PHYS 422 Lecture 5 EM Theory I

PHYS 422 Lecture 5 EM Theory I - Electromagnetic Theory,...

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lectromagnetic Theory, Electromagnetic Theory, Photons, and Light I
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Classical EM Waves versus Photons he energy of a single light photon is =h The energy of a single light photon is Eh ν The Planck’s constant h = 6.626×10 -34 Js isible light wavelength is 05 J 10 4 19 1 × = = c h h E Visible light wavelength is λ ~ 0.5 μ m Example: laser pointer output power is ~ 1 mW umber of photons emitted every second: number of photons emitted every second: photons/s 10 5 . 2 photon 0 J/s 10 15 19 3 × = = P J/photon 10 4 1 × E Conclusion: in many every day situations the quantum nature of light is not pronounced and light could be treated as a classical EM wave Quantum uncertainty. Example: throw a single coin, it will fall either heads or tails up, unpredictable but with 10 15 coins - can predict result with high precision
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Basic Laws of Electromagnetic Theory lectric field Coulomb force law: Electric field 2 2 1 0 4 1 r Q Q F F πε = = G electric permittivity of free space Q 1 Q 2 F F Black box Q E F 1 = G G Interaction occurs via electric field r r Q E ˆ 4 1 2 2 0 = G Electric field can exist even when charge disappears (annihilation in black box)
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Basic Laws of Electromagnetic Theory Magnetic field Moving charges create magnetic field 0 ˆ r v q × G G μ The Biot-Savart law for permeability of free space 2 4 r B = π moving charge Magnetic field interacts G G with moving charges: B v q F magnetic G × = Charges interact with both fields: B v q E q F G G G G × + = (Lorentz force)
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araday’s Induction Law Basic Laws of Electromagnetic Theory Faraday’s Induction Law 1822: Michael Faraday Changing magnetic field can result in curly electric field dt d emf M Φ = normal
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This note was uploaded on 03/23/2011 for the course PHYS 422 taught by Professor Staff during the Spring '08 term at Purdue University-West Lafayette.

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PHYS 422 Lecture 5 EM Theory I - Electromagnetic Theory,...

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