The dependence of potential difference (V) across a resistor on the current (I)?
Experiment No. 04
Aim
To study the dependence of potential difference (V) across a resistor on the current (I) passing through it and determine its resistance. Also, plot a graph between V and I
Theory
What is Ohm’s law?
In an electric circuit, the potential difference V across the metallic wire is directly proportional to the current flowing through the circuit with a constant temperature. This is known as Ohm’s law.
V∝I. ∴ V=IR.
What are the factors affecting resistance?
Following are the factors affecting resistance:
- The nature of the resistor.
- With an increase in length, the resistance also increases. So length also affects the resistance.
- With an increase in the cross-sectional area, the resistance decreases. So cross-sectional area of the wire affects the resistance.
Materials Required
Following is the list of materials required for this experiment:
- A battery
- An insulated copper wire
- A key
- An ammeter
- A voltmeter
- A rheostat
- A resistor
- A piece of sandpaper
Circuit Diagram

Procedure
- Arrange the devices as shown in the circuit diagram.
- Connect the devices with the connecting wires keeping the key open.
- The positive terminal of the battery should be connected to the positive terminal of the ammeter.
- Before connecting the voltmeter in the circuit, check for +ve and -ve terminals.
- Check for ammeter and voltmeter reading once the circuit is connected and also adjust the slider of rheostat after inserting the key.
- For current I and voltmeter V, record three different readings using a slider.
- Record the observations in the observation table.
- Using the formula R=V/I, calculate the resistance.
- To plot the graph between V and I, take V on the x-axis and I on the y-axis.
- For pure metals, resistance increases with an increase in temperature.
Observation Table
i) Least count of ammeter and voltmeter
S.No. | Ammeter (A) | Voltmeter (V) | |
1 | Range | 0-0.5 A | 0-0.1 V |
2 | Least count | 0.01 A | 0.01 V |
3 | Zero error (e) | 0 | 0 |
4 | Zero correction | 0 | 0 |
ii) For the reading of ammeter and voltmeter
S. No | Current in Ampere (I) (ammeter reading) | Potential difference in volts (V) (voltmeter reading) | Resistance in ohms R = V/I (Ω) | ||
Observed | Corrected | Observed | |||
1 | 0 | 0.02 | 0 | 0.04 | R1= 2Ω |
2 | 0 | 0.03 | 0 | 0.06 | R2= 2Ω |
3 | 0 | 0.04 | 0 | 0.08 | R3= 2Ω |
Graph

Conclusions
- For all the three readings, the R-value is the same and constant.
- The ratio of potential difference V and current I is the resistance of a resistor.
- With the help of the graph between V and I, Ohm’s law is verified as the plot is a straight line.
Precautions
- Thick copper wires are used as connecting wires and using sandpaper, their insulation is removed.
- To avoid external resistance, the connections should be tight.
- The connections should be as per the circuit diagram and should be approved by the teacher before conducting the experiment.
- The current should enter from the positive terminal and exit from the negative terminal of the ammeter and should be connected in series with the resistor.
- Resistor and voltmeter should be connected in parallel.
- The least count of ammeter and voltmeter should be recorded properly.
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The dependence of potential difference (V) across a resistor on the current (I)?
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