CBSE Class 8 Science Notes Chapter 4, Download PDF

Electric Current

• Electric current is the flow of electric charges (electrons) through a conductor.

• Electric current is measured in Ampere (A) using an Ammeter (always connected in series).

• Potential difference is measured in Volts (V) using a Voltmeter (connected in parallel).

Formula:

• Where I = current, V = voltage, R = resistance

• This is Ohm’s Law.

Electric Circuit

• Electric circuit is a complete path for current to flow.

• Circuit components: cell, battery, wires, switch, bulb, resistor.

• Closed circuit → current flows

• Open circuit → current does not flow

Electrical Circuit Diagram Components:

• Plug key

• Cell (+, −)

• Electric bulb

Magnetic Effect of Electric Current

• Discovered by Hans Christian Oersted.

• When electric current passes through a conductor, a magnetic field is produced around it.

Important Points

• Magnetic field is stronger near the wire and decreases with distance.

• The field around a straight wire forms concentric circles.

• Right-hand Thumb Rule
  → Thumb = direction of current

Electromagnet

A temporary magnet created when current flows through a coil wire (solenoid) wrapped around a soft iron core.

Factors Affecting Strength of an Electromagnet

1. Increasing number of turns of coil

2. Increasing current

3. Using soft iron core

4. Thick, uniform coil

Uses of Electromagnets

• Electric bell

• MRI machines

• Cranes (lifting scrap iron)

• Motors

• Relays

Electric Bell (Working)

• Contains an electromagnet.

When current flows:

1. Electromagnet attracts the iron armature.

2. Hammer hits the bell.

3. Contact breaks → current opens → magnet loses magnetism.

4. Spring pulls armature back → contact is restored.

5. Cycle repeats rapidly creating ringing sound.

Heating Effect of Electric Current

• When electric current flows through a conductor, it produces heat.

Where

• H = heat produced

• I = current

• R = resistance

• t = time

More Current = More Heat

• More resistance = more heat

Applications of Heating Effect

1. Electric iron, toaster, geyser, heater

• Work on heating effect

2. Electric bulb (Filament)

• Has a tungsten filament

• High melting point → glows without melting

3. Fuse

• Is a safety device

• Made of low melting point metal

• Prevents overheating by breaking the circuit when excessive current flows

CFL, LED (Energy Efficient Devices)

• CFL uses less electricity than filament bulbs

• LED uses even less energy, produces less heat

• Long-lasting and eco-friendly

Difference Between Magnetic & Heating Effect

Important Formulas

Electricity: Magnetic and Heating Effects Notes PDF by PW

The Electricity: Magnetic and Heating Effects PDF by Physics Wallah provides a concise summary of all important concepts covered in Chapter 4. It includes definitions, diagrams, working principles, applications, and key exam-oriented points that help students revise the chapter efficiently.

Students can use the PDF for quick revision before tests and exams, making it easier to understand concepts such as electromagnets, electric bells, fuse wires, MCBs, and the heating effect of electric current without referring to lengthy textbook explanations.

Electricity: Magnetic and Heating Effects PDF

How PW Class 8 Science Notes Help in Exam Preparation?

PW Class 8 Science Notes are designed to simplify complex concepts and help students revise the syllabus efficiently. These notes present important definitions, diagrams, examples, and key points in a structured format, making learning more effective.

1. Simplified Explanations

Concepts such as electromagnets, electric bells, fuse wires, and MCBs are explained in easy-to-understand language, helping students grasp the fundamentals quickly.

2. Quick Revision Resource

The notes combine the entire chapter into concise points, allowing students to revise important topics in less time before exams.

3. Focus on Important Concepts

Key topics like the magnetic effect of current, heating effect of current, and electrical safety devices are highlighted to help students focus on exam-relevant content.

4. Better Concept Retention

Organized explanations and examples make it easier to remember important concepts and their real-life applications.

5. Useful for School Exams and Assessments

The notes cover all major topics from the CBSE syllabus, making them ideal for periodic tests, unit tests, and final examinations.