Ohm’s Law Our aim is to determine the resistance per
centimeter of a given wire by plotting a graph of potential difference versus current, and
hence to determine its resistivity. To do the experiment, we require the following:
screw gauge, battery, one way key, rheostat, voltmeter, ammeter, measuring scale and resistance
wire. Connect the positive terminal of battery to
the positive terminal of ammeter using a connecting wire.
Connect the negative terminal of ammeter to the positive terminal of voltmeter using a
connecting wire. The negative terminal of voltmeter is connected
to the upper terminal of rheostat using a piece of wire.
Connect the lower terminal of the rheostat to one end of the one way key (key should
be removed) using a connecting wire. The other free end of one way key is connected
to the negative terminal of battery. Now take a resistance wire, stretch it and
measure its length using a meter scale and cut the wire at the given point.
Connect it parallel to the terminals of voltmeter (i.e., Positive to Negative).
The connection is completed. Now, insert the key and slide the rheostat
contact to check the working of ammeter and voltmeter.
Adjust the sliding contact of the rheostat and note down the value of potential difference
V from voltmeter and current I from ammeter. Record the reading of voltmeter and ammeter.
Shift the rheostat contact slowly and record the reading of voltmeter and ammeter and calculate
the value of R in each case. Shift the rheostat contact slowly.
Similarly, take at least five sets of independent observations.
Record the readings and plot a graph with the values.
Calculate the resistance per centimeter of the wire.
Calculate the least count and zero correction of the screw gauge.
Remove the resistance wire from the terminals of voltmeter.
The resistance wire is gently gripped between the stud and the screw of the screw gauge.
Note the pitch scale reading and head scale reading.
Calculate the diameter of the wire and hence the radius of the wire.
Calculate the resistivity (specific resistance) of the material of the wire.
Resistance per centimeter of the given wire is 0.066 ohms per centimeter and resistivity
of the material of the given wire is 1.01 x 10-6 ohms meter