RI-1 Phys2020 Exam 3 Review: Magnetism • Currents cause magnetic fields (B-fields) • BBFFqvBsin qv⊥== θ =GBFG "right-hand-rule" • When both E-field and B-field are present: Ntot E BqEFF=+GGG• B-field due to long straight wire: 0IB 2rµ=πB=+GGGB • "modified right-hand rule" point thumb in direction of straight thing, fingers curl in sense of circular thing. • B-field is a vector: BB tot 1 2 • Force on a current-carrying wire: Non wireif I, B FILBsin IL⊥= θ =• parallel currents attract; anti-parallel currents repel • solenoid or permanent magnet Faraday's Law • An emf (= battery voltage) is caused by a changing magnetic flux: (N loops)Nt∆Φ= −∆E ( whereΦ is the flux through 1 loop) magnetic flux Φ BA⊥= net atomic current on rimuniform B(out) Side View: atomic current on rim, B-field enters like solenoid B-field comes End View: out of "North" end "South" endRI-2 • Lenz's Law: Iinduced creates Binduced in direction that opposes change in flux. • Motors and generators • Eddy current forces always oppose the motion • Transformers only work for changing voltages (AC voltages) out S Sin P PVVVVN==N Pout ≅ Pin ⇒ IS VS = IP VP ⇒ SPPPSIVNIV==SN EM Waves • Light is an electromagnetic wave which is created by accelerating electric charge. • , EM spectrum (radio, visible, IR, UV, etc) f c speed of light = constantλ == • 2power Pintensity (W/m ) = , Iarea A=2 Ray Optics • Snell's Law: , where index of refraction = 11 2nsin nsinθ = θcnv= • total internal reflection, critical angle θC : ns o1c 2 21in n sin(90) nθ ==• Converging and diverging lenses , focal length f < 0 f > 0 • Ray diagrams, image formation, real vs. virtual images • Camera vs. eye • image/object math: oi11fd=+1d , iioohdMhd≡
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