what is the voltage across the split ring commutator when the loop is rotating?

lookang

Hero Member

Offline

Posts: 1796

http://weelookang.blogspot.com

1 what is the voltage across the split ring commutator when the loop is rotating?

Embed this message

on: November 03, 2009, 02:14:16 pm » posted from:Singapore,,Singapore

i am doing some research on java applet simulation on DC motor and AC generator.
http://www.walter-fendt.de/ph11e/generator_e.htm
show an interesting animation of the Dc voltage that resembled a full wave rectification. is that correct?
i thought it will be a constant voltage.

the reason is
i am trying to create a Voltage vs time graph for http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1266 and i am puzzled what shape it will be like?

ohm law V =IR,
during closed circuit,
if I is constant, and R is a fixed quantity across the split ring, should V is constant?
during open circuit,
I = 0, imply V = V as it is the voltage of the battery
so is it a constant line of voltage V = battery emf?

or is the physics of electromagnetic induction at the loop more complex that and i forgot to consider?

thanks for reply Grin

Screen shot 2009-11-03 at PM 03.06.03.png (37.55 KB, 713x354 - viewed 1090 times.)
« Last Edit: November 03, 2009, 02:16:28 pm by lookang »	Logged

Fu-Kwun Hwang

Administrator
Hero Member

Offline

Posts: 3086

2 Re: what is the voltage across the split ring commutator when the loop is rotating?

Embed this message

Reply #1 on: November 03, 2009, 08:58:23 pm » posted from:Taipei,T\'ai-pei,Taiwan

I think the magnetic field is assumed to be uniform B=B₀.
The magnetic flux pass through the coil depends on the angle $\theta=\omega t$ ,
assume the coil rotate at constant angular velocity $\omega$ .
i.e. $\Psi=\int \vec{B}\cdot d\vec{s}= B A cos(\theta)=B A cos(\omega t)$
From Faraday's law, induced voltage $V= -\frac{d\Psi}{dt}= BA\omega \sin(\omega t)$
So the voltage is a sine wave (without commutator).


	Logged

lookang

Hero Member

Offline

Posts: 1796

http://weelookang.blogspot.com

3 Re: what is the voltage across the split ring commutator when the loop is rotating?

Embed this message

Reply #2 on: November 03, 2009, 09:33:34 pm » posted from:Singapore,,Singapore

Quote from: Fu-Kwun Hwang on November 03, 2009, 08:58:23 pm

i agree with the above analysis that AC generator (without commutator) the emf induced in the coil is a sine wave.

so is it that with a commutator, which flip the current in half cycle rotation, therefore emf induced in the coil will be a |sine| wave?

if that is true, then i understand why the emf induced is |sine| wave.

By the way,
i am certain http://hyperphysics.phy-astr.gsu.edu/HBASE/magnetic/motdct.html is accurate for torque vs time is a |sine| wave.


« Last Edit: November 03, 2009, 09:41:09 pm by lookang »	Logged

Fu-Kwun Hwang

Administrator
Hero Member

Offline

Posts: 3086

4 Re: what is the voltage across the split ring commutator when the loop is rotating?

Embed this message

Reply #3 on: November 03, 2009, 10:42:02 pm » posted from:Taipei,T\'ai-pei,Taiwan

Yes. The commutator flip the current in half cycle to keep the voltage always positive.

For DC motor, there must be a commutator to generate torque in the same direction, otherwise, the ring will not rotate contineously (it will be become an oscillator.)


	Logged

Newbie

Offline

Posts: 1

5 Re: what is the voltage across the split ring commutator when the loop is rotating?

Embed this message

Reply #4 on: March 05, 2010, 09:09:20 pm » posted from:,,Germany

The adress of Walter Fendt's applet has changed. Now, it's http://www.walter-fendt.de/ph14e/generator.htm On his page there are quite a few other very useful applets: http://www.walter-fendt.de/ph14e/


	Logged

Pages: [1] Go Up

Wisdom is to form a good attitude and a healthy lifestyle. ...Wisdom

« previous next »

Related Topics
	Subject	Started by	Replies	Views	Last post
	Current Loop in magnetic field (How motor works!) Electromagnetism	Fu-Kwun Hwang	11	47638	April 16, 2011, 09:19:33 am by Fu-Kwun Hwang
	A loop rotating in a magnetic field (How electric power generator works!) Electromagnetism	Fu-Kwun Hwang	5	57815	December 12, 2009, 11:46:40 am by Fu-Kwun Hwang
	Pattern for Newton's Ring Optics	Fu-Kwun Hwang	1	16660	February 14, 2010, 04:32:46 pm by Fu-Kwun Hwang
	A loop rotating in a magnetic field (How electric power generator works! electromagnetism	ahmedelshfie	7	8406	April 22, 2010, 05:19:06 pm by ahmedelshfie
	Magnet Falling Through Ring Model Simulations from other web sites	ahmedelshfie	0	5072	September 13, 2010, 06:02:09 pm by ahmedelshfie

	Author	Topic: what is the voltage across the split ring commutator when the loop is rotating? (Read 14961 times)
0 Members and 1 Guest are viewing this topic. Click to toggle author information(expand message area).