Solved Problem -2

Solved Problem - The work done in moving a charge of C across two points in a circuit is J. What is the potential difference between the points? Electricity Solution: Charge, Q = C Work Done, W = J Potential Difference V = = . Therefore, V = volt . OHM’S LAW A German physicist, Georg Simon Ohm established the relation between the potential difference and current, which is known as Ohm’s Law. This relationship can be understood from the following activity. Figure . Electric circuit to understand Ohm’s law According to Ohm’s law, at a constant temperature, the steady current ‘I’ flowing through a conductor is directly proportional to the potential difference ‘V’ between the two ends of the conductor. I V. Hence, = constant. The value of this proportionality constant is found to be Therefore, I = V V = I R ( . ) Here, R is a constant for a given material (say Nichrome) at a given temperature and is known as the resistance of the material. Since, the potential difference V is proportional to the current I, the graph between V and I is a straight line for a conductor, as shown in the Figure . . Figure . Relation between potential difference and current . RESISTANCE OF A MATERIAL In Figure . , a Nichrome wire was connected between X and Y. If you replace the Nichrome wire with a copper wire and conduct the same experiment, you will notice a different current for the same value of the potential difference across the wire. If you again replace the copper wire with an aluminium wire, you will get another value for the current passing through it. From equation ( . ), you have learnt that V/I must be equal to the resistance of the conductor used. The variations in the current for the same values of potential difference indicate that the resistance of different materials is different. Now, the primary question is, “what is resistance?” Resistance of a material is its property to oppose the flow of charges and