# NTNUJAVA Virtual Physics LaboratoryEnjoy the fun of physics with simulations! Backup site http://enjoy.phy.ntnu.edu.tw/ntnujava/

## Easy Java Simulations (2001- ) => Electromagnetism => Topic started by: Fu-Kwun Hwang on February 01, 2009, 04:32:40 pm

 Title: Current Loop in magnetic field (How motor works!) Post by: Fu-Kwun Hwang 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 (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1396.0) Title: Re: Current Loop in magnetic loop (How motor works!) Post by: Fu-Kwun Hwang on February 01, 2009, 11:16:43 pm 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-directionEven 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!) (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=915.0) Title: Re: Current Loop in magnetic loop (How motor works!) Post by: lookang on February 02, 2009, 07:58:33 am Quote from: Fu-Kwun Hwang on February 01, 2009, 04:32:40 pmThis 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 .Quote from: Fu-Kwun Hwang on February 01, 2009, 04:32:40 pmBecause 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! Title: Re: Current Loop in magnetic loop (How motor works!) Post by: Fu-Kwun Hwang 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) Title: Re: Current Loop in magnetic field (How motor works!) Post by: lookang on October 23, 2009, 12:36:18 pm 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.htmlhttp://www.walter-fendt.de/ph11e/electricmotor.htmi try to remix from your applets, i will learn a lot from remixing.will ask again for help Title: Re: Current Loop in magnetic field (How motor works!) Post by: lookang on October 29, 2009, 01:45:34 pm i am done remixing Ejs Open Source DC Motor Model by Fu-Kwun Hwang and lookanghttp://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1266enjoy 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(http://www.phy.ntnu.edu.tw/ntnujava/index.php?action=dlattach;topic=1266.0;attach=1432;image) (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1266[img) Title: Re: Current Loop in magnetic field (How motor works!) Post by: lookang on December 12, 2009, 12:26:45 am Hi prof hwang,[noeqn]found the second applet not loading like i encountered before.load: class users.ntnu.fkh.currentloopinbmotor_pkg.currentloopinbmotorApplet.class not found.java.lang.ClassNotFoundException: users.ntnu.fkh.currentloopinbmotor_pkg.currentloopinbmotorApplet.class   at sun.plugin2.applet.Applet2ClassLoader.findClass(Unknown Source)   at java.lang.ClassLoader.loadClass(Unknown Source)   at java.lang.ClassLoader.loadClass(Unknown Source)   at sun.plugin2.applet.Plugin2ClassLoader.loadCode(Unknown Source)   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 sun.plugin2.applet.Applet2ClassLoader\$1.run(Unknown Source)   at java.security.AccessController.doPrivileged(Native Method)   ... 7 moreException: java.lang.ClassNotFoundException: users.ntnu.fkh.currentloopinbmotor_pkg.currentloopinbmotorApplet.classReading 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 Title: Re: Current Loop in magnetic field (How motor works!) Post by: Fu-Kwun Hwang on December 12, 2009, 09:41:27 am Thank you! It is fixed now. Title: Re: Current Loop in magnetic field (How motor works!) Post by: macfamous on February 26, 2010, 01:11:08 am Sorry but I still get a little problem here .. may we have just a simple formula for this .. -*- Title: Re: Current Loop in magnetic field (How motor works!) Post by: Fu-Kwun Hwang on February 26, 2010, 11:03:49 am The fomula for force and torque are provided in the previous posts. May I know what kind of formula are you looking for? Title: Re: Current Loop in magnetic loop (How motor works!) Post by: lookang on April 15, 2011, 10:32:32 am Quote from: Fu-Kwun Hwang on February 01, 2009, 11:16:43 pmHere 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-directionEven 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!) (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=915.0)Hi Prof!i think i found a small bug that did not affect the simulation model because the inertia in your sim is always 1the logic isif dcta/dt = omegadomega/dt = (getAlpha(cta) -bf*omega)/Inertiabecause (getAlpha(cta) -bf*omega) = resultant torqueso 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 thisdcta/dt = omegadomega/dt = (getAlpha(cta) -bf*omega)/Inertiawhere a2=I*L*B*b; for your case, since your (or our) a2 is the torque*length bneed to modify code at 2 places. Title: Re: Current Loop in magnetic field (How motor works!) Post by: Fu-Kwun Hwang on April 16, 2011, 09:19:33 am It is corrected! I was tring to calculate torque and angular velocity.However, it was displayed as force and velocity.Thank you!