Electrostatics
Coulomb’s Law: F = k * (q1 * q2) / r²
k = 1 / (4πε0) = 9 × 10⁹ N·m²/C²
F = force between point charges q1 and q2 separated by distance r
ε0 = permittivity of free space = 8.854 × 10⁻¹² C²/(N·m²)
Electric Field (E): E = F / q
Electric field due to point charge: E = k * Q / r²
Direction: Away from positive, towards negative charge
Electric Potential (V): V = k * Q / r
Work done to bring unit positive charge from infinity to a point
Potential difference: V = Vb - Va = W / q
Relation between E and V: E = -dV/dr (for uniform field: E = V / d)
Superposition Principle: Net E at a point = vector sum of fields due to all charges
Electric Dipole:
Dipole moment: p = q * 2a (2a = separation between charges)
Field on axial line: E = (1 / 4πε0) * (2p / r³)
Field on equatorial line: E = (1 / 4πε0) * (p / r³)
Potential at point along axial line: V = (1 / 4πε0) * (p cosθ / r²)
Flux & Gauss’s Law:
Electric flux: ΦE = E · A cosθ
Gauss’s law: ΦE = q_enclosed / ε0
For spherical symmetry: E = (1 / 4πε0) * Q / r² (same as Coulomb’s law)
Capacitance:
C = q / V
Parallel plate: C = ε0 * A / d
Energy stored: U = 1/2 * C * V² = 1/2 * q * V
Series & Parallel Combination:
Series: 1/Ceq = 1/C1 + 1/C2 + ...
Parallel: Ceq = C1 + C2 + ...
Force between plates of capacitor: F = (1/2) * Q² / (ε0 * A)
TERMINAL JOINT
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Terminal Joint
