Elenco Snaptricity® - Manual (Page 40)

5V
Project #30
1A
-39-
Educational Corner:
Ohm’s Law
Build the circuit as shown (leave the fan off the motor (M1).
Set the meter (M5) on the 1A setting, place the iron core
rod into the electromagnet (M3), and both slide switches
(S5) to the B position (off).
Assembly
Since the battery voltage is 4.5V, you can use Ohm’s
Law to calculate the resistance of each part:
Notes: Your actual results may vary. Unless your
batteries are new, the voltage may be less than 4.5V.
Also, your M5 meter is a simple meter. Don’t expect
it to be as accurate as normal electronic test
instruments. In some cases, the meter may show
zero current for the electromagnet; switch the meter
to the 1mA scale to prove a current is flowing.
Another problem is that the battery voltage drops a
little if the current is high. This drop may be 1-2 volts
for the motor with fan. For some motors, typical
resistance may be 3 ohms with fan and 20 ohms
without fan.
Optional: For a more accurate resistance
measurement, you can measure the actual voltage.
Place the meter across the battery holder, set it to
the 5V scale, and place a 3-snap wire where the
meter used to be. Use the switches to measure the
voltage for each part individually, as you did for the
current.
By comparing the currents you measured, you can see
which part has the most resistance to the flow of electricity.
Description
Voltage
Current
Resistance =
+
!
WARNING: Moving parts. Do not touch
the fan or motor during operation.
!
WARNING: Do not
lean over the motor.
1A
Operation
Set the left slide switch to position C to turn on the lamp (L4).
The meter measures the electric current through the lamp.
Set the left switch back to B and set the right slide switch to
position C. Now the meter measures the current through
the electromagnet. The electromagnet will attract the
compass needle.
Set the right slide switch back to B and push the press
switch (S2). Now the meter measures the current through
the motor.
Last, place the fan on the motor and measure its current
with the fan on.
Electric Paths
Voltage
Measured
Current
Measured
Resistance
Calculated
Typical
Resistance
Lamp 4.5 volts 15 ohms
Electromagnet 4.5 volts 30 ohms
Motor
(with fan)
4.5 volts 10 ohms
Motor
(without fan)
4.5 volts 40 ohms
FOR ADVANCED USERS - ADULT
SUPERVISION RECOMMENDED
4.5V
Current
=
+