OHM'S LAW






Anderson, Herbert D.       Hermann Raster Elementary School
P.O. Box 19391             Chicago, IL 60636
Chicago, IL 60619
1-312-651-4587 


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