exam1_2008

exam1_2008 - Physics 4 February 26, 2008 Exam I Calculators...

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Unformatted text preview: Physics 4 February 26, 2008 Exam I Calculators may be used, but no books or other written materials. Answer all four questions and show the steps leading to your answers. Credit will be given based on evidence of your understanding of the material. Be sure to express all quantities in proper units. Potentially useful information l E: 1 ‘1; l 47:50:" 1 Gauss’ Law: Cf}? A d2 = QM, / 50 _. A F = qE U12 : 1 (119‘2 V m 1 i 47:80 r12 47750 r 2 4 3 surface area of a sphere = 47W ; volume of a sphere a 3727' surface area of a cylinder = 211: r L (side) +27rr2 (both ends); volume of a cylinder = TE r215 r 4. F = 11155 1 =9.0X109]\;’-mz/C2 ; 5'0 =9.0x10-i2C2 [Nimz 47:30 e:1.6x10"9C 1 Ceq,pamfl‘el = C1+C2 +--- : i+i+ Ceq,ser1'es C1 C2 1 ch,series =R1+R2+-v- —:i+._l_+'" Reg, parallel R; R2 V = [R i: ioewc, charging a capacitor Q: CV b —. A. V. 4/}, = [15 all U = lCIfl J u __ flEz 2 2 1. Five short questions. Answer briefly (a sentence or two) (2 pts each): a) Rain drops are larger during a thunderstorm than the drops of rain falling from ordinary rain clouds. Briefly explain why. [Hintz large electric fields are present inside thunder 3 Clouds] V b) In a lecture demo we added charge Q and measured the potential difference V0 across a parallel plate capacitor. Then, with the capacitor disconnected from the electrostatic generator, we doubled the separation between the plates and noted the potential difference V. Did it change from V0 and if so, what was its new value? Explain briefly. c) A conducting spherical shell initially has a charge of IOuC. A charge of ~10uC is inserted inside the shell without touching it. i) What are the charges on the inner and outer surface? ii) If the -l 011C is deposited onto the inner surface of the shell, what will be the resulting charges on the Shell’s inner and outer surfaces? (1) The figure below shows two situations in which two charged particles are fixed on a line. In which situation is there a point to the left of the particles where an electron would experience no net force? Explain briefly. ———-——o———~——0—— ———--——e———e——~ write data ‘Q/M: +3fic (t) (it) e) If we have two charges in a line (as in the above question) and if there is some point on the line where the net force on an 3Id charge is zero, will the electric potential necessarily also be zero at this point? Explain briefly. 2. Two parts (5 pts each) a) A spherical insulator of radius R has a total charge Q spread uniformly throughout it. i) At some distance r from the center of the sphere (r > R) what is the electric field E? ii) What is the field E for r < R? b) A large flat insulating sheet of thickness d has charge spread uniformly throughout with a volume charge density p. At some distance outside the sheet, what is the electric field E? (direction and magnitude) / 1‘ AL_____ wt 3. Two parts (5 pts each) a) As Show in the figure, a l uF capacitor C1 is charged by a 24V battery. i) After the capacitor C1 is fully charged, what is its charge Q0? C The switch is thrown to the right, disconnecting the battery and instead i ‘1 connecting capacitor C1 to two other capacitors C2 (2uF) and C3 (4uF). -—--‘ Ci _____...- C3 ii) Now, what are the charges and the potential difference on each capacitor? b) Consider the circuit shown below. I ‘51 H ov i) With switch S open, what is the potential difference Vab? \m f p 637. NW ii) After the switch is closed, what is Vab? 4. Two parts (5 pts each) a) In the circuit below, the currents are as shown. What are the battery emfi'g’? (:2? J b) In the circuit below, What is the power delivered to each resistor R1 and R2 ? .g/qu IQFQQJ?’ flea—JFK'JVW ...
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This note was uploaded on 11/02/2010 for the course PHYS 0030 taught by Professor Cutts during the Spring '07 term at Brown.

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exam1_2008 - Physics 4 February 26, 2008 Exam I Calculators...

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