Name:_______________________________Date:_______________Time:____________

Course:_________________
_______________________________________________________________________

A. Ohm's Law Circuit

Purpose: To investigate Ohm’s law and measure resistances.

Apparatus: Transformer (6 volt), rheostat (89 ohm), 6- connecting wires (banana plug), 2-alligator clips, 5-ohm resistor, 10-ohm resistor, light bulb, and 2- digital multi meters (DMM).

Theory: Georg Simon Ohm (1787-1854), a German physicist, discovered Ohm’s law in 1826. This is an experimental law. Valid for both alternating current (ac) and direct current (dc) circuits.

When you pass an electric current (I) through a resistance (R) there will be a an electric potential difference (V) created across the resistance.

Ohm’s law gives a relationship between V , I and R as follows.

V = I R

Units: V------> volt (v), I------> ampere (A), R-----> ohm or v/A

For ohmic resistances, V versus I is a linear relationship, and they have a constant resistance. Resistance can be calculated using the Ohm’s law, R = V/I. The slope of the V versus I, line will also give the resistance, R.

For non-ohmic resistances, V versus I is a non-linear relationship, and they have a varying resistance. The resistance at a particular point can be calculated using Ohm’s law, R = V/I, where V and I are the voltage and current at that point.

Electric power, P is given by the following equation:

                    Power = P = Voltage x Current.

In order to investigate Ohm's law you will construct a circuit and measure the current through and voltage across the following: 5-ohm resistor, 10-ohm resistor, and light bulb.


Circuit Diagram:

Caution: Leave the power cord unplugged.  Plug it in only after your circuit is checked by the instructor.


Procedure:

1. First connect the following in a series circuit as shown below:
    Transformer (T), Rheostat, DMM as Ammeter (A), and unknown R (5-ohm resistor). 
                Use COM and A on a 2A scale, for the Ammeter.

2. Now connect the second DMM across the unknown R as shown below. Use COM and V on a 20-v range.

3. Call the instructor to check the circuit. 

DATA:     Unknown resistance: 5-ohm resistor.

Set the current, measure the voltage, and then calculate R. (Include units for V & R)

Current, I (A)

Voltage, V(__)

Resistance, R(__)

0

0

XXXXXXXXX

0.05

-

-

0.10

-

-

0.15

-

-

0.20

-

-

0.25

-

-

0.30

-

-

0.35

-

-

0.40 - -
0.45 - -
0.50 - -

Look at the resistance values and predict the V versus I relationship for the 5-ohm resistor.

____________________________________________________________________

Plot V versus I, and determine the slope.  Slope = _________________________


DATA:     Unknown resistance: 10-ohm resistor.

Set the current, measure the voltage, and then calculate R. (Include units for V & R)

Current, I (A)

Voltage, V(__)

Resistance, R(__)

0

0

XXXXXXXXX

0.05

-

-

0.10

-

-

0.15

-

-

0.20

-

-

0.25

-

-

0.30

-

-

0.35

-

-

0.40 - -
0.45 - -
0.50 - -

Look at the resistance values and predict the V versus I relationship for the 10-ohm resistor.

____________________________________________________________________

Add this plot of V versus I, to the earlier graph and determine the slope.  Slope = __________________

Print a hard-copy.


DATA: Unknown resistance, LIGHT BULB.

Set the current, measure the voltage, and then calculate R & P. (Include units for V, R, and P)

Current, I (A)

Voltage, V(__)

Resistance, R(__)

Power, P(__)

0

0

XXXXXXXXXX

-

0.05

-

-

-

0.10

-

-

-

0.15

-

-

-

0.20

-

-

-

0.25

-

-

-

0.30

-

-

-

0.35

-

-

-

0.40

-

-

-

0.45

-

-

-

0.50

-

-

-

0.55

-

-

-

0.60 - - -

Look at the resistance values and predict the V versus I relationship for the light bulb. 

____________________________________________________________________

Plot V versus I, on a separate graph and print a hard-copy.

Conclusion:

 

 

 

 

 

 

 

B. Circuits with Resistors and Capacitors 

Purpose: To investigate various combinations of resistors and capacitors. 

Apparatus: Three resistors, 3 capacitors, circuit board, digital multimeter, and 2-banana plug wires w/alligator clip on one end.   

A. Resistors:

1. Determine the values of the three resistors using the resistor color code.                                                

2. Measure the values of the three resistors using the digital multimeter (DMM).

3. Observe the tolerance values and them in the data table. 

 

R1

R2

R3

From resistor color code      
From digital multi- meter      
Tolerance      

4. When two or more resistances are connected in series the equivalent resistance, R is give by;

                        

When two or more resistances are connected in parallel the equivalent resistance, R is give by;

                        

5. Connect the three resistors as shown below and measure the equivalent resistance.

6. Also calculate the equivalent resistance values using the DMM values for individual resistances.

Resistor combination

Resistance values

Measured Calculated
All in series    

 

All in parallel    

 

   
   
   

 

B. Capacitors:

When two or more capacitors are connected in series the equivalent capacitance, C is give by;

                

When two or more capacitors are connected in parallel the equivalent capacitance, C is give by;

                     Measured values: C1= _______       C2=_______    C3=_______

Capacitor combination

Capacitance values

Measured Calculated
All in series    

 

All in parallel