General Science Notes Chapter 8 Class 7 Maharashtra Board

Notes For All Chapters – General Science Class 7

Static Electricity

1. Introduction

Electricity is an important part of our daily lives.

There are two types of electricity:

1. Static Electricity – Electricity that stays on the surface of an object.
2. Current Electricity – Electricity that flows through wires to power devices.

Static electricity is generated when two objects are rubbed together.

2. Discovery of Static Electricity

• Thales, a Greek scientist, discovered that when amber is rubbed with fur, it attracts small objects.
• William Gilbert studied this and called it electric charge.
• Benjamin Franklin later named the charges positive (+) and negative (-).

3. Electric Charge

Every object has tiny particles called atoms.

Atoms contain:

• Protons (+) – Positive charge
• Electrons (-) – Negative charge
• Neutrons – No charge

How Electric Charge is Created

• When two objects are rubbed together, some electrons transfer from one object to another.
• The object that loses electrons becomes positively charged (+).
• The object that gains electrons becomes negatively charged (-).

Properties of Electric Charge

Like charges repel (push away).

• Example: Two positive charges repel each other.

Opposite charges attract (pull together).

• Example: A positive and a negative charge attract each other.

4. Types of Electricity

5. Uses and Effects of Static Electricity

A. Examples of Static Electricity in Daily Life

• Rubbing a balloon on hair → Hair sticks to the balloon.
• Clothes sticking together after drying → Static charge causes attraction.
• Lightning in the sky → A large discharge of static electricity.

B. How Does a Charged Object Attract an Uncharged Object?

• A charged object induces an opposite charge in the uncharged object.
• Example: A charged balloon sticks to a wall because it attracts opposite charges from the wall.

6. Lightning – A Natural Static Electricity

What is Lightning?

• Lightning is a large spark of static electricity that occurs between clouds and the ground.
• It happens when negative charges from clouds move towards the positive charges on the ground.

How Lightning Occurs?

1. Clouds move and rub against each other, creating a charge.
2. The bottom of the cloud becomes negatively charged (-).
3. The ground becomes positively charged (+).
4. The negative charges suddenly rush towards the ground, causing a bright flash of lightning.

7. Lightning Protection

A. Lightning Conductor

• A lightning conductor is a metal rod placed on buildings to protect them from lightning.
• It directs the charge safely into the ground and prevents damage.

B. Safety Measures During Lightning

DO’s (Safe Places)

✔ Stay indoors or inside a car.

✔ Stay away from windows, doors, and electrical appliances.

✔ If outside, crouch low on the ground with hands on knees.

DON’Ts (Unsafe Places)

❌ Do not stand under trees or open fields.

❌ Do not use metal objects like umbrellas or bicycles.

❌ Do not take a shower or use electrical appliances during a thunderstorm.

8. Electroscope – A Device to Detect Electric Charge

• An electroscope is a device that detects whether an object is charged or not.
• It has a metal rod and thin metal leaves inside a jar.
• If the object has charge, the metal leaves move apart due to repulsion.

9. Key Differences Between Static and Current Electricity