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 ?(t) = __6.2831*t___
When ? = 0o What is amount of magnetic flux ? 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 ? and the new ? reading. By calculating d(?)/ 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(?)/ dt, it is more suitable to use d(?1)/ dt = (?2 -?0) / ( 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 ? and d(?)/ dt.  Collect more data to fill in the table if need.


Suggest a relationship between emf ? and i current.


Change the input field ?(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 ?(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, ? of rotation by changing the input field ?(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 ? in relation to the positions of the coil, ? = 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 ? = 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, ?  (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