Chapter 14 Electric Current and its Effects Class 7 Notes


Electric Current and its Effects Class 7 Notes

Here we are providing you with the Electric Current and its Effects Class 7 Notes. These short and concise Electric Current and its Effects Class 7 Notes will surely help you in your exams and also give you an understanding of the chapter Electric Current and its Effects.

Electric Current

Define Electric Current.

Electric Current is defined as the rate of flow of electric charges in a closed circuit.

What is the Unit of Electric Current?

The SI Unit of Electric Current is Ampere. It is denoted by the English letter A.

Note: Conventionally, the direction of the electric current is taken from the positive terminal to the negative terminal of a cell.

Electric Circuit

What is an Electric Circuit?

An electric circuit is a closed path in which electrons move to produce electric currents.

The electric circuit diagram consists of a key that acts as a switch for the circuit. The key can be placed anywhere in the circuit.

Define Open Circuit and Closed Circuit.

Open Circuit – When the key is switched off or opened the circuit is said to be an open circuit as it is incomplete.

Closed Circuit – When the key is switched on or closed the circuit is said to be a closed circuit as it is complete.

  • Electric current can flow only through a closed circuit.

Electric Circuit Components

What are the Electric Circuit Components? Name them.

Electric Circuit consists of many components. The main Electric Circuit Components are-

  • Cell or battery
  • Switch
  • Circuit Appliance (Bulb, etc.)
  • Wire

Cell

What is a Cell?

  • A cell is a source of current.
  • It has a positive and a negative terminal.
  • It converts stored chemical energy into electrical potential energy.

Battery

What is a Battery?

When two or more cells are connected such that the positive terminal of one cell touches the negative terminal of the other, it forms a battery.

For the electric current to flow the cells must be connected properly, i.e., either connected in series or in parallel.

Switch

A switch is an electrical component that is used to close or open a circuit.

When the switch is off, the circuit is open and no current flows through it.

When the switch is on the circuit is closed allowing current to flow.

Electrical Appliance

It is a device that uses the current flowing through it to function.

Electric bulbs, Electric Iron, Fans, and Electric Motors are some commonly used electrical appliances in our daily life.

Wires

Wires help in connecting the elements of the electric circuit.

It is made up of material that is a good conductor of electricity. Generally, Ex- Copper (Cu), Aluminium (Al), and Silver (Ag).

Generally, commercial wires are made up of Copper and Aluminium as they are cheap.

Circuit Diagram

A schematic diagram that represents an electric circuit using the standard symbols of the components used in the circuit is called a circuit diagram.

Heating Effect of Electric Current

What is the Heating Effect of Electric Current? 

When an electric current passes through a wire the wire gets heated up. This is known as the heating effect of electric current.

The heat that is produced in the wire depends upon the following factors –

  • the material of the wire
  • the length of the wire
  • the thickness of the wire

Appliances Working on Heating Effect of Electric Current

Here is the list of some appliances Working on the Heating Effect of Electric Current-

  • electric heater
  • electric iron
  • electric stove
  • geysers
  • electric coffee maker
  • toaster

Electric Fuse

What is an Electric Fuse?

It is a safety device to protect the electric circuit and devices in the circuit.

Electric fuse works on the principle of the heating effect of electric current.

It is made up of a material having a low melting point.

The metal or alloy of tin and lead is used which has a low melting point.

On the passing of an excess amount of current (more than the designated amount of current), the fuse breaks due to the heating effect of current.

This breaks the circuit and the circuit becomes an open circuit. Now no current can flow through it and the devices in the circuit are safe.

The quantity of heat produced in a conductor by a current depends on the amount of current flowing through the conductor.

Magnetic Effect of Electric Current

What do you understand by the Magnetic Effect of Electric Current?

When an electric current is passed through a wire it behaves like a magnet. This is called the magnetic effect of the electric current.

It was discovered by Hans Christian Oersted.

He placed a compass near an electric current-carrying wire. He discovered that the needle of the compass deflects. This indicates that a magnetic field is created near the wire when it carries current.

Solenoid

What is a Solenoid?

It is a cylindrical coil of a wire. It behaves like a magnet when an electric current is passed through it.

Electromagnet

What is an Electromagnet?

An Electromagnet is a device that acts as a magnet when a current flows through its coil.

It consists of a magnetic material such as a soft iron piece and a coil of insulated copper wire tightly wound around it.

The material on which the insulated wire is wound is called it’s core.

It is a temporary magnet that loses its magnetic property when the current through the circuit is withdrawn.

Strength of the Magnetic Field-

What are the factors that define the strength of a Magnetic Field?

  • Amount of current passing
  • No. Of turns of the wire

Applications of Electromagnets

Electric Magnets are used for the following perposes-

  • Electromagnets are used in domestic appliances such as electric bells
  • They are used in toys
  • Electromagnets are used in Electronic devices such as television, radio, and tape recorder
  • Electromagnets are used to separate magnetic materials from piles of junk
  • Electromagnets are also used in trains
  • Electromagnets are used in cranes to lift heavy objects like cars, buses, etc.
  • Electromagnets are used by doctors to remove any magnetic materials that we have fallen in the eye.

Electric Bell

What is an Electric Bell?

Electric Bell is a device that produces sound when electricity is passed through it. It is commonly used in houses, schools, offices, factories, etc. for ringing purposes.

Let us look at the components of an Electric Bulb and the Working of an Electric Bulb.

Components of Electric Bell

What are the components of an Electric Bulb?

The main components of an Electric Bulb are-

  1. Push Switch
  2. Battery
  3. Electromagnet
  4. Gong
  5. Striker

Working of Electric Bell

Write the Working of an Electric Bulb or How does an Electric Bulb?

On pushing the switch the circuit closes and the current starts flowing from the positive terminal to the negative terminal. When current flows through the coil it becomes an electromagnet. This electromagnet attracts the soft iron towards it and the striker strikes the gong (bell). But once the striker hits the bell the circuit opens or breaks due to the shifting of the soft iron from its original position. This break demagnetizes the coil, and the soft iron shifts to its original position and again completes the circuit. This process will continue till the switch is switched off. This is how an electric bell works.

ISI Mark

What is an ISI mark?

ISI stands for Indian Standards Institute which standardizes all electrical appliances.

Hence if any appliance does not have an ISI mark over it, it means that this appliance does not conform to the standard guidelines of ISI and hence it is not safe to use.

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