Electromagnetic Induction
PRE LAB
Using an arrow show the direction of the induced current through the resistor R when the permanent
magnet is moved away from the coil.
N
S
R
The conductive rod in contact with both
rails is moving from L to R with speed
V. Using arrows, show the direction of
the current in both resistors. The
magnetic field, B, is normal to the sheet
coming out of the plane.
R1
R2
Electromagnetic Induction
PARTS LIST
PART
500 and 1000 turns
coils
QUANTITY
1 ea.
Transformer
1
Signal Generator
(Also called function
generator0
I-V probe
1
Lab Pro ULI
1
Power Supply
1
Multimeter
1
Compass
Permanent Magnet
Rods of various
materials
Wires, A-B
1
1
1ea.
2 sets
Electromagnetic Induction
PART I, Right Hand Rule
We will use the R.H.R. to find the winding direction of two Coils, one with 1000 turns and the others
with 500 turns. After determining the winding direction, check your answer with other groups. Results
of the remaining experiment depend on the direction of the windings.
Connect the 500-turns coil to the power supply, as
shown in the diagram. Make sure that port I is
connected to + and port II is connected to
negative terminals of the power supply. Turn on
the supply and apply approximately 0.7 volts to
the coil. Using the compass, determine the
direction of the induced magnetic field in the coil.
To do so, bring the compass close to one end of
the coil and notice the direction of the needle. If
you place the compass at the other end of the coil,
the direction of the needle should get reversed.
Use R.H.R to determine the direction of current
and the winding direction of the coil. Write your
answer (Figure A or B) in the data sheet. Repeat
the procedure for the coil with 1000-turns. The
windings for both coils are in the same direction.
II
I
500 turns coil
PART II, Lenz law, A
Connect the 1000-turns coil to the current probe of the ULI (+ to II and – to I). Note how the arrow on
the current sensor shows a positive measurement for a positive current from I to II. Start Logger Pro
with a blank file. If necessary, use Experiment-Connect Interface-Lab Pro if the interface is not
connected. Use Experiment-Set Up Sensors-Show all Interfaces to activate channel 1 and select
“current probe”. Use Experiment-Data Collection to increase the sample rate to 250 samples/second.
To get familiarized with the setup, take a permanent magnet and move its N pole in and out of the coil in
such a way that it produces an almost sinusoidal current waveform. Use right & left hand rules to predict
the induced current caused by decreasing and increasing the magnetic flux for the outlined in Table I of
the data sheet. Do the experiment and write the correct answer in that table. You will not be penalized
for incorrect predictions so do not alter your initial answers to the predictions.
PART II, Lenz law, B
Place the two coils facing each other, as
shown in the diagram. Connect the power
supply to the 1000-turns coil and connect
the current probe to the 500-turns coil.
Insert the laminated rod with the square
cross section between the two coils. This
will direct the magnetic field from one coil
to another coil. Make sure that the polarity
of the supply and the current probe matches
the polarities in the diagram.
+
II
1000 turns
I
II
500 turns
-
I
Turn on the power supply and crank the amplitude to the max. The current limiter will activate to limit
the voltage & current delivered. Reduce the voltage knob until the meter is lower than the maximum (so
the current limiter not in play).
Use right hand rule, the current direction, and the windings direction to predict the flux direction in the
supply coil. When suddenly disconnected (pull the banana plug out), the flux will decrease to zero. Use
right hand rule and the windings direction to predict the current induced in the 2nd coil. Check your
answers by experimenting. Record your answers in Table II.
PART III, Magnetic properties of materials.
As stated in Part II, the function of the
laminated “core” rod is to direct the
magnetic field generated in 1000-turns coil
into the 500-turns coil. Without the core,
less than 1% of the magnetic flux in the
primary will pass through the secondary.
With the core, about 5% of the flux passes
through the secondary. Supply the 1000
turn coil with the AC signal generator set at
f=10 Hz. Use the multimeter to measure the
voltage in the secondary and primary. Place
rods of various materials listed in Table III
between the two coils and measure the
voltage across the 500-turns coil. Based on
your measured voltages, decide if the
various materials are soft ferromagnetic or
not (able to augment field in both
directions).
+
-
II
I
1000 turns
II
I
500 turns
PART IV, Transformer
Make a transformer from two coils (see picture in the parts list) and connect the 500-turns coil to the
signal generator. Using the multimeter, measure and record RMS voltages for the primary and
secondary coils. Repeat the process for various input voltages. Compute the voltage ratios and answer
the final question.
Electromagnetic Induction
DATA SHEET
NAMES:
Part I: Which diagram represents the
correct winding direction from the
coils? (A or B?)
Your Answer:
II
Part IIA, Table I
N pole
facing side I
N pole
facing side II
S pole facing
side I
S pole facing
side II
I
II
Fig. A
C
Fig.
Fig. B
Action
Magnet is moved into coil
Magnet stationary inside the coil
Magnet is moved out of the coil
Magnet is moved into coil
Magnet stationary inside the coil
Magnet is moved out of the coil
Magnet is moved into coil
Magnet stationary inside the coil
Magnet is moved out of the coil
Magnet is moved into coil
Magnet stationary inside the coil
Magnet is moved out of the coil
Prediction (+, 0 or – current)
I
Experiment (+, 0 or – current)
Part IIB, Table II
Prediction (+, 0 or -)
Experiment (+, 0 or -)
Source on, plugs connected, DC current flowing
Source on, red plug suddenly pulled out
Source on, plug left out, no current flowing
Source on, red plug suddenly inserted
Part III, Table III
Voltage across 1st coil,
Vpri (volts RMS)
Voltage across 2nd coil,
Vsec (volts RMS)
Voltage Ratio
Vsec/Vpri
Air (no rod)
Laminated mild steel
Aluminum
Brass
Tool Steel
Plastic
Permanent Magnet
Mystery Metal
Part IV:
Trials Voltage across 500 turns coil Voltage across 1000 turns coil
Vpri (volts RMS)
Vsec (volts RMS)
1
2
3
4
For perfect magnetic coupling, what should the ratio be?
Voltage Ratio
Vsec/Vpri
Soft
Ferromagnetic
(Y or N)