To study the dependence of current on the potential difference with graph
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.
- Battery eliminator
- One way plug key
- Connecting wires
At constant temperature, the potential difference (V) across a conductor is directly proportional to the current (I) flowing through it.
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
- 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.
A. Least count and range of voltmeter and ammeter
|Range||0 – 0.1 V||0 – 0.5 A|
|Least Count||0.01 V||0.01 A|
B. Readings of voltmeter and ammeter
|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|
Mean value of R = = = 2 Ω
- 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.
- 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.