Electrostatics – Stage 0 (Foundation)

Chapter 1: Electric Charges & Fields – Page 3

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1. What Determines Electrical Behaviour of Matter?

The electrical behavior of a material depends on the mobility of electrons inside it.

• If electrons move freely → good conductor
• If electrons are tightly bound → insulator

JEE Foundation: Electricity is governed by electron freedom, not by number of protons.

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2. Conductors

Conductors are materials in which electrons can move freely throughout the substance.

Examples:

• Metals (Copper, Aluminium, Silver)
• Human body
• Earth

Key Properties:

• Large number of free electrons
• Low resistivity
• Charge resides only on the surface (in electrostatics)

Very Important (JEE): In electrostatic equilibrium, electric field inside a conductor is zero.

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3. Insulators

Insulators are materials in which electrons are tightly bound to atoms and cannot move freely.

Examples:

• Glass
• Plastic
• Rubber
• Mica

Key Properties:

• No free charge flow
• High resistivity
• Can be polarized

JEE Trap: Insulators can still respond to electric fields via polarization.

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4. Semiconductors (Brief JEE Awareness)

Semiconductors lie between conductors and insulators.

• Limited free electrons
• Conductivity increases with temperature

Examples: Silicon, Germanium

Note: Detailed study comes in XII (Current Electricity & Electronics).

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5. Polarization of Dielectrics

When an electric field is applied to an insulator, charges inside the atoms shift slightly.

• Positive charges shift in field direction
• Negative charges shift opposite to field

This separation of charges is called polarization.

JEE Concept: Polarization reduces the effective electric field inside the dielectric.

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6. Bound Charges vs Free Charges

Free Charges	Bound Charges
Move freely	Cannot leave atom
Found in conductors	Found in insulators
Cause current	Cause polarization

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7. Comparison: Conductor vs Insulator

Property	Conductor	Insulator
Electron mobility	High	Very low
Electric field inside	Zero	Non-zero
Response to E-field	Charge flow	Polarization

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Stage 0 – Page 3 Takeaway

• Electrical behavior depends on electron freedom
• Conductors allow charge flow
• Insulators polarize under electric field
• Polarization is crucial for dielectric problems

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Stage 0 – Page 3 Completed ✅