Experiment 8: Electromagnetic Induction
Introduction:
In 1831 Michael Faraday found that when a conductor moves through a magnetic
field (in a direction that the wire cuts across field lines) an electric potential difference
(voltage or emf) is induced in the conductor. In addition, if the conductor forms a closed
circuit, the induced voltage will produce an induced current.
You will move a conductor relative to a magnetic field and observe the resulting
induced voltages and currents. You will use a galvanometer to detect induced currents.
You will also investigate properties of using a wound coil (basically a generator) rather
than a single wire.
Procedure A: Induced current and the Galvanometer
1.
Connect both ends of a single white wire (the conductor you will use to induce
motional emf) to the galvanometer (recall this detects small currents).
2.
Using your right hand rules as needed and knowing the direction of the magnetic
field, predict which way the galvanometer will be deflected as you move the
conductor through the field so that the wire is surrounded by the magnet. Recall
as demonstrated in class, the galvanometer deflects to the right when positive
current enters the right terminal. Make a sketch that indicates the set up and your
predictions.
3.
Predict the deflection on the galvanometer as the wire is now pulled out of the
magnet.
4.
Now check the predictions by performing the experiment.
5.
Qualitatively examine the effects of pulling or pushing your wire faster. Discuss
your results and their relation to Faraday's law for motional emf.
Procedure B: Using a coil (a home built generator)
1.
Use a length of wire to make a coil with several turns or windings. Leave
sufficient leads to connect the coil to the galvanometer.
2.
Tape your coil to the table so that it is vertical (standing up). Then pick up the
magnet and rotate the magnet over the coil. Investigate what happens as you
move the magnet differently (experiment with speed and orientation).
3.
Investigate the effect of changing the number of coils N.
4.
Keep the number of coils the same as one of the previous experiments, but change
the size of the coils.
5.
Demonstrate at least one of your generators to your instructor and be able to
explain the qualitative results you have found.
Play with the tube and magnet up at the front desk. Also play with the paddles and large
magnet.