1. Phy2005 Applied Physics II Spring 2016 Announcements: Test 2 Wednesday, March 23 covers chs. 22-25, sections listed in syllabus + all material covered in class 2 practice tests posted on course Tests page. HOWEVER NOTE: --a) problems 9-12 deal with RLC, RL and RC circuits involving concepts not covered in this course. This is true on both S14 and S15 tests. --b) many of the problems on both tests are identical. this obviously doesn't help give more practice. --c) NOTE THEY DO NOT COVER CHAPTER 25, BUT YOUR TEST WILL! Review session in class TODAY in class + TODAY 6pm NPB 2205

2. Magnetism: magnets always have both N and S poles, as far as we know. Like poles repel, unlike poles attract: Magnetic interaction mediated by magnetic field B. Fields lines emerge from N pole, meet at S pole. Review Chapters 22-25 Magnetism

3. B Field B curls around wire with current I according to the “right hand rule” I I B FBFB F B = ILB Magnetic field (strength) [B] = [F/IL] = Ns/Cm = Tesla *1 Tesla = 10 4 gauss A wire placed in a perpendicular B-field experiences a sideways force! Force on wire in field

4. X X X X Switched I-direction here! DC motor: current loop in fixed magnetic field “commutator ring” “brushes”: electrical contact with moving commutator

5. For infinitely long solenoid with tight coils, inside B =  o nI (const.!) n: number of turns/m Note: for such a solenoid B=0 outside Solenoid: how to make a nearly constant magnetic field I B B B =  o I/(2  r) Field around a long, current-carrying wire

6. Faraday’s law: any time there is a time-changing magnetic flux through an area, there is an electromotive force (voltage) tending to drive current around the boundary of the area V ind = ( B / t ) rate of ch of B with time A - = -  /  t (rate of ch of  with time)  = BA  = B  A : magnetic flux A  is cross-sectional area  to field B  is field  to area

7. : The – sign in Faraday’s law  loop = 0  loop =  m +  s Current flows in a direction so as to oppose the change in flux it experiences (Lenz’s law) However, the induced current dies out due to a finite resistance in the conductor. B I ind B ind

8. Magnet always feels resistance to its motion. : practice w/ Faraday

9. t x -A x0x0 T (period) x = Asin(2  ft) frequency: f = 1/T angular frequency:  = 2  f = 2  /T “repeat time” 0T x rms AC current, voltage

10. Transformer Iron Core AC V NpNp NsNs V p /V s = N p /N s p=primary s=secondary

11. Use rms values of v and i for AC to evaluate average power. = v rms 2 /R = i rms 2 R = i rms v rms V ind = - n ℓ  /  t = - n ℓ A(  o n)  i/  t = - n 2  o A ℓ (  i / t) L: self inductance: V ind =-L  i / t L = geometrical quantity e.g. for solenoid, L= n 2  o A ℓ

12. V VcVc t V c = V (1 – e -t/RC ) t c = RC V c = V (1 – e -1 ) = 0.63 V t C =RC: time constant 0.63V e = 2.71828183 t V = V e -t/RC 0.37 RC R C +Q -Q + Charging a capacitor in RC circuit Discharging

13. y = sin(kx) Traveling wave with velocity v: y = sin{k(x-vt)} x Wavelength:  k period: T frequency: f = 1/T v = f James Clerk Maxwell (1861): a light wave (speed v=c=3x10 8 m/s) is a wave of electric and magnetic field!

14. E B EM wave

15. All electromagnetic waves such as light transmit energy. Light intensity = power flowing through the area / area (power density) [w/m 2 ]  R A  = A/R 2 [steradian] Total solid angle:  = 4  R 2 /R 2 = 4  (sr) Solid angle Intensity

16. “Polarization”: direction of electric field

17. For unpolarized light, a polaroid sheet reduces its intensity to half (sunglasses). θ I = I 0 cos 2 θ Intensity after polaroid Intensity before polaroid