Chapter 11 · Question 1

Define electric current and an electric circuit. How many electrons make up one coulomb of charge?

Answer Revealed

Direct Answer:

Electric current is the rate of flow of electric charge through a conductor. An electric circuit is a continuous and closed conducting path along which an electric current flows. Nearly

6 \times 10^{18}

electrons constitute one coulomb of charge.

Simple Explanation

Think of electric current as the amount of charge flowing per second — like measuring how much water passes through a pipe per second. A circuit is just the complete loop the current needs to flow. One coulomb of charge is made up of about

6 \times 10^{18}

electrons — that is an enormous number of tiny charge carriers.

Exam-Ready Structure

Electric current and electric circuit are fundamental concepts in electricity: 1. Electric current (I) is defined as the rate of flow of electric charge (Q) through any cross-section of a conductor. Mathematically,

I = Q / t

, where Q is the net charge flowing in time t. 2. The SI unit of electric current is the ampere (A). One ampere is the current when one coulomb of charge flows through a conductor in one second. Smaller units are milliampere (

1\ \text{mA} = 10^{-3}\ \text{A}

) and microampere (

1\ \mu\text{A} = 10^{-6}\ \text{A}

). 3. An electric circuit is a continuous and closed path consisting of conducting wires and other electrical components (like a cell, bulb, switch, etc.) through which an electric current flows. 4. Conventionally, the direction of electric current is taken as opposite to the direction of flow of electrons. Electrons flow from the negative terminal to the positive terminal, but conventional current is taken to flow from the positive terminal to the negative terminal of the cell. 5. One coulomb of charge is equivalent to the charge carried by nearly

6 \times 10^{18}

electrons. This is because the charge on one electron is approximately

1.6 \times 10^{-19}\ \text{C}

, so

1\ \text{C} / (1.6 \times 10^{-19}\ \text{C})

approximately equals

6 \times 10^{18}

electrons.

Key Points

Electric current ( $I$ ) is the rate of flow of charge: $I = Q / t$
SI unit of current is ampere (A); $1\ \text{A} = 1\ \text{C} / 1\ \text{s}$
An electric circuit is a continuous, closed conducting path
Conventional current direction is opposite to electron flow (positive to negative terminal)
One coulomb of charge contains nearly $6 \times 10^{18}$ electrons

Common Mistakes

Saying current flows from negative to positive (that is electron flow; conventional current flows positive to negative)
Confusing the direction of electron flow with the direction of conventional current

Define electric current and an electric circuit. How many electrons make up one coulomb of charge?