Electricity PDF - Electric Potential and Potential Difference

11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE What makes the electric charge to flow? Let us consider the analogy of flow of water. Charges do not flow in a copper wire by themselves, just as water in a perfectly horizontal tube does not flow. If one end of the tube is connected to a tank of wate...

11.2 ELECTRIC POTENTIAL AND POTENTIAL DIFFERENCE What makes the electric charge to flow? Let us consider the analogy of flow of water. Charges do not flow in a copper wire by themselves, just as water in a perfectly horizontal tube does not flow. If one end of the tube is connected to a tank of water kept at a higher level, such that there is a pressure difference between the two ends of the tube, water flows out of the other end of the tube. For flow of charges in a conducting metallic wire, the gravity, of course, has no role to play; the electrons move only if there is a difference of electric pressure – called the potential difference – along the conductor. This difference of potential may be produced by a battery, consisting of one or more electric cells. The chemical action within a cell generates the potential difference across the terminals of the cell, even when no current is drawn from it. When the cell is connected to a conducting circuit element, the potential difference sets the charges in motion in the conductor and produces an electric current. In order to maintain the current in a given electric circuit, the cell has to expend its chemical energy stored in it. We define the electric potential difference between two points in an electric circuit carrying some current as the work done to move a unit charge from one point to the other – Potential difference (V) between two points = Work done (W )/Charge (Q) V = W/Q (11.2) The SI unit of electric potential difference is volt (V), named after Alessandro Volta (1745 –1827), an Italian physicist. One volt is the potential difference between two points in a current carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to the other. 1 joule Therefore, 1 volt = 1 coulomb (11.3) 1 V = 1 J C–1 The potential difference is measured by means of an instrument called the voltmeter. The voltmeter is always connected in parallel across the points between which the potential difference is to be measured. Example 11.2 How much work is done in moving a charge of 2 C across two points having a potential difference 12 V? Solution The amount of charge Q, that flows between two points at potential difference V (= 12 V) is 2 C. Thus, the amount of work W, done in moving the charge [from Eq. (11.2)] is Electricity 173 2024-25