Electrostatics – Stage 0 (Foundation)
Chapter 1: Electric Charges & Fields – Page 2
1. How Does an Object Get Charged?
An object becomes charged when there is a transfer or redistribution of electrons.
Important Truth:
- Protons never move in ordinary processes
- Only electrons are transferred
JEE Core: Charging always means gain or loss of electrons.
2. Method 1: Charging by Friction
When two neutral objects are rubbed together, electrons are transferred from one object to another.
- One object loses electrons → becomes positively charged
- Other object gains electrons → becomes negatively charged
Key Observations:
- Both objects were initially neutral
- Charges produced are equal and opposite
JEE Trap: Friction does NOT create charge. It only separates existing charges.
3. Method 2: Charging by Conduction
Charging by conduction occurs when a charged object touches a neutral object.
- Electrons flow due to potential difference
- Both objects end up with the same type of charge
Important Results:
- Total charge is conserved
- Final charge depends on size and material
JEE Insight: After conduction, the neutral body always acquires the same sign as the charging body.
4. Method 3: Charging by Induction
Charging by induction occurs without physical contact.
Steps:
- Bring charged body near a neutral conductor
- Charges redistribute inside the conductor
- Ground the conductor
- Remove grounding, then remove charged body
Final Result:
- The conductor gets charged
- Charge is opposite to inducing charge
Advanced Concept: Induction proves that electric force acts at a distance.
5. Why Earthing (Grounding) Is Important
Earthing allows electrons to move freely between Earth and object.
- Earth acts as an infinite charge reservoir
- Potential of Earth is taken as zero
JEE Note: During induction, grounding decides magnitude and sign of final charge.
6. Conservation of Charge
Total electric charge of an isolated system remains constant.
Mathematically:
Σqinitial = Σqfinal
- Charge cannot be created
- Charge cannot be destroyed
- Only transferred
IIT Level: Conservation holds even in nuclear reactions.
Stage 0 – Page 2 Takeaway
- Electrons are responsible for charging
- Three methods: friction, conduction, induction
- Induction is contactless and powerful
- Charge is always conserved
Stage 0 – Page 2 Completed ✅
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