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PH HY 1033 Fall 2011 Exam #3 3 Practice In class (11 hr. 40 min.. ending 4:40 0 pm) Ihas Oct. 27 You aree allowed to co onsult one 8.5””x11” sheet off paper with an nything writtenn on it in your own hand, and d to use a calculator, ruler, and a pencils or pens Do not n violate the UF honor cod de. Answers without w the reqquired justificaation or explan nations will bee counted wrong, wers will only clarify the exa am even iff they are corrrect. You mayy quietly ask me any question after raisi ng your hand,, but my answ questio ons. Good luckk! n air) = 3x108 m/s m c(light in c(sound in classroom aair) = 341 m/s h = 6.6x10‐34 J/Hz n(water) = 1 1.33 Q(electron) = 1.6x10‐19 Cou ulombs 1. What field d or fields, if any, compo ose an electromagnetic w wave? Electric and Maggnetic. 2. Does a chan nging magnettic flux always produce an induced fieldd, or only if th here is a cond ductor presen nt? Always. p is stattionary in a magnetic m field d B. What forrce does it feeel from this field? 3. A charged particle None. It is stationary relative to the field. f wing in a possitive direction in a vertica l wire. Use yo our right hand d to 4. An electric current is flow determine what the maggnetic field produced lookks like and draaw it in a pictture, showingg the direction off the flux. s a situation involvingg Faraday’s Laaw. 5. The figure shows he bar magnett around so the S pole is to o the left, andd we move ou ur hand 6. If we flip th AWAY from m the coil of wire w (moving to t the right), what else, if anything, will change in the picture an nd why? Nothing elsse changes, since the CHAN NGE in flux will be the sam me. 7. What is Bre ewster’s angle e for light reflection off a clear c lake? taanӨ = n = 1.333 so Ө = Inverse (tan 1.33)) = 53° 8. Which pole e of the Earth’’s magnet is near n the north geographicc pole? South.. 9. Does a chan nging magnettic flux produce an electricc current if thhere is no con nductor preseent? Explain. No, there must m be an ele ectrically conducting circuit to carry thee flow of elecctrons. 10 0. You rub a plastic p straw, charging it, and wave it up p and down 3 times per seecond. What is the frequency of E‐M radiation produced? Show calculatio on. T=1/3 secc so f=1/T=3 H Hz 11 1. In what parrt of the E‐M spectrum is the t radiation in the proble m above? Veery long waveelength radio waves. 12 2. The work fu unction ф is the amount off energy it takkes to pry an electron from m a metal. For copper ф = 4.5 eV. What W is the lo owest frequen ncy light whicch can free an n electron fro om copper? ‐19 ‐19 ‐34 155 1.6x10 Joules and f=E/h so f=4.5x1.6xx10 /6.2x100 = 1.2x10 Hz E=фq=4.5x1 13 3. What is the e wavelength of the photon in problem above? Show w you equations. 8 15 ‐7 λ=c/f=3x10 /1.2x10 =2..5x10 m=250 0nm 14 4. What part of o the E‐M sp pectrum is the e photon in problem abovee? Show you ur logic in casee you got #7 w wrong. UV 15 5. What physiical property does not change when a light wave entters a block o of clear glass ffrom air? f 16 6. (2 pts) Which bends mo ore on diffractting, red or blue light? Whhich bends leess on refractiing, red or blu ue light? Red; red 17 7. (5 pts) You take the follo owing data on n the photo‐e electric effectt: λ = 400 nm V = 2.0 voltts V = 1.5 voltts λ = 530 nm V = 1.2 voltts λ = 670 nm V = 0.9 voltts λ = 900 nm Make a neaat graph of E(photon) vs. f((photon). Use your ruler tto get the scaales correct, in n Joules (y‐axxis) and Hz (x‐‐ axis). e of the best straight–line fit to the plottted points in n units of Joule‐sec? Extra creditt (2 pts): Whaat is the slope 3.40E-019 Photon Energy in Joules 3.20E-019 3.00E-019 SLOPE=4.2E-34 J-s note: h=6.2E-34 J-s 2.80E-019 2.60E-019 2.40E-019 2.20E-019 2.00E-019 1.80E-019 1.60E-019 1.40E-019 1.20E-019 3.00E+014 4.00E+014 5.00E+014 6.00E+014 7.00E+014 Photon Frequeny in Hz 8.00E+014