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Unformatted text preview: PHYS 122. EXAM II November 6, 2008
Prof. S. M. Bhagat Name: 50; (4 T(ION (Sign in ink, print in pencil) Notes 1) There are six (6) problems in this exam. Please make sure that your copy has all of them. 2) Please showyour work indicating clearly what formula you used and what the symbols mean. Just writing the answer will not get you ﬁlll credit. In stating vectors give both
magnitude and direction. 3) Write your answers on the sheets provided.
4) Do not forget to write the units. 5) Do not hesitate to ask for clariﬁcation at any time during the exam. You may buy a
formula at the cost of one point. Take Care! God Bless You! Nm2 _ T¥—m
ke=9><109 C2 ,,uo=472xlO7——A—
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50 —9x10 [n
Mass of proton mp =1.6x10‘27kg Mass of electron me = 9 x10'“ kg Elementary Charge e ='1.6 x10"9 Problem 1. A conducting sphere of radius 2m is placed with its center at r= 0 and carries a charge of
~100 yC. Calculate the E ~ﬁeld at F 1.9m and r= 2.1m. (16) Problem 2a Why is there a minus sign on the right side of the equations
AP: —I_75 o A_.S
AV= —E a Q
where AP is change in potential energy and AVis change in potential. (2, 2)
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In order to place a charge Q on a capacitor C one has to put in 2— Joules of work. Where
does this energy go? Why? (0 l if“,
'T'W‘S .eM W V5 ﬂag; Problem 2c In the circuit shown which capacitor has i) the highest potential difference and ii) which capacitor has the smallest charge? Why? > (8)
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Vera. V1: A?" £6, 9h Pia/We Va) man» So Problem 321 Discuss the physical bases of Kirchhofi’s Rules. (3,3)
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a £3 meg/ad JA 4}; a, (Mme/ham E rm, = 211‘». Problem 3b In the circuit shown, when you close the switch which resistor has i) the highest current and lot/2, (1°) ii) the lowest current? Why? Problem 4a In at RC circuit, (seen below) the characteristic time is T = RC. Why do both R and C appear
in T? (6) awWZHS w Wm #
EA 1:, lam/5a 2 37AM mm.
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a =cs MW c/W’“
t} .2 . Problem 4b Shown are two RC circuits. If both switches are closed at the same time which capacitor potential will reach 5 volts ﬁrst
ifi) a, = $2 =10Vorii).c:1=9V,e32 =10V ? Why? (10) M5. Two parallel plates have uniform g =100N/cf1 between them. Introduce a particle of
charge ~q traveling at y =104m/s J7: . What 13 ﬁeld, magnitude and direction, would you apply so that the particle goes through the plates undeﬂected. (16)
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6:4,”, 2 Problem 6 a) A moving charge in a g ﬁeld goes on a circular path. Why is its kinetic energy constant?  (5)
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ka 0w W5 MW 5" ‘0". Camrﬁf («PAW (<39 EweV56" b) What is the difference between a Coulomb E —ﬁeld and a Non—Coulomb E ~ﬁeld? (5)
» —> Problem 6 (cont’d! c) What is a Conservative Force? ‘ ad (4)
A} W ,5 WM‘M 1
m a. :52 I. I L 7— (ﬁg. ‘0' l maL—{f (at? «~6— ‘ZM rpm. (1) How do mass (m) and charge (q) help you to discover the Gravitational ﬁeld (Q F) , the
E ﬁeld and the 12 ﬁeld? _ (6) ...
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 Spring '16
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