Experiment 3: Ohm’s Law                                                                    Date: 22.03.2004

Objective: 1) To investigate the relationship between the variables V, R, and I in an

                      electric circuit.

                  2) To analyze series and parallel connection in terms of V, R, I

                  3) To determine the relationship between current and voltage in a circuit that  

                      contain a filament bulb

Theory:

It is known that electrons flow through a conductor metal wires with an ease without any resistance. This means that nothing would prevent the flow of the electrons. In a normal case however, under normal conditions, a resistance in the wire would affect the flow of the electrons in much the same way that friction slows down a sliding box on a platform. To allow more electrons to move against the resistance of a wire, it is necessary to apply a potential difference between the two ends. One can calculate the potential difference needed to create a current, I if the constant resistance, R of the wire is known. The relationship between these three variables (R, I, V) is given through Ohm’s Law which stated that the potential difference, V in a wire is proportional to the current, I if the temperature and all other physical quantities are fixed. From the law itself, we have an expression:

V=IR

6. The resistor is remove the next one used is chosen. The voltage is recorded in Table 1 as in step 5. The process is continued until all the resistors’ voltage recorded.

Part 2: Resistance in circuits  

1. Three resistor of the same value is chosen. The set of colours is recorded in Table 2.
2. The coded value of the resistors is determined and the value is recorded in the column labelled “Coded Resistance” in table 2. The tolerance value is entered as indicated by the colour of the fourth band under “tolerance”
3. The multimetre is used to measure the resistance of the three resistors. The value is then recorded in Table 2.
4. The percentage experimental error for each resistance value is calculated and is recorded
5. The three resistors are connected to the series circuit by using the spring clips on the Circuit Experimental Board to hold the leads of resistors together without bending them. The resistance of the combination is measured as indicated on the diagram by connecting the leads of the Multimetre between the points at the end of the arrows.

7. A parallel circuit is constructed by using the combination of the two resistors and finally by using all the three resistors. The values for the circuits are measured and recorded.

Part 3: Voltage in circuits

In part 2, the coded tolerance for the resistor is +5%. From the reading we obtain the percentage of errors is 1% and 2%. Thus it said that the data obtain is acceptable. In part 2, we conducted two experiment whereby in one experiment the resistor is arrange in series and in the other experiment the resistor is arrange in parallel. Base on the theory for series resistor we have:

Thus the equivalent resistance in the circuit is:

The rule for the total resistance when the resistor is arranged in parallel is as followed:

As a conclusion we can say that the data obtain in the experiment obey the rule.

        In part 3, we found out that the voltage gets distributed in a series circuit with equal resistance when the value of the resistor is the same. The larger the value of the resistor, the larger the value of the resulting voltage.

        In part 4, a voltage versus current was obtained. At a certain point in the graph, a straight line is obtain which directly prove Ohm’s Law which stated that the voltage, V is proportional to the current, I and the slope of the graph is the resistance.

Conclusion

        As a conclusion, we found out that the voltage, V is proportional to the current, I. The relationship for the variable V, I, R is V = IR