Electric Potential and Potential Difference
- Electric charges do not flow in a metallic conductor (e.g., copper wire) by themselves. Here, gravity has no role.
- Electrons move only if there is a difference of electric pressure in the conductor. It is called potential difference.
- Potential difference can be produced by a battery. 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, the potential difference sets the charges in motion and produces an electric current. To maintain this current, the cell has to expend chemical energy stored in it.
- The potential difference between two points in an electric circuit is 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 or W = VQ
- The SI unit of electric potential difference is volt (V), named after Alessandro Volta (Italy, 1745–1827).
- One volt is the potential difference between two points in a current-carrying conductor when 1 joule of work is done to move 1 coulomb charge from one point to another.
- Voltmeter: An instrument to measure potential difference. It is always connected in parallel across points between which the potential difference is to be measured.
- Problem: How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V?
Solution:
Amount of charge Q = 2 C.
Potential difference V = 12 V.
Amount of work W = VQ.
= 12 V × 2 C = 24 J.
Circuit Diagram
Conventional symbols of some commonly used components in circuit diagrams:
