15

Magnetic Circuits

and Transformers


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Forces and Laws o f Physics

Lorentz Force The force on a moving charge in a magnetic field is proportionalto the charge, velocity, and magnetic field strength.

Faradays Law

Currents can be induced in wires by a changing magnetic fields.Lenzs Law

The induced currents in a conductor are in such a direction as to

oppose the change in magnetic field that produces them

Amperes Law The line integral of the magnetic field intensity around a closed

path is equal to the algebraic sum of the currents flowing

through the area enclosed by the path.


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Magnetic Compass

Desktop Demo

Try to balance a disk magnet on its side in your desk.

Try to suspend a magnet from a thread.


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1 Short Wire

1 D Cell Battery

1 Nail or Screw

1 Disk Magnet

Lorentz Force Motor

Construct the simple motor shown in the figure.

Put the magnet on the head of your nail.

Touch the sharp end of the nail to the negativeside of the battery.

Hold the wire to the positive side of the battery.

Lightly touch the wire to the edge of the magnet.

What are things that you can do to change thedirection of the motor?

How can you increase the speed of the motor?

Note: The magnets are about 50 cents each andare available at www.rare-earth-magnets.com
http://www.rare-earth-magnets.com/http://www.rare-earth-magnets.com/http://www.rare-earth-magnets.com/http://www.rare-earth-magnets.com/http://www.rare-earth-magnets.com/http://www.rare-earth-magnets.com/http://www.rare-earth-magnets.com/


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Chapter 15

Magnetic Circuits

and Transformers


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Lorentz Force

the force on a move charge in a magnetic field

right hand rule

force on electrons

force on current carrying wires Desktop Demo

What are two ways that you can change the direction of

the Lorentz force on a wire?

Buqf

sinquBf

Bif


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Lorentz Force Motor

Construct the motor below.


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How do you create a Magnetic Field?

Answer:

move electrical charges


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Draw the magnetic field lines for the

following:

A Current Carrying Wire

A Current Carrying Loop

An atom

A Permanent Magnet The Earth

A Coil of Wire

a.k.a. an Electromagnet, Solenoid, or Inductor


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Chapter 15

Magnetic Circuits

and Transformers


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Faradays Law Examples

Currents can be induced in wires by achanging magnetic fields.

Horseshoe magnet, rotating coil, crankshaft

Magnet, coil, oscilloscope

Faradays Flashlight


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How do power plants create AC power?

Faradays Law

Currents can be induced in wires by a

changing magnetic fields.

1. Move a magnet near a coil of wire

2. Move a coil near a magnet.


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How do power plants

move the magnet or coil?They are rotated on a shaft by

a water wheel in a hydroelectric dam

a large diesel engine or a gas turbine

But in most cases, the thing spinning thegenerator is a steam turbine.

The steam might be created by burning coal, oil ornatural gas. Or the steam may come from a nuclearreactor.


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How does a transformer work?

1. An AC current in the primary coil

creates a changing magnetic field in

the iron core.

2. This changing magnetic field

induces a current in the secondary

coil as described by Faradays Law.


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Transformers

3D Drawings (Cylinder and Block)

Circuit Symbol

Transformer Makers Equations

rms2

rms1

1

2

rms1

rms2

I

I

N

N

V

V


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What is a step-up transformer?

1N

N

V

V

1

2

rms1

rms2

What is a step-down transformer?

1N

N

V

V

1

2

rms1

rms2


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Center-tap Transformer


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How does a jumping ring work?

Lenzs Law

The induced currents in a conductor arein such a direction as to oppose the

change in magnetic field that producesthem..

Demo - RefrigeratorDraw Picture


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How does and inductor impede current?

Lenzs Law

The induced currents in a conductor are

in such a direct ion as to oppose the

change in magnet ic f ield that produces

them..

?


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How do you calculate inductance?

L = Inductance in HenriesN = Number of Turns

= Length of the Core

A = Area of the Core

m= Permeability of the Core =mrm

o

mo= 4p 10-7 H/m

Applications: Stoplight Car Detectors and Metal Detectors

2ANL

m


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Amperes Law Examples

Find the magnetic field strength for each of

the following:

1. Example 15.1 - A Long Straight Wire

2. Example 15.2 - A Toroidal Coil

3. Solenoid

m ildB


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Did we do these Demos?

Break a Trans former

Cool the Jumping Ring

Open a DC Power Supp ly

Inves tigate a Tes la Coil

Dr. Ts Faradays Law Demo

2 spr ing s, 2 magnets, 2 coi ls

Moving a wire in a magnetic f ield


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Chapter 16

DC Machines


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Just the basics

Electric Motor

Stator

Stationary part

Rotor Rotation part connect to a shaft

What role does a brush play in a motor?

Answer: Changes the direction of the current with the help

of a commutator.


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The Fundamentals of Engineering

Examination

Becoming a Professional Engineer (PE)

PE Examination for PE License

One goal of this course is to supply you withenough knowledge to pass the PE Exam.

See Appendix C for an example.

Some of these questions will appear on the final

exam in a modified form.


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Take Home Demo

Zip Lock Bags

Write Names on Bags

Include Printed Instructions

Disk Magnet

D Cell Battery

Screw

Paperclips

Rubber Bands

6 Wire with Plastic Insulation

30cm Wire with Varnish

15-Chapter 15 - Transformers

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Transcript of 15-Chapter 15 - Transformers