Concepts of Physics

IIT JEE Physics (1978-2018: 41 Years) Topic-wise Complete Solutions

Attraction/ Repulsion of Parallel Coils


It is known that currents attract each other and antiparallel currents repel. In this experiment you will demonstrate these facts.


A DC power supply, three coils suspended from a base with an arrangement to pass currents in these.


Two Coils

  1. Remove connections from one of the outer coils and put it aside. So you have two coils suspended from the base.
  2. Connect the wires in the base so as to pass currents in the two coils in the same sense and see whether the coils go away from each other or they stick to each other.
  3. Now with your finger, shift one coil in its plane so that the center of coil is in front of the periphery of the other. Keep this coil in this position while the other coil is free to move. Connect the clip. See whether the two coils go away from each other or they stick to each other. Explain your observations.
  4. Now reverse the connections of one of the two coils. Repeat steps 2 and 3. Explain your observations.

Three Coils

  1. Now connect all three coils to DC voltage source. Connect them in such a way that in the outer coils currents go in same direction and in the middle one it goes in the opposite sense. Connect the clips for 10-15 seconds. See how the middle coil oscillates, sometime in its own plane and sometimes perpendicular to the plane.
  2. Explain your observations.