Charge
Coulomb's law, force of attraction/repulsion F = kQ₁Q₂/r² Q₁ and Q₂ are the charges in coulombs F is force in newtons r is separation in meters k = 8.99e9 Nm²/C² k = 1/(4πε₀) where ε₀ = 8.8542e-12 F/m = permittivity of space (F/m) in presence of dielectric, that is modified to F = Q₁Q₂/(4πε₀εᵣr²) or F = kQ₁Q₂/(εᵣr²) εᵣ is dielectric constant (vacuum = 1) Potential energy between two charges, in Joules U = kQ₁Q₂/r Q₁ and Q₂ are the charges in coulombs r is separation in meters k = 8.99e9 Nm²/C² between three charges it is U = (kQ₁Q₂/r₁₂) + (kQ₂Q₃/r₂₃) + (kQ₁Q₃/r₁₃) (assume – for unlike charges) Charge moving in an electric field E = QV 1 coulomb moving thru a 1 volt change = 1 J Electric field The strength or magnitude of the field at a given point is defined as the force that would be exerted on a positive test charge of 1 coulomb placed at that point; the direction of the field is given by the direction of that force. E = F/Q = kQ/r² Q = F/E F = QE in Newtons/coulomb OR volts/meter k = 1/4πε₀ = 8.99e9 Nm²/C² 1 C = 6.242e18 electrons 1 electron charge = 1.602e-19 C Potential from a charge is V = kQ/r in volts k = 1/4πε₀ = 8.99e9 Nm²/C² r is separation in meters q is charge in coulombs Energy in a particle E = hf, where h = Plank's constant 6.626e-34 Js E = hc/λ E is the energy of the particle in Joules f is frequency, λ is wavelength in meters |
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