electric current and Its Effects - Class 7 Science - New St. Mery English School

Electricity plays an important role in our daily life. From lighting our homes to running fans, televisions, and mobile phones, everything depends on the flow of electricity. This flow of electric charge is called electric current. Without electric current, most of the modern machines we use today would not work.

In this chapter, Electric Current, students will learn what electric current is, how it flows through a circuit, and how it helps electrical devices to function. We will also study electric cells, batteries, switches, and conductors, which are necessary for the flow of electric current. Understanding this topic will help students know how electricity is produced, controlled, and used safely in our everyday life.

This lesson builds a strong foundation for learning more about electricity in higher classes and helps students become more aware of energy and its uses.

electric current and Its Effects - Class 7 Science - New St. Mery English School

Electric current is the flow of electric charges (usually electrons) through a conductor like a wire.

👉 Electric current is the movement of electricity from one place to another.

It is represented by 'I'

Example:

When you switch on a bulb, electric current flows through the wire to the bulb and makes it glow 💡.

Unit:

Electric current is measured in ampere (A).

Electric Current = Electric Charge / time

I = Q / t

Where:

I = Electric current (in ampere, A)

Q = Electric charge (in coulomb, C)

t = Time (in seconds, s)

The SI unit of electric current is Ampere because electric current cannot be measured directly, but its magnetic effect can be measured very accurately.

When electric current flows through a wire, it produces a magnetic field around it. Scientists found that this magnetic effect can be measured very precisely. So, they decided to define electric current using this effect.

Scientific idea:

One ampere is the amount of current which, when flowing through two parallel wires, produces a fixed magnetic force between them.

In simple words:

👉 Ampere is used as the SI unit because it allows electric current to be measured accurately and reliably.

Who was André-Marie Ampère?

André-Marie Ampère (1775–1836) was a French physicist and mathematician.

He is known as the “Father of Electrodynamics.”

Why is the unit named Ampere?

He discovered the relationship between electricity and magnetism.

His work showed that electric current produces magnetic effects, which is the basis for motors, generators, and many electrical devices.

To honor his contribution: 👉 The SI unit of electric current was named “Ampere (A)” after him.

Numerical 

Q1. If 10 coulomb of charge flows in 5 seconds, find the electric current.

Q2. A charge of 30 C flows through a wire in 10 s. Find the current.

Electric charge 

Electric Charge is a property of matter that causes it to experience electrical force.

In simple words:

👉 Electric charge is the reason why objects attract or repel each other electrically.

It is represented by 'Q'

Types of electric charge

There are two types:

Positive charge

Negative charge

Example:

When you rub a balloon on your hair, it gets electric charge and can stick to a wall 🎈. This happens because of electric charge.

The SI unit of electric charge is Coulomb.

Symbol - C

👉 1 coulomb (C) is the amount of charge that flows when 1 ampere of current flows for 1 second.

Electric Charge = Electric Current × Time 

Who was Charles-Augustin de Coulomb?

Charles-Augustin de Coulomb (1736–1806) was a French physicist.

He studied the forces between electric charges and magnetic poles.

Why is the unit named Coulomb?

He discovered a law called Coulomb’s Law, which explains: 👉 How electric charges attract or repel each other.

To honor his work, the SI unit of electric charge was named “Coulomb (C)” after him.

Numerical 

Q1. How much charge flows if a current of 5 A flows for 4 seconds?

Q2. A current of 2 A flows for 15 seconds. Find the charge.

How many types of substances on the basis of electric current 

Ans:- There are two types of substances on the basis of electric current.

1- Conductors 

2- Insulators 

What are Conductors?

Ans:- Substances which allow electric current to flow through them are called conductors.

Ex:- Metals like aluminium, iron, copper, etc, alkali solutions, acid solutions, etc. are good conductors of electricity

What are Insulators?

Substances which do not allow electric current to flow through them are called insulators.

Ex:- Wood, plastic, paper, rubber, air, etc.

Electric Circuit 

What is electric Circuit?

Ans:- The path along which electric current flows is called electric circuit. An electric circuit consists of a number of components like cell or battery, connecting wires, switch, bulb etc. These components are called the elements of an electric circuit. The elements of a circuit are connected between the two terminal of a cell that is( +ve and -ve ). The current starts from the positive terminal of a cell, passes through the various conducting elements connected to it and ends at the negative terminal of the cell

How many types of electric Circuit?

There are two types of electric Circuit 

1- Closed electric Circuit 

2- Open electric Circuit 

What is Closed electric Circuit?

Ans- The circuit in which the various components are connected between the cells without any break is called a closed electric circuit.

Electric current flows through a closed circuit.

What is Open electric Circuit?

Ans- The circuit in which the various components connected between the cells have a break at some point is called an open electric circuit.

No current flows through an open circuit.

Elements of Circuit 

Cell  - : Cell is the source of electric current. It has two terminals, one positive and the other negative. The most commonly used cell in the laboratory is the dry cell.

Battery - the combination of two or more cells to produce electric current is called battery. In a battery the individual cells are connected in series or parallel.

How many types of battery? 

There are two types of battery. 

1- battery with cells in series 

2- battery with cells in parallel 

Battery with cells in series

In this kind of battery, the individual cells are connected in such a way that positive terminal of one cell is connected to the negative terminal of the other cell.

Battery with cells in parallel 

In this kind of battery, the individual cells are connected in such a way that their positive terminals are connected to each other and the negative terminals connected to each other with one free positive and one free negative terminal.

Switch 

Switch is a simple device used to turn an electric circuit ON or OFF.

Switch is another important element of the

circuit. It helps us to close or open the circuit. When the switch is in 'ON' position, the current flows through the circuit. The circuit is now said to be closed. On the other hand, when the switch is in 'OFF' position, no current flows through the circuit. The circuit is now said to be open.

A switch does not have terminals and can be connected anywhere in the circuit.

Bulb

An electric bulb is a device that produces light when electric current passes through it.

Inside the bulb there is a very thin wire called a filament. When electricity flows through the filament, it becomes very hot and glows, giving us light.

The bulb has a thin wire, called the filament that glows when current passes through it. If the filament is broken, the bulb will not glow. It is then said to be fused. A fan uses electric current to rotate to blow air.

Connecting wire

It is used to connect various components in an electric circuit. It is made of copper or aluminium coated with insulating material like plastic.

Voltmeter 

Ammeter 

Why are symbols for some electric components used instead of components?

Symbols for electric components are used in a circuit diagram instead of drawing the real components because:

1. They make diagrams simple and clear

Real components are big and complicated to draw. Symbols are small and easy, so the diagram looks neat.

2. They save time and space

Using symbols is much faster than drawing actual bulbs, cells, wires, etc.

3. They are understood all over the world

Electric symbols are standard. Scientists, engineers, teachers, and students everywhere understand the same symbols.

4. They help us understand the circuit easily

Symbols show how components are connected, so we can quickly follow the flow of electric current.

5. They avoid confusion

Real drawings may look different, but symbols are fixed, so there is no misunderstanding.

Some commonly used diagram of components are shown below 

Volt

Volt is the force that pushes electric charges. Volt is the unit that tells us how strong the push of electricity is. 

Volt (V) is the unit of electric potential difference. 

One volt is the potential difference when 1 joule of energy is used to move 1 coulomb of charge.

1 volt = 1 Joule / 1 Coulomb 

📌 Example

A 1.5 V battery gives small push (used in toys)

A 12 V battery gives stronger push (used in vehicles)

220 V is used in homes