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Author Topic: Ejs Open Source Alternating Current Generator Model Java Applet ( AC Generator )  (Read 18873 times)
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lookang
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on: October 29, 2009, 05:02:15 pm » posted from:SINGAPORE,SINGAPORE,SINGAPORE

Ejs Open Source Alternating Current Electrical Generator Model
AC generator applet
This model is created using open source physics and Easy Java Simulations (EJS) version 4.2 authoring and modeling tool. (Ejs) and the community using Ejs to enable inquiry learning.
The Alternating Current Electrical Generator Model was created by Fu-Kwun Hwang and lookang.
I would like to thank Fu-Kwun Hwang, Wolfgang Christian & Anne Cox for sharing their source codes so that i could learn and accelerate the creation of this learning environment.


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  • Post questions to be asked to help students to think, to explore.
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* acgenerator.png (74 KB, 1024x734 - viewed 298 times.)
« Last Edit: July 11, 2011, 01:49:17 pm by lookang » Logged
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Reply #1 on: November 03, 2009, 04:47:10 pm » posted from:Singapore,,Singapore

Alternating Current Electrical Generator Model

Electric generators turn motion into alternating-current electric power by exploiting electromagnetic induction. A loop that is placed in a magnetic field induces an motional electromagnetic force (emf). A simple alternating current (AC) generator is illustrated here. ABCD is mounted on an axle PQ. The ends of the wire of the loop are connected to 2 brushes contacting two slip rings continuously at position X & Y. Two carbon brushes are made to press lightly against the slip rings.

The motor features a external magnet (called the stator because it’s fixed in place) and an turning coil of wire called an armature ( rotor or coil, because it rotates). The armature induces an emf, because any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be "induced" in the coil.

The key to producing motional emf is in change in the magnetic flux experienced by the coil loop.

Faraday's law states the induced emf in a coil is equal to the negative of the rate of change of magnetic flux times the number of turns in the coil. The induced electromotive force or emf, ε in any closed circuit is equal to the rate of change of the magnetic flux , Φ through the circuit.

|ε| = | d(Φ)/ dt  |

where Φ = N.B.A cos ( B&A)

|ε|  is the magnitude of the electromotive force (emf) in volts

Φ is the magnetic flux through the circuit (in webers).

N is the number of turns of wire in the loop
B is the magnetic field

A is area of coil

angle B&A is the angle between vector magnetic field and vector perpendicular to the area


Lenz's law states an induced current is always in such a direction as to oppose the motion or change causing it.
The law provides a physical interpretation of the choice of sign in Faraday's law of induction, indicating that the induced emf and the change in flux have opposite signs. The the polarity of the induced emf is such that it produces a current whose magnetic field opposes the change which produces it

ε = - d(Φ)/ dt

For the case of a rotating loop,

ε = - d(Φ)/ dt

From eariler equstion as Φ = N.B.A cos ( B&A)

ε = - d(N.B.A cos ( B&A))/ dt

the physical setup of Bz and normal vector of area A when t = 0 s, such that angle B&A = ( θ + π/2 ).
and taking out the constants from the differential equation,

ε = - N.B.A d( cos ( θ + π/2 )/ dt

from mathematical trigometry identity, cos ( θ + π/2) = -sin ( θ  )

ε = - N.B.A d( -sin ( θ  )/ dt

To derive an expression for the induced emf across the slip rings when the coil is spun at a angular frequency, ω, knowing θ = ω.t

ε = - N.B.A d( -sin ( ω.t  )/ dt )

ε = N.B.A d( sin ( θ )/ dt )  which the equation used by the custom function  getCurrent () = d( sin ( θ )/ dt )
When a closed ciruit in connected to the rotating loop, using Ohm's law

ε =  N.B.A.d( sin ( θ )/ dt ) = I.R  which the equation used by the model

When mechanical energy is used to rotate the loop, the armature induced a emf described by the right hand rule. The induced emf in a coil is equal to the negative of the rate of change of magnetic flux times the number of turns in the coil.

Use the rotating handle function input field θ(t)= _________ to see what happens when the rotating handle cranks the loop in the Bz magnetic field. The checkbox current flow & electron flow alows different visualization since I = d(Q)/dt and Q= number of charge*e. The Play & Pause button allows freezing the 3D view for visualizing these induced currents, for checking for consistency with the right hand rule.

When the rotating handle is moved by the input field θ(t)= 2*t , induced current runs through ABCD (select the checkbox labels?) in a manner described by
ε =  N.B.A.ω .cos ( ω.t  ) = I.R.

since θ(t)= 2*t , imply 2 = ω

ε/R =  N.B.A.ω .cos ( ω.t  )/R = I. which is the modeled equation.

If N = 1, B = 2 x10-6 T, A = 1.5*1.5 m*m, R = 1 Ω

ε/R =  1.2.1.5*1.5.2x10-6 .cos ( 2.t  )/1 = I.

ε = 9x10-6 cos ( 2.t  ) = I




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« Last Edit: November 16, 2009, 04:21:47 pm by lookang » Logged
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Reply #2 on: November 09, 2009, 04:58:59 pm » posted from:SINGAPORE,SINGAPORE,SINGAPORE

Exercises:
There is an external magnet with the poles as setup in the z axis direction.
What are the magnetic poles when Bz is positive?.
Top:
Bottom:

What can you conclude about the directions of the magetic field exerted by the magnets? hint: the magnetic field vectors comes out from which pole when view from outside the magnet.

 
The external magnetic field Bz can be varied using the slider Bz. When Bz is positive, it is in the direction vertically up. Vary Bz until it is negative, what is the direction of the Bz then?


Input into the input field θ(t) = __6.2831*t___
When θ = 0o What is amount of magnetic flux Φ passing through the area of the coil loop is zero Wb? (can be visualized from the virtual lab as a gray area)
Step the simulation by dt, take note of the new value of the θ and the new Φ reading. By calculating d(Φ)/ dt, at this instant in time. Think of a way, to collect the data to fill in the following table.
The time step in the simulation can be taken to be dt = 0.05 s
Ask your teacher if there are any problem/issues faced using this virtual lab.

   
   
   
In the estimation of d(Φ)/ dt, it is more suitable to use d(Φ1)/ dt = (Φ2 -Φ0) / ( t2 - t0) , suggest a reason why?

Analyse the data and also select the Checkbox "Show Graph" the observe the graphs.
Suggest a relationship between emf ε and d(Φ)/ dt. Collect more data to fill in the table if need.


Suggest a relationship between emf ε and i current.


Change the input field θ(t) = __10*t___
By substituting t = 1.00 s or otherwise, suggest the meaning of the number 10 ? hint: You should explore changing the value of 10 to others values and record your observations.


From the topic of waves, the concept of period T is ___________________________________________________.
suggest how the 2 variables are related.


Show your working clearly,
What is 6 rotations / minute means in _____________________ rad/s.

key in the value calculated into the input field θ(t) = _____* t

Select the checkbox "Show graph". Select the checkbox "vs time" or otherwise, note and draw the shape of the graph of "induced emf" and "time".
















What is the galvanometer pointer measuring and in what units?


Select the checkbox "Current Flow". Observe the current motion. What the current flow direction that causes the a positive deflection in the galvanometer ?


Change the frequency of rotation to 12 rotations / min. Draw the 2 graphs together with labels of "induced emf" and "time" and describe the changes in the graph and the movement of the galvanometer pointer. State a reason for the changes that occur.











The following passage (just an example) aims to aid learners describe a simple form of a.c. generator (rotating coil or rotating magnet) and the use of slip rings (where needed)

When a coil is _______________ between the poles of the ___________, its wires cut through the _______________ causing an induced emf to be generate which causes a ____________ to flow if there is a closed electrical path ciruit.
The _________ and ______________ of the induced current _____________ as the coil rotates. This is the basic principle behind the simple AC generator.


Set the angular velocity, ω of rotation by changing the input field θ(t) = ____0____. The galvanometer shows no reading. Why?


Select the checkbox that toggle between "Current Flow" and "Electron Flow". Play the simulation for the same settings and suggest a relationship between current flow and electron flow. Tailor your explanation to i = d (Number of charge*q)/ dt




Select the checkbox "Show graph". Select the checkbox "vs angle" or otherwise, note the positions of the galvanometer pointer and the induced emf ε in relation to the positions of the coil, θ = 0 , 90 , 180 , 270, 360 etc. Redraw the graph of vs angle in relation to the actual setup with the magnetic field direction.











Answer the following questions: hint: use the pause button or step button to take observations and readings if the motion is too fast.
a) Click on the `Pause’ button to stop the movement of the coil when
the induced e.m.f. is zero.
i) What is the position of the coil relative to the magnetic field?


ii) Explain why the induced e.m.f. is zero when the coil is at this position.


b) Click on the `Pause’ button to stop the movement of the coil when
the induced e.m.f. is maximum.
i) What is the position of the coil relative to the magnetic field?

ii) Explain why the induced e.m.f. is maximum when the coil is at this position.
  
c) Click on the `Pause’ button to stop the movement of the coil when
the induced e.m.f. is minimum.
i) What is the position of the coil relative to the magnetic field?

ii) Explain why the induced e.m.f. is minimum when the coil is at this position.

Click on the `Pause’ button to stop the movement of the coil when it is in the vertical position say θ = 0. Use Fleming’s Right Hand Rule to check the directions of the induced current along the AB side and CD side of the coil. Discuss with your team mates how you use Fleming’s Right Hand Rule in relationship to the setup. Write down what you have learnt about Fleming’s Right Hand Rule used in this situation.




Note and state the direction of the current flowing through the external resistor, R.


Click on the `Play" button to start the movement of the coil.
Stop the movement of the coil when it is in the next vertical position after rotating through 180o.
Use Fleming’s Right Hand Rule to check the directions of the induced current along the AB side and CD side of the coil.
Note and state the direction of the current flowing through the external circuit (resistor). hint: you may need to manipulate the java applet to observe and trace the path of the current.



7 Complete the following statement(*delete where inapplicable):
The induced current flowing through the external circuit (resistor) is (*direct / alternating).

8 Suggest 3 other ways of increasing the induced e.m.f. in the coil.
hint: you may explore the purpose of Number of coils N, magnetic field strength Bz etc.



(c) sketch a graph of voltage output against time for a simple a.c. generator





Explain how a rotating coil in a magnetic field experiences a change in magnetic flux linkage and the induced emf. What is the effect on the induced emf by increasing (i) the number of turns on the coil, N (ii) the angular velocity, ω (iii) the magnitude of the external Bz field.


Describe the action of a commuator slip rings of the AC generator. Suggest the effect of adding a soft-iron cylinder in the winding the coil.

Calculate the value of the angular velocity of the AB coil when the lengthz = 0.5 m.





After conducting some inquiry learning and examining the 3D view of the model on the virtual AC generator model discuss how this induced emf can be measured. You may right-click within a plot, and select "Open EJS Model" from the pop-up menu to examine the model equations of the motion. You must, of course, have EJS installed on your computer.


Advanced Learner:
Please submit your remix model that model features that are not available in the existing virtual lab and share your model with the world through NTNUJAVA Virtual Physics Laboratory http://www.phy.ntnu.edu.tw/ntnujava/index.php?board=28.0. Impacting the world with your model now.


changes

1 added equations for flux from http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=915.0
2 made some adjustment to the equations to reflect the flux correctly http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=915.msg4942#msg4942
3 remove DC motor parts
4 added AC generator parts
5 adapted from the way the loop coil in drawn http://www.compadre.org/OSP/items/detail.cfm?ID=9218&Attached=1
6 adapted useful components of http://www.compadre.org/OSP/items/detail.cfm?ID=9218&Attached=1 like plot and the calculation for flux and current
7 re-adapt to the magnetic field B in z direction which took a lot of effort to rethink the physics laws
8 adjusted the equations to reflect the physics for my model
9 added new equation flux = NBA*cos(B&A) instead of the older equation
10 added N number of loops slider
11 added lengthx and lengthz slider to promote inquiry learning of physics phenomena
12 added the ammeter group from http://www.compadre.org/OSP/items/detail.cfm?ID=9218&Attached=1
13 customized the particles to work even with lengthx and lengthz
14 current particles motion particles velocity now are smaller for cases for N=7
15 modified equation to reflect the equation of induced emf = N*B*A* cos(B&A) = IR
16 direction of motion obeys v = omegas*lengthz/2;
17 particles in ABCD are good with proper initialization
18 moved the handle group to the other side to simulate handle being cranked
19 added resistor into the simulation
20 adding description
21 adding exercises
17 june 2010
22 read with error in E:\EJS_4.3.0_100613\EJS_4.3.0 but no error in E:\EJS_4.2.7_100314\EJS_4.2.7\
23 continuing improvement on  EJS_4.2.7_100314\EJS_4.2.7\
24 made the connection between rotating handle and coil match the length of the coil and lengthx changes
25 made width = 600 to fit blog post http://sgeducation.blogspot.com/2010/06/ejs-open-source-alternating-current.html
26 made some color scheme changes to background


to do
add flux,emf vs angle to plot
add visualization of flux on main drawing http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=915.msg3437#msg3437


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« Last Edit: June 17, 2010, 03:39:08 pm by lookang » Logged
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Reply #3 on: November 16, 2009, 04:22:19 pm » posted from:SINGAPORE,SINGAPORE,SINGAPORE

work in progress.

working from the DCmotor model

My experience tell me to stay with EJS_4.2_090719 cos EJS_4.2_091031 seems to take a long time for adding variables
D:\EasyJavaSimulation\EJS_4.2_090719\EJS_4.2

Possible Models
http://www.compadre.org/OSP/items/detail.cfm?ID=9218&Attached=1 written by Anne Cox and Wolfgang Christian
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=915.0 written by Fu-Kwun Hwang

Reference:
http://www.walter-fendt.de/ph11e/generator_e.htm by Walter Fendt
http://micro.magnet.fsu.edu/electromag/java/generator/ac.html by Michael W. Davidson
http://www.pbs.org/wgbh/amex/edison/sfeature/acdc_insideacgenerator.html by PBS Online


* ACgeneratooldr.PNG (26.73 KB, 700x585 - viewed 154 times.)

* acgenerator.png (74 KB, 1024x734 - viewed 712 times.)

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« Last Edit: April 28, 2010, 07:46:24 am by lookang » Logged
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Reply #4 on: July 26, 2010, 09:09:39 pm »

YouTube. Was stuck at Portland airport from 11pm to 4am, decided to use the time to make some promotional video on the applets shared during 2010 AAPT Summer Meeting in Portland, Oregon


Enjoy!

Attachment is the doc for the Branded Blended Learning (BBL): The TSOI Model for Electromagnetic Induction & its applications for
Transforming Science Instruction in Today’s “Classroom”


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« Last Edit: February 14, 2011, 03:01:58 pm by lookang » Logged
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Reply #5 on: February 25, 2011, 12:24:45 am » posted from:Singapore,,Singapore

update the AC generator applet but decide against over writing on the first post for fear of bugs still un resolved.

enjoy!

Embed a running copy of this simulation

Embed a running copy link(show simulation in a popuped window)
Full screen applet or Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list
Press the Alt key and the left mouse button to drag the applet off the browser and onto the desktop. This work is licensed under a Creative Commons Attribution 2.5 Taiwan License
  • Please feel free to post your ideas about how to use the simulation for better teaching and learning.
  • Post questions to be asked to help students to think, to explore.
  • Upload worksheets as attached files to share with more users.
Let's work together. We can help more users understand physics conceptually and enjoy the fun of learning physics!
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Reply #6 on: February 25, 2011, 12:43:27 am » posted from:Singapore,,Singapore

a new youtube to share

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