Faraday’s Law – Genecon and Transformer Name ___________________
Materials:
I. Genecon, Differential Voltmeter, LabPro, Computer
II. Low Voltage AC Power Supply, Transformer Set, Voltmeter, Banana Leads
Overview:
In this lab we will further explore the phenomena associated with magnets and coils
of wire. A generator is a device which uses relative motion between wires and magnetic
fields. The voltage output of a DC generator such as the Genecon can be written as: V() =
0.707NBA. where  is the rotational rate of the coil in rad/s, N = #turns of wire on the
coil, B = strength of the magnetic field in tesla, and A = area around which the turns of
wire are wound.
I. The Genecon Generator
Safety: DO NOT ATTEMPT TO PRODUCE MORE THAN 6.0 VOLTS AT ANY TIME.
► Connect the Diff. Voltage Probe to the LabPro and to the computer. Turn on the
computer and start Vernier. You should get a screen with Voltage on the vertical axis and
time on the horizontal axis. Connect the Genecon to the Diff. Voltage Probes. Start Data
Collection. Use your Genecon to produce about 4.0 volts as steadily as you can. Start
timing a 30 second time-period and count the total number of turns of the handle while
supplying about 4V. Highlight a region where the voltage is pretty constant. Click the Stat
Function to measure the average voltage and the time period.
Number of turns of handle = _______________ in 30 seconds time
Average Voltage Output = ______________ volts
f = frequency = (Number of turns of handle)/30s = ____________________ rev/s
 = angular speed in rad/s = 2f = _____________________ rad/s
► The gears of the Genecon amplify the rotational speed of the generator wires by a factor
of 48 times over the rotational speed of the crank. Thus actual = 48. If we assume that the
Genecon has coil-area 1.0 cm2 in a field of 0.25 tesla, calculate the number of turns of wire
on the coil inside the Genecon using V = 0.707NBAactual. Show work.
CYP labs
II. Transformers
Introduction:
Transformers transform one ac signal into another ac signal through a shared
electromagnetic wave interaction. The changing magnetic flux of the driven primary circuit
induces a current in the secondary passive circuit. If 100% of the changing magnetic flux is
shared by both circuits, then Faraday’s Law allows us to write:
Vp
Np

( BA) Vs

t
Ns
where Vp and Np are the voltage and number of turns on the primary circuit, and Vs and
Ns are the corresponding voltage and number of turns in the secondary circuit.
In reality, only a portion of the magnetic flux will be shared by the secondary circuit. We
will call this portion the efficiency of the transformer, and use the equation:
(1)
Vs V p

 efficiency . We will explore this relationship experimentally in this lab.
Ns N p
Procedure:
1. With the power supply off, connect AC output of the power supply to one of the 400 turn
coils. Connect one voltmeter in 200V ac~ mode to the secondary coil and one voltmeter in
200V ac~ mode to the power supply.
2. Set the power supply to the 6 volt ac voltage setting. Turn on the power supply.
3. Read the power supply voltage and the secondary voltage on the Voltmeters, and record
in the table.
4. Turn down the voltage and exchange your secondary coil with the coil with the next
higher number of turns. Repeat for the remaining configurations. Complete the remaining
calculations in the table.
Np
Ns
Ns / N p
Vp
Vs
Vs / V p
Vs / V p
Ns / N p
400
400
400
200
400
800
400
1600
200
3200
► Use your collected data to calculate the efficiency of your transformer when the input
side was 200 turns and the output side was 3200 turns.
General Summing Up Questions:
► A generator consists of 2100 turns of wire around a coil of area 100cm2. Calculate the
DC output voltage of this generator when operating at 60 cycles/second in a 0.33 tesla
field.
► A transformer has an efficiency of 80%. How many turns would have to be on the
secondary coil to achieve a voltage of 2400V if the primary coil has 500 turns and the input
voltage is 120V? Show formulas and work.
► A student wants to create a 6.0V AA “battery” from a 1.5V AA battery. Can the student
do this using an 80% efficient transformer? If so, give an example transformer coil ratio. If
not, why not?