Express Ohm's Law by a mathematical Formula & a graph
ohm 's law states that at constant temperature and under effect of no magnetic field , potential difference is directly proportional to the current flowing through the conductor .
Electrical circuit for Verification of Ohm 's Law:
To verify Ohm 's law, the following circuit is used.
The above diagram is of the circuit used in the lab for verification of ohm 's law.
In the circuit: B is the battery to supply the current to the circuit, Rh is rheostat to control the current in the circuit, K is key to connect or break the circuit, A is ammeter to measure the current in the circuit, V is the voltmeter to measure the potential difference across the resistance wire and R is a resistance wire to provide resistance.
Procedure for the Verification of Ohm 's Law:
1. Key K is closed and the Rheostat is adjusted so as to get minimum reading in the ammeter and voltmeter.
- The rheostat is then gradually moved so that the current in the circuit increases.
- Each time the rheostat is moved, the readings of the current (I) flowing in the circuit and potential difference across the resistance is measured by noting the readings of the ammeter and voltmeter.
- Thus, different sets of values are obtained in a table and the ratio of the current (I) and the potential difference (V) is calculated for each set of values.
- It is noted that the ratio of the current and potential difference is same or almost the same for each set of values in the table.
- Now a graph is plotted for V against I, in which the potential difference V is taken on the y axis and the current I is taken on the x axis.
- The graph obtained is a straight line and the slope of this line is the value of the ratio of V verses I.
Thus it is proved that the ratio of V verses I is a constant value (denoting resistance), that is, V/I = constant = R. Thus Ohm 's law is verified.