[b]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

Exercises:
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.