NTNUJAVA Virtual Physics LaboratoryEnjoy the fun of physics with simulations! Backup site http://enjoy.phy.ntnu.edu.tw/ntnujava/
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 Author Topic: Current Loop in magnetic field (How motor works!)  (Read 45561 times) 0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).
Fu-Kwun Hwang
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 « Embed this message on: February 01, 2009, 04:32:40 pm »

This simulation shows a current loop in uniform magnetic field.
The black arrows show the force due to magnetic field on the loop.
$\vec{F}= q \vec{v} \times \vec{B}$ or $\vec{F}= I \int d\vec{\ell} \times \vec{B}$
The magnetic field in in the +Z direction if Bz>0.
Then ,torque for the loop is calculated from definition $\vec{\tau}=\vec{r}\times\vec{F}$

Because the current flow in the same counter-clockwise direction.
The force on the loop change sign during each helf cycle.
If we current reverse direction during each helf cycle, the following device can turn into a motor.
A voltage source is needed in the loop to drive the current.
-*-

P.S. The above simulation did not include the induced emf due to changing magnetic field in the loop.

You are welcomed to check out a very good animation DC motor operation principle

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Fu-Kwun Hwang
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 « Embed this message Reply #1 on: February 01, 2009, 11:16:43 pm »

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Here is the real motor:

In order to make motor reach stable rotational motion. A friction force is introduced: F=-constant *b*omage;//where b is the width in y-direction
Even thought magnitude of the magnetic force is the same (black arrows),
the torque is a function of cos(w*t)

If the process is reversed: A loop rotating in a uniform magnetic field will become electric power generator.
Please check out A loop rotating in a magnetic field (How electric power generator works!)

Registed user can get files related to this applet for offline access.
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Embed a running copy of this simulation

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Full screen applet or Problem viewing java?Add http://www.phy.ntnu.edu.tw/ to exception site list
• 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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lookang
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http://weelookang.blogspot.com

 « Embed this message Reply #2 on: February 02, 2009, 07:58:33 am » posted from:SINGAPORE,SINGAPORE,SINGAPORE

This simulation shows a current loop in uniform magnetic field.The magnetic field in in the +Z direction if Bz>0.
1. Add vector field arrow(s) for vector Bz .

Because the current flow in the same counter-clockwise direction.

2. Add  arrow(s) line along the sides of the wires to aid visualization of I current and q current flow.
$\vec{F}= q \vec{v} \times \vec{B}$ or $\vec{F}= I \int d\vec{\ell} \times \vec{B}$

3. in the electron objects, can draw a negative sign -, to make it immediately association to electrons?

indeed  nice applets
can split posts into 2 separate applets for ease of discussion/collaboration etc.

thanks!
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Fu-Kwun Hwang
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 « Embed this message Reply #3 on: February 02, 2009, 09:59:13 am »

I modified it according to your suggestion. However, I did not draw negative sign, because there are too many symbol shown already.
More checkboxs are added for user to decide which symbols s/he did not need! (velocity/field/force)
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lookang
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 « Embed this message Reply #4 on: October 23, 2009, 12:36:18 pm » posted from:SINGAPORE,SINGAPORE,SINGAPORE

i found these applets that can be referred to for improving the Ejs applet above.

http://www.magnet.fsu.edu/education/tutorials/java/dcmotor/index.html

http://www.walter-fendt.de/ph11e/electricmotor.htm

i try to remix from your applets, i will learn a lot from remixing.

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lookang
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 « Embed this message Reply #5 on: October 29, 2009, 01:45:34 pm » posted from:SINGAPORE,SINGAPORE,SINGAPORE

i am done remixing Ejs Open Source DC Motor Model by Fu-Kwun Hwang and lookang
http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1266
enjoy and thanks again Prof Hwang!

http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=1266.0;attach=1432;image[/img]]http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1266
 « Last Edit: October 29, 2009, 01:47:17 pm by lookang » Logged
lookang
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 « Embed this message Reply #6 on: December 12, 2009, 12:26:45 am » posted from:Singapore,,Singapore

Hi prof hwang,
java.lang.ClassNotFoundException: users.ntnu.fkh.currentloopinbmotor_pkg.currentloopinbmotorApplet.class
at sun.plugin2.applet.Plugin2Manager.createApplet(Unknown Source)
at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source) at java.lang.Thread.run(Unknown Source) Caused by: java.io.IOException: open HTTP connection failed:http://www.phy.ntnu.edu.tw/ntnujava/ejs4/users/ntnu/fkh/currentloopinbmotor_pkg/currentloopinbmotorApplet/class.class at sun.plugin2.applet.Applet2ClassLoader.getBytes(Unknown Source) at sun.plugin2.applet.Applet2ClassLoader.access$000(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
... 7 more
Exception: java.lang.ClassNotFoundException: users.ntnu.fkh.currentloopinbmotor_pkg.currentloopinbmotorApplet.class
Reading certificates from 11 http://www.phy.ntnu.edu.tw/ntnujava/ejsuser/14019/ejs_DCmotor.jar | C:\Users\160\AppData\LocalLow\Sun\Java\Deployment\cache\6.0\21\48384655-45e7ddf6.idx
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Fu-Kwun Hwang
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 « Embed this message Reply #7 on: December 12, 2009, 09:41:27 am » posted from:Taipei,T\'ai-pei,Taiwan

Thank you! It is fixed now.
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macfamous
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 « Embed this message Reply #8 on: February 26, 2010, 01:11:08 am » posted from:Yogyakarta,Yogyakarta,Indonesia

Sorry but I still get a little problem here .. may we have just a simple formula for this .. -*-
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Fu-Kwun Hwang
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 « Embed this message Reply #9 on: February 26, 2010, 11:03:49 am » posted from:Taipei,T\'ai-pei,Taiwan

The fomula for force and torque are provided in the previous posts.
May I know what kind of formula are you looking for?
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lookang
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 « Embed this message Reply #10 on: April 15, 2011, 10:32:32 am » posted from:SINGAPORE,SINGAPORE,SINGAPORE

Here is the real motor:

In order to make motor reach stable rotational motion. A friction force is introduced: F=-constant *b*omage;//where b is the width in y-direction
Even thought magnitude of the magnetic force is the same (black arrows),
the torque is a function of cos(w*t)

<applet code="users.ntnu.fkh.currentloopinbmotor_pkg.currentloopinbmotorApplet.class" codebase="/ntnujava/ejs4/" archive="ejs_currentloopinbmotor.jar" name="currentloopinbmotor" id="currentloopinbmotor" width="626" height="628"></applet>

If the process is reversed: A loop rotating in a uniform magnetic field will become electric power generator.
Please check out A loop rotating in a magnetic field (How electric power generator works!)

Hi Prof!
i think i found a small bug that did not affect the simulation model because the inertia in your sim is always 1

the logic is
if
dcta/dt = omega

domega/dt = (getAlpha(cta) -bf*omega)/Inertia

because (getAlpha(cta) -bf*omega) = resultant torque

so magnetic torque = getAlpha(cta)
and magnetic force is F= N*I*L*B*sign2;

the a2 is actual the a2=N*I*L*B*b; (in my DC sim Ejs Open Source DC Motor Model by Fu-Kwun Hwang and lookang http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1266) instead of a2=I*L*B*b/Inertia (in your current DC sim http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=912.msg3432#msg3432;
ignore my N because i have modified the sim into a multi turns DC motor.

is my interpretation of the physics DC model correct?
thanks!

In other words,
your model should be like this
dcta/dt = omega
domega/dt = (getAlpha(cta) -bf*omega)/Inertia
where a2=I*L*B*b; for your case, since your (or our) a2 is the torque*length b
need to modify code at 2 places.
 « Last Edit: April 15, 2011, 10:40:06 am by lookang » Logged
Fu-Kwun Hwang
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 « Embed this message Reply #11 on: April 16, 2011, 09:19:33 am » posted from:Taipei,T'ai-pei,Taiwan

It is corrected!
I was tring to calculate torque and angular velocity.
However, it was displayed as force and velocity.
Thank you!
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"That their main business was not put into the mind knowledge which was not there before, but to turn the mind's eye towards light so that it might see for itself." ...Plato's advice to educators(429-347BC)