The Electric Motor
Name_________________________
_________________________
_________________________
In this lab you will investigate the relationships between voltage, current,
resistance, and power for different configurations of an electromagnetic motor. Using
the multimeter, you will measure these parameters for each of your motor set-ups and
plot them on graphs, then answer questions about the investigation.
The CPO electric motor kit uses a spinning wheel which can hold up to twelve
small magnets. These magnets must be placed in alternating polarities in order for
your motor to function, so be sure that when you “build” each motor configuration they
are switched between north and south alternatively. Depending upon the number of
magnets, you will select an overlay wheel with the appropriate number of
transparent/opaque bands. When placing the overlay wheel upon your motor, you
must be sure to position the BORDER between transparent and opaque directly
straddling a magnet. This is because the alternating bands pass beneath the main
electromagnet, and trigger a light-switch that reverses the polarity of the main
electromagnet, ensuring that your motor will continue spinning.
Begin with a TWO-MAGNET motor set-up.




Place the magnets on opposite sides of the wheel, in alternating polarities: one
should be north-outward and the other should be south-outward.
Locate the TWO-MAGNET overlay wheel and place it over the magnets, making
sure that the borders straddle the magnets. Fasten the overlay wheel down with
the plastic nut.
Fasten the main electromagnet and connect the battery pack.
Press the red button to complete the circuit, and give your wheel a gentle spin.
It should rotate slowly but continuously.
To establish a base level for current and voltage, STOP the wheel while keeping the
circuit connected (someone may need to hold the wheel to prevent it from spinning.
Measure the voltage and current using your mutlimeter. Record these figures in the
space provided below.
Vstopped
_________________
Istopped
__________________
Now, beginning with your TWO-MAGNET motor, ALLOW the wheel to spin, and
measure the voltage and current. Use these values to calculate the RESISTANCE and
POWER USED by the motor.
Repeat this process for different motor configurations using increasing numbers of
magnets: 4, 6, 8, and 12. Record all data in the table below.
Number of
Magnets
Voltage
Current
Resistance
Power
Construct TWO GRAPHS:


Number of magnets vs. BOTH voltage and current
Number of magnets vs. BOTH resistance and power
Answer the following questions:
1) How does the “no-load” voltage of the battery pack (measured with the battery
pack UNCONNECTED to the motor) compare with the voltage when the battery pack is
connected and the motor is spinning? When the motor is stopped?
2) How does the motor’s voltage compare when it is connected and stopped to when it
is connected and spinning?
3) How does the current compare when the motor is connected and stopped to when it
is connected and running?
4) How does the number of magnets compare to the power used by the motor when it
is spinning?
5) How does the number of magnets compare to the resistance of the motor when it is
spinning?
6) When the motor is spinning, most of the power goes into overcoming friction and
adding kinetic energy to the wheel. Where does all this energy go when you are
preventing the wheel from spinning? Why might this become a problem?
7) How much power does your 10-magnet motor use compared to a 100-Watt light
bulb? Do a calculation showing how many motors could be run by the power used by a
100-Watt bulb.