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Lesson
Electric Charges and Fields — Complete Lesson
? Electric Charge
Charge is a fundamental property of matter. Two types: positive (+) and negative (-).
Quantisation of charge: q = ne, where e = 1.6 × 10?¹? C (charge of electron)
?? Coulomb's Law
F = kq1q2/r²
where k = 1/(4pe0) = 9 × 10? Nm²/C²
where k = 1/(4pe0) = 9 × 10? Nm²/C²
?? Electric Field
E = F/q0 — force per unit positive test charge. Unit: N/C or V/m.
For a point charge: E = kQ/r² (directed radially outward for +ve charge).
?? Electric Field Lines
- Start from +ve charge, end on -ve charge
- Never intersect each other
- Closer lines = stronger field
?? Gauss's Theorem
? E? · dA? = q_enclosed / e0
Total electric flux through a closed surface equals the enclosed charge divided by e0.
Total electric flux through a closed surface equals the enclosed charge divided by e0.
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MCQ Practice
Electric Charges & Fields — MCQ Practice
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Memory Trick
Electric Charges and Fields — Mnemonic
Mnemonic 1: Types of Electric Charges ⚡️
"P+ N- = Friends, Opposites Attract!"
- P+ = Positive charge (like Proton)
- N- = Negative charge (like Electron)
- Remember: “P+ N- = Friends” because opposite charges attract each other.
Mnemonic 2: Coulomb’s Law Formula 🧲
"F = k Q₁ Q₂ / r², “Khaana Qabool, Door Door!” 🍲
- F = Force between charges
- k = Coulomb constant (like 'Khaana' for constant taste)
- Q₁, Q₂ = Magnitudes of charges
- r² = Square of distance (distance squared means force decreases fast)
- Hindi phrase “Khaana Qabool, Door Door” helps remember Force ∝ 1/r² and proportional to charges.
Mnemonic 3: Electric Field Direction 🔄
"Positive Pushes, Negative Pulls!"
“Plus hai toh Push, Minus hai toh Pull!”
- Electric field direction is away from positive charges (push)
- Electric field direction is towards negative charges (pull)
- Hindi phrase “Plus hai toh Push, Minus hai toh Pull” makes it easy and fun to recall.
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