Experiment 8

Electromagnetic Induction

Objective:

 

The objective of this experiment is to qualitatively examine magnetic induction.

 

Equipment:

 

Two solenoids, two ammeters, an iron core, a power source, and connecting wires       

 

Theory:

 

Electromagnetic induction takes place when a current is generated in a coil of wire as a result of change in magnetic flux through the coil.  Magnetic flux , φm , of field B through a loop of area A, when B makes an angle of θ with respect to the direction normal to the area, is given by φm = BAcosθ.

 

 

 

 

If any or a combination of N, B, A, or θ changes with time, it induces an electromotive force (emf) E across the coil that is equal to

 

 

 

Procedure:

 

The procedure is to move a relatively strong bar-magnet in front of an induction coil and measure an estimate of the induced voltage in the induction coil with a galvanometer (G).  Instead of a strong bar-magnet, a second coil may be utilized; however, this coil must be fed by a current source to produce a magnetic field.  Perform the following cases:

 

A)    With a current of 2 A in the 2nd coil, move it toward the induction coil while inserting it in the induction coil, and record the direction and extent that the galvanometer deviates from zero.  Do this step once for slow motion and one for fast motion.

 

Note that if the 2nd coil is given a back-and-forth motion inside the induction coil (something close to a perfect oscillatory motion), the galvanometer needle keeps oscillating back-and-forth about its zero position.  Doing that, you are generating an alternating current, similar to the city electricity.

 

In Part A, the purpose is to just insert the 2nd coil into the induction coil and bring it to a stop in the coil, and record the direction of deviation of the needle of the galvanometer as well as the maximum reading, once for a slow motion and once for a fast motion. 

 

B)     With the 2nd coil inserted in the induction coil, pull it out once slowly and once fast and record the direction of deviation and reading of the galvanometer each time.

 

C)    Increase the current through the 2nd coil to 5 A and repeat Parts A and B.

 

 

D)    Repeat Parts A, B, and C with a much stronger magnet.  To make a much stronger magnet, insert an iron core inside the 2nd coil.  Make sure you keep the position of the iron core (a steel slender rod) fixed and centered with respect to the 2nd coil by inserting a piece of folded paper in between the rod and the 2nd coil.

 

You may record the results of your observations in a table similar to the one shown on the next page.

 

Answer the following questions after filling in the table as directed above:

 

1) What will happen to the results if you change the direction of current in the 2nd coil?

 

2) What will happen to the results if you reverse the wire connections to the galvanometer?

 

3) What will happen to the results if you do both (1) and (2) above at the same time?

 

  

 

Magnetic Induction

Chart

Without Iron Core

(Weak Magnet)

With Iron Core

in the 2nd coil (Strong Magnet)

 

Galvanometer Reading

 

Deviation

( + ) or ( - )

 

Galvanometer Reading

 

Deviation

( + )  or ( - )

 

 

Low

Current

 

 

Slow

In

 

 

 

 

Slow

Out

 

 

 

 

Fast

In

 

 

 

 

Fast

Out

 

 

 

 

 

 

High

Current

 

 

Slow

In

 

 

 

 

Slow

Out

 

 

 

 

Fast

In

 

 

 

 

Fast

Out

 

 

 

 

 

Data:

          Given:              Low Current:  2 A to 3 A,   high Current:  5 A to 7 A        

             

             Measured:      Fill in the chart.

 

Calculations:  N/A

 

Comparison of the Results:  Compare the values in the chart for different cases.

 

Conclusion:   To be explained by students.

 

Discussion:     To be explained by students.