Charge, Current and Potential Difference

Current

The rate of flow of charge, represented by I = △Q/△t where I is current in amperes, △Q is charge in coulombs, and △t is time in seconds.

Coulomb

The unit of charge, where 1 coulomb (C) is the charge passing in 1 second at a current of 1 ampere.

Potential Difference

The work done per unit charge, defined as V = W/Q where V is potential difference in volts, W is work done in joules, and Q is charge in coulombs.

Charge Carriers

Particles responsible for current flow, such as free electrons in metals, ions in liquids and gases, with different materials having varying number densities (n).

Mean Drift Velocity

The average velocity of charge carriers, much less than their actual speed, given by I = nqvA where I is current, n is number density, q is charge, v is drift velocity, and A is cross-sectional area.

Metals vs

Metals have many charge carriers (large n) with low drift velocity, semiconductors have fewer carriers requiring higher drift velocity, and insulators have minimal carriers (n ≈ 0) resulting in no current flow.

Q1 How are current and charge related in words and symbols?

Current (I) is the rate of flow of charge (Q) and is measured in amperes (A). It can be represented by the equation I = Q/t, where I is current, Q is charge, and t is time.

Q2 What is the definition of potential difference?

Potential difference, also known as voltage, is the energy transferred per unit charge when moving a positive test charge between two points in an electric field. It is measured in volts (V).

Q3 What happens to the current in a wire if the mean drift velocity of the electrons is halved?

If the mean drift velocity of electrons in a wire is halved, the current in the wire remains the same. This is because current is determined by the number of charge carriers passing a point per unit time, not the speed of the charge carriers.

Q4 How do metals, semiconductors, and insulators differ in terms of n?

Metals have a high density of free electrons (n), semiconductors have a moderate density of free electrons, and insulators have a very low density of free electrons. The parameter n represents the number of charge carriers per unit volume in a material.