AIM

To study the dependence of potential difference (V) across a resistor on the current (I) passing through it and determine Its resistance and also plotting a graph between V and I.

MATERIALS REQUIRED

Resistance wire, ammeter, voltmeter, battery eliminator, rheostat, One-way plug key, and connecting wires.

THEORY

Ohm’s Law states that “If the physical conditions such as temperature, pressure, etc., remain the same during the experiment, then the current (I) flowing is directly proportional to the potential difference (V) across the ends of the circuit.”

Mathematically,

V= IR or

Where,

1. The resistance(R) is the characteristic property of the conductor which resist the flow of electric current through it.

2. The potential difference (V) is the is the potential difference across the ends of a conductor.

3. The electric current (I) is the amount of charge flowing through a particular area in a unit time.

If we plot a graph between the current (I) and the applied potential difference(V) between its ends, for an ideal resistance it will be a straight line as shown:

Circuit Diagram

In the above diagram

Apparatus Arrangement :

The actual diagram of the Ohm’s Law apparatus is shown here:

PROCEDURE

1. By using the circuit diagram or apparatus arrangement, we set up the circuit for finding the dependence of voltage on the current flowing in the circuit.

2. Clean the end of connecting wires using with sandpaper to remove the insulation.

3. Determine the least count of the ammeter and voltmeter and note them under observation section.

4. Check for any zero error in the ammeter and voltmeter and if any record it in table ‘A.’

5. Switch on the battery eliminator, plug the key and adjust the resistance offered by the rheostat by sliding its variable terminal till the ammeter and the voltmeter show a reading.

6. Write the readings of ammeter and voltmeter in the observation table. Take out the key plug out of the circuit to make the circuit open.

7. Repeat the process done in step 4 and 5 for the different values of current by varying the sliding terminal of the rheostat and note down the reading for a respective value of voltage for current in the observation table.

8. Note all the observations in the observation table ‘B’ and then find the ratio of - for each set of observations. Find the mean value of R.

9. Plot a graph by taking I along the y-axis and V along the x-axis.

Observations:

OBSERVATION TABLE

1. Least count of ammeter:

The image of the ammeter is attached here:

The range of the ammeter =500 - 0 mA = 500 mA = 0.5 A

The number of divisions in between two consecutive values= 10

Therefore, the least count =

= 0.01 A

2. Zero error of ammeter:

The needle of the ammeter points towards zero of the main scale of the ammeter.

3. Least count of voltmeter:

The range of voltmeter = 2 - 0 V= 2 V.

The number of division in small scale between two division on the main scale

= 10

Therefore, the least count

4. Zero error of voltmeter = 0 V.

Table (B) for the reading of ammeter and voltmeter

S. No.	Voltmeter reading V (in volt)	Ammeter reading I (in ampere)
1.	0.20	0.1
2.	0.38	0.2
3.	0.62	0.3
4.	0.84	0.4
5.	1.08	0.5

CALCULATION

1. The ratio of V and I for each corrected set of observation is given in the table:

S. No.	Voltmeter reading V (in volt)	Ammeter reading I (in ampere)	(in ohm, Ω)
1.	0.20	0.1	2.00
2.	0.38	0.2	1.90
3.	0.62	0.3	2.07
4.	0.84	0.4	2.10
5.	1.08	0.5	2.16

The mean value of Resistance is calculated as:

=2.046 Ω ~ 2.05Ω

2. The graph between the potential difference ‘V’ along the x-axis and the current ‘F along the y-axis for I-Vgraph as shown or V’ on the y-axis and ‘I’ an x-axis is drawn:

3. Find the slope of the line.

(i) For I-V graph.

The slope of a line (Conductance)

Here, slope =

:. Resistance of nichrome (Or manganin) wire =1.97 Ω.

(ii) For the V-I graph,

The slope of Line Resistance of nichrome (or manganin)

RESULT

1. The linear nature of the I-V graph or V-I graph shows that potential difference across the end of the conductor is directly proportional to the current flowing through it,
i.e., V ∝ I. This proves the Ohm’s law graphically.

2. The resistance of the wire obtained from the graph is equal to the mean calculated value of R. It also verifies the Ohm’s law.

3. The resistance of the given wire = 2.05 Ω.

PRECAUTIONS

1. The ends of connecting wire should be rubbed using sandpaper.

2. All connections should be kept clean and tight.

3. The positive terminal of ammeter or voltmeter should be connected to the positive terminal of the battery or battery eliminator.

4. The ends of the resistance wire must be connected across the terminals of the voltmeter.

5. Remove the key out of the circuit when not in use to avoid the heating effect of the circuit.