OHM'S LAW

Anderson, Herbert D. Hermann Raster Elementary School
Chicago, IL 60636

Objectives (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). Recommended Strategies 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 explain. 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 RESISTANCE VOLTAGE = CURRENT X RESISTANCE RESISTANCE = VOLTAGE CURRENT 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 calculated value. 9. Pupils will use math skills to solve selected problems using Ohm's Law
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