Current-Carrying Coils In Magnetic Fields

Landato, Janet            St. Viator High School
                          312 392-4050
                           

Objectives:

At the end of this exercise the student should be able to:

1. predict the direction of movement for the pointer of a home-made 
   galvanometer for a given current direction.

2. describe how the current-carrying coil exerts a force on the 
   magnet.

3. predict how the number of turns of wire in the rotating coil 
   influences the rotation speed of the motor.

4. describe why the DC motor works without an armature.

Apparatus needed:
                       
1.5 m of enameled copper wire, one 1.5 V battery, one film cannister, 
two paper clips, 4 large rubber bands, one flat magnet with a hole, one 
hair pin, two nails, one small piece of wood or pegboard, two alligator 
clips, one large plastic bag 

Recommended strategy:    

Each student takes a plastic bag with apparatus inside.  Teacher asks 
"How can this 'junk' be used to find out how a current-carrying coil is 
influenced by a magnetic field?"  After a short discussion, the teacher 
shows models of film-cannister galvanometers and DC motors.  Students 
are encouraged to construct their own models and try to discover: 
     How does the number of turns of wire on the loop or galvanometer 
change the behavior of the apparatus?
     Does the distance of the rotating coil to the magnet influence the 
speed of the coil? 
     Does the number of batteries change the speed?
     How does the direction of current through the coil influence the 
direction that the galvanometer swings? 
     The direction that the motor coil rotates? 
     Explain how the coil exerts a force on the moving magnet in the 
galvanometer. 
     What makes and breaks the circuit in the DC motor if there is no 
armature? 

Reference:
"The Electric Motor Challenge", Physics Teacher. March, l74 (1985).
"Improvement on the Electric Motor", Physics Teacher. May, 308 (1985).