Return to Physics Index
Anderson, Herbert D. Hermann Raster Elementary School
Chicago, IL 60636
(a) to become aware of Ohm's Law, the relationship between current, voltage, and
resistance in a series circuit
(b) to solve selected problems using Ohm's Law
Equipment and Materials
Garden hose with nozzle; circuit board or plywood; 3 - 1.5 Volt DC batteries; 6
battery clips & 3 battery holders (not needed if hobby batteries are used); 2- 4.5 V
bulbs; l variable resistor (the one used was 25 Ohms 2 Watts); bell wire; screw
driver; 2 lamp sockets; multimeter (optional).
1. Review basic laws of electrostatics and conductivity. Also, review schematic
diagrams of simple circuits.
2. Use the garden hose to demonstrate the analogy of water pressure with voltage,
drops of water with electrons, flow of water with electrical current, resistance
of hose and nozzle with resistance in a circuit etc.. During discussion,
introduce key vocabulary terms: AMPERE; VOLTS; OHMS; RESISTANCE; CURRENT
3. Connect one, then two, and finally three 1.5 volt dry cells in a series circuit
to a socket with a 4.5 volt bulb. The pupils will observe and explain the
varying degree of brightness of the bulb with respect to the increased voltage
and the increased current.
4. Connect 3 - 1.5 volt dry cells in series to both sockets, using 4.5 volt bulbs.
The pupils will notice the bulbs' brightness as compared to using one or two dry
cells. The pupils will explain.
5. Insert the variable resistor into the circuit [You will have to connect the
negative terminal to the center terminal with a clip], using 3 dry cells to one
socket with a 4.5 volt bulb. The pupils will vary the resistance from the least
resistance to where the bulb will not light. The pupils will observe and
6. Through discussion, the class will realize the relationship between current,
voltage, and resistance (Noting that this is for D.C. current only).
7. Introduce the pupils to OHM'S LAW : CURRENT = VOLTAGE
VOLTAGE = CURRENT X RESISTANCE RESISTANCE = VOLTAGE
Current is measured in Amperes; Voltage is measured in Volts; Resistance is
measured in Ohms.
8. If available, use a multimeter to measure the current and voltage in the circuit,
then calculate the resistance. Now, measure the resistance and compare to the
9. Pupils will use math skills to solve selected problems using Ohm's Law