To study the dependence of current on the potential difference with graph
Aim
To study the dependence of current (I) on the potential difference (V) across a resistor and determine its resistance. Also plot a graph between V and I.
Materials Required
- Battery eliminator
- Ammeter
- Voltmeter
- Rheostat
- One way plug key
- Resistor
- Connecting wires
Theory
Ohm’s Law:
At constant temperature, the potential difference (V) across a conductor is directly proportional to the current (I) flowing through it.
Mathematically,
V ∝ I
or V = IR
or R = V/I
Where, R is constant of proportionality and is known as resistance.
Factors affecting resistance:
- Length of the conductor (R ∝ l)
- Cross-section area of the conductor (R ∝ 1/A)
- Nature of the material
Circuit Diagram

Procedure
- Setup the devices as shown in the circuit diagram.
- Note the least count of the ammeter and the voltmeter.
- Plug the key on the battery eliminator and adjust the rheostat by sliding its variable terminal till the ammeter and the voltmeter show a reading.
- Note the readings of voltmeter and ammeter. Take out the plug or switch off the battery eliminator for a moment.
- Repeat the steps 3 and 4 for the different values of current by varying the sliding terminal of rheostat.
- Calculate resistance using formula R = V/I.
- Plot a graph by taking I along y-axis and V along x-axis or vice-versa.
Observation Table
A. Least count and range of voltmeter and ammeter
Voltmeter | Ammeter | |
Range | 0 – 0.1 V | 0 – 0.5 A |
Least Count | 0.01 V | 0.01 A |
B. Readings of voltmeter and ammeter
S.No. | Potential difference (V) | Current (I) | Resistance R = V/I |
1. | 0.04 V | 0.02 A | R1 = 2 Ω |
2. | 0.06 V | 0.03 A | R2 = 2 Ω |
3. | 0.08 V | 0.04 A | R3 = 2 Ω |
*These observations may be different for different voltmeter, ammeter and resistors.
Calculation
Mean value of R = =
= 2 Ω
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 should be used as connecting wires and using sandpaper, their insulation should be removed.
- The connections should be tight.
- Voltmeter should be connected in parallel with the resistor.
- To avoid unnecessary heating in the circuit, the current should be passed for a short time.
Class 10 Electricity Notes Class 10 Electricity Previous Years Questions Class 10 Electricity Important Questions
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