Electric Field and Electric Potential

ELECTRIC FIELD AND ELECTRIC POTENTIAL

The flow of electricity in a circuit can be regarded very much similar to the flow of water in a pipe. The water pipe is analogous to an electrical conductor, while the amount of water flowing through a given point per second corresponds to electric current.Figure below shows how the pump (P) builds up arid maintains pressure by lifting water from a tank (B) to the reservoir (A) through the pipe (R). Note that along the pipe, different points are at different pressure. Water in the pipe flows from, say, a point C to D only when the pressure at C is greater than that at D. Thus, when the value (V) is open, water would start flowing into the reservoir.

In the same manner electrons will move along a wire only if there is a difference of electric pressure called potential difference along the conductor. This difference of potential is produced by the cell or a battery, which acts like a water pump in the circuit.

The chemical action within the cell generates the difference in potential between the electrodes, which sets the electrons in motion and produces the current. We define the electric potential difference between the two points, A and B, on a conductor carrying current, as the work done to move a unit charge from A to B. Potential difference (V) between the points A and B = work done (W)/charge (Q). The unit of potential is volt, named after a scientist Alessandra (1745-1827).

One volt is the potential difference when 1 joule of work is done to move a charge of 1 C.

ELECTRIC FIELD:

Electric field due to a given charge is defined as the space around the charge in which electrostatic force of attraction or repulsion due to charge can be experienced by any other charge. If a test charge experiences no force at a point, the electric field at that point must be zero.

Electric field intensity at any point is the strength of electric field at that point. It is defined as the force experienced by a unit positive charge placed at that point.

If is the force acting on a test charge +q0 at any point r, then electric field intensity at this point is given by

Electric field is a vector quantity and its S.I. unit is Newton per coulomb or N/C.

ELECTRIC POTENTIAL:

The work done in charging a body is stored in it as its electric potential energy. The electric potential energy per unit charge is called electric potential.

Electric Potential = Electric Potential Energy/Charge

Mathematically,

V =W/q

Since work is measured in joule and charge in coulomb, therefore electric potential is measured in joule per coulomb (J/C). This unit occurs so often in our study of electricity, so it has been named as volt, in honour of the scientist Alessandra Volta (the inventor of the voltaic cell).

1 Volt = 1 joule/ 1 coulomb

Potential is a scalar quantity, therefore it is added algebraically. For a positively charged body potential is positive and for a negatively charged body potential is negative.

ELECTRIC POTENTIAL DIFFERENCE:

Consider a charge Q placed at a point P. Let A and B be two other points (B being closer to A) as shown in figure.

P A B

If a charge q is brought from infinity to A, a work W_A will be done.

The potential at A will then be, VA = W_A/q

If charge q is brought from infinity to B, the work done will be WB.

The potential at B will then be, VB = W_B/q

The quantity VB-VA is called the potential difference between points A & B in the electric field of charge Q.

Mathematically we have,

Electric potential difference is also measured in volt.