O level Syllabus
This helps students learn
explain how a current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by increasing
(i) the number of turns on the coil,
(ii) the current
discuss how this turning effect is used in the action of an electric motor
describe the action of a split-ring commutator in a two-pole, single-coil motor and the effect of winding the coil on to a soft-iron cylinder
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?
The current comes from the battery higher potential end and travels in a wire forming a closed circuit and travels back to the lower potential end of the battery. When ? = 0o current flows from the battery higher potential end, to the top brush, to the RED split ring, through the coil loop in order ABCD, back to BLUE split ring, bottom brush and lower potential end of the battery. What is the direction of the current flow in wire AB? What is the direction of the current flow in wire CD? using Fleming's left-hand rule, deduce the relative directions of force acting on i) AB ii) CD iii) BC iv) DA. hint: note that Fmag = I*B*L*sin(I&B) may be useful.
By taking moments about the axle PQ, consider the forces on AB and CD, deduce the direction of the torque and the motion if the coil loop was initially at rest (? = 0 deg/s). Select the suitable sliders of your choice and verify your hypothesis for 2 angles. Discuss with your partner what you have discovered. Ask your teacher if there are any problem/issues faced using this virtual lab.
Explain and show the equations involving T ( in earlier part of question), why the forces on wire BC and DA did not contribute to the calculation of rotating torque about axle PQ?
By considering the forces in the x direction for wire BC and DA, suggest what can happen to the coil loop if the forces are large enough. Suggest why it does not happen in terms of the properties of the wires in the coil loop.
Explain how a current-carrying coil in a magnetic field experiences a turning effect and that the effect is increased by increasing (i) the number of turns on the coil, (ii) the current (iii) increasing the magnitude of the external Bz field
After conducting some inquiry learning on the virtual DC motor model discuss how this turning effect is used in allowing the coil loop to rotate. 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.
Describe the action of a split-ring commutator in a two-pole magnet setup, single-coil motor. Suggest the effect adding a soft-iron cylinder in the winding the coil.
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 today!
This is a derived work to help students understanding DC motors especially the split ring purposes. Thanks to Fu-Kwun Hwang for his original codes! here http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=912.0
1 made n =3 to simplify the number of currents to eyeball
2 added battery wires brush + sign to give context of power of DC motor
3 mask a part of the coil to give the illusion of single coil instead of plane previously
4 design the focus to be on just the 2 sides of the coil which has the most force that powered the rotation of DC motor
5 created animated gif as well for wikipedia.com i hope
6 added angle cta from 0 to 360 ^o to give sense of orientation
7 added omega for degree/s
8 added alpha for degre/s^2
9 added logic for split ring angle cta1 and cta2 to provide the ctadoubledot only when the is contact with split ring
10 equation of motion to reflect the no contact part to be without the torque from the magnetic force
11 magnetic force on and off when contact on and off
12 force shown
13 added particles for battery side wires which the particles motion is always from + potential so some code need to be re-purposed.
14 n is 5 now, better look and feel
15 motion of particles on battery wires now stop if there is no closed loop of the electric circuit
16 motion of particles current and electron are correctly reflected after extensive learning and debugging
17 added current can be negative
18 redesigned the angular acceleration and force activation condition into 4 quadrants, divide and conquer, previous original model is without the split ring consideration/model
19 added texts PQ axle, ABCD coil contact XY for ease of verbalization of communicating ideas and hypothesis for learners
20 added description and exercises to complement the virtual lab
21 rectified a major design mistake which i created due to misinterpretation of the usage of variable "sign" and finally got it to work (move) in correct representation/convention even with electron particles by designing with my own logic of how it can be made to do the simulation according to my understanding of the physics involved.
22 created a new logic for negative current in the battery wire to reflect the convention adopted today in physics
23 made the split ring commutator rotate with the coil instead of the original stationary design to conform to textbook explanation and the flash animation below
20March 2010 thanks to Taha Mzoughi http://physci.kennesaw.edu/mzoughi/bio.shtm remixed model, i realized what enhancements can be done.
24 added Torque clockwise positive view from the default perspective
25 Added Inertia to demonstrate the difficulty in increasing the angular velocity over time
26 added step button to allow for closer observation by learners
17 june 2010
27 redo the coil group to be lines instead of a 3D plane because it is drawing the whole plane instead of the perimeter
28 made java syntax false to make the split ring appear, in Ejs 4.3 default is true which the ring didn't show up
29 added simple 3D and Java3D optional from http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=1830
30 submit bugs to http://www.um.es/fem/EjsWiki/Feedback/Feedback?xsort=%E2%80%94created
31 leave the old version at top post and posted a underdevelopment proto-type at the bottom of post
11 feb 2011
added a new version DCmotor4 at the bottom post in order not to delete good version in case need to revert version
made beta split ring same color teal as the slider
made time slider
adjust the Bz drawing
made + bigger
change color of coil to DARKGRAY, the magnet blue and red is rather confusing with old color scheme
17 April 2011 (Saturday going Sunday at midnight after thinking about it every moment for a saturday)
major break through in bug fix now electron/current + splitring/ or without all bugs fix
added show graph angle, magnetic force, magnetic torque vs time and angle included even with data analysis
add N number of turns in coil
add lengthx as slider with all associated drawing of the particles
add lengthz as slider
fix a bug in evolution page domega/dt = (getAlpha(cta) -bf*omega)/Inertia where getAlpha(cta) is magnetic torque a2*Math.abs(Math.cos(cta)) where a2 = a2=N*I*B*L*b*1;
new assumption in sim is inertia is not affect by N, each slider controller is for conceptual exploration, not exactly mimicking real equipment so to speak.
26 April 2011
added more text battery brush split ring coil to situate the association of the drawings more clearly labels? will deactivate them
F drawn shorter now
added axes a powerful feature to allow sim to display in XYZ to XZY so that it is immediately the same setup as some textbooks and internet graphics
added decoration = axes as suggested by collaborator Sim KS
added worksheet is jar itself for scalability as lesser chance of losing curriculum material to accompany the simulation
added angle drawn theta with checkbox
added checkbox to show hide the magnets for printing the 3 view front side and top
03 May 2011
add Bcorrect to get the correct direction for the Z , using Bcorrect = -B;
made the text black for clearly print out
background made lighter for clearly print out
re-orientate the sim to be more textbook example like customize to O level
redesign the worksheet
08 July 2011
fixed a bug with B and Bcorrect after a sharing that i realized the left hand rule should be correct now.