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

1. Setup the devices as shown in the circuit diagram.
2. Note the least count of the ammeter and the voltmeter.
3. 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.
4. Note the readings of voltmeter and ammeter. Take out the plug or switch off the battery eliminator for a moment.
5. Repeat the steps 3 and 4 for the different values of current by varying the sliding terminal of rheostat.
6. Calculate resistance using formula R = V/I.
7. 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

Calculation

Mean value of R = = = 2 Ω

Graph

Conclusions

1. For all the three readings, the R-value is the same and constant.
2. The ratio of potential difference V and current I is the resistance of a resistor.
3. With the help of the graph between V and I, Ohm’s law is verified as the plot is a straight line.

Precautions

1. Thick copper wires should be used as connecting wires and using sandpaper, their insulation should be removed.
2. The connections should be tight.
3. Voltmeter should be connected in parallel with the resistor.
4. To avoid unnecessary heating in the circuit, the current should be passed for a short time.

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