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Name: Class: Phv 2140 Date: ID: A May 24,2006 Physics 2140: Exam 1 Multiple Choice (7 points each) Identify the letter of'the choice that best completes the statement or answers the question. -- 1. Very large capacitors have been considered as a means for storing electrical energy. If we const~ucteda very large parallel-plate capacitor of plate area 8.0 m2using paper ( K = 3.7) of thickness 2.0 mrn as a dielectric, ~ 8.85 x 1VI2CZ/N.m2) how much electrical energy would it store at a plate voltage of 3000 V? ( E = (-a. 0.59 J b. 90 000 J N ; h c0&4 c. 9 0 J d. 45 000 J e. 9 000 J - / 1 3 1 ~ l oF 3 C- 4 - - -' 2. Which of the following best characterizes electrical conductors? a. poor heat conductors b. total electric charge is zero c. low mass density d. high tensile strength C e . electric charges move freely - 3. The resistance of a platinum wire is to be calibrated for low-temperature work. A platinum wire with resistance 3.000 R at 20°C is immersed in liquid nitrogen at 77 K (-196OC). If the temperature response of the platinum wire is linear, what is the expected resistance of the platinum wire at -196OC? c+,~.,~..~= 3.92 x 1 v 3PC)-] a. 1.768 n LNAT) b. 0.232 R So AT = -(9L0C - 2 3 2 c. 2.757 R d. 1.847 R 3n (I 3.9240 -2162 K = R, ( I R= = L A d'p ; r -'.(-zlaj 0,Y 60 -- R,= 202 uah.(. fi *y G ~ K 4. A point charge of +8.0 /.LCis located at the origin of a coordinate system and a second point charge of -4.0 pC is at x = 1.0 m. At what point on the x axis is the electrical potential zero? i s oePahk XCy, a. +0.25 m / $2 b. -0.33 m n/efF:t&*k/ f, 0 c. +0.75 m -0.25 m I -)c = kc +-I <bIw t x A' Ylj(P!J: 1 I r -X = O*&6 kb~?~ -- X = 8 1 ID: A - 5. If C = 5 1 pF, deterthine the equivalent capacitance for the combination shown. -- 6. In x-ray machines, electrons are subjected to electric fields as great as 6.0 x lo5 N/C. Find an electron's acceleration in this field. (me= 9.1 1 x I@]] kg, e = 1.6 x l@19C) F a. 3.6 x lo8 m/s2 . - mN 7. Two point charges, separated by 4.5 cm, have charge values of 2 p C and -9.0 pC, respectively. What is the e mutual force between them? (k, = 8.99 x lo9 N.m2/C2) c. d. e. 16N 3.6 x 1W8N 8.0 x 1@12N g = 2.-c c =L/.~C& rz ',EL = - ?PC PU Name: ID: A 0 -- 8. An electric car is electric motor "out of juice?" c. d. e. 3000km 2250 km 1500km ' = I J / i batteries with total energy storage of 5.0 x lo7 J. If the speed of 30 m/s, how far will the car go before it is ,Car fi'me i= UJEJ 2OOC)W c c l l o ~ - ga x= = wt'2 S r-5,. l h ~3b.t: s/c,oFJ2 3 3 0 7iac . bJki/e 2 S 0 d 0 dpr. 30 */5 2 a o o3 = b A E d . v-t hn / f z r 8 t 7'50 000 m 5 --==== 750 9. An electron is released from rest at the negative plate of a parallel-plate capacitor. If the distance across the plate is 7.0 mm and the potential difference across the plate is 3.0 V, with what velocity does the electron hit the positive plate? (me = 9.1 x l t 3 ' kg, e = 1.6 x l t I 9 C) 10. A charge, +Q, is placed inside a balloon and the balloon is inflated. As the radius of the balloon r increases the number of field lines going through the surface of the balloon: a. decreases as lir. b. decreases as l/r2. # o f ,$/A . stays the s a m e 2 IL_ b-1 L.OOY\ = FIUX a-d d. increases proportional to r. e. increases proportional to r2. S: LNW x ; Qeqc - AJ- G, -- CF/V - 11. If a 4000-W heater carries a current of 1 .OO A, what is the resistance of the heating element? a. 11.2R b. 42.8 R c. 10.0 n - J x ~ e~;lf Name: -- ID: A u 12. A metallic a. of I8 x 1 t 6 Q m . What is the resistance of a piece that is 90 m long and 160Q Short Answer (16 points) Please show your work in solving this problem. No credit will be awarded for answers without evidence of work supporting the answer 13. An electron with velocity v = 4.0 x lo6 mls is sent between the plates of a capacitor where the electric field is E = 900 Vlm. If the distance the electron travels through the field is 4.0 cm, how far is it deviated in its path when it emerges from the electric field? (me= 9.1 x I t ' ' kg, e = 1.6 x l t I 9 C) (u 4+4 cm-Y VVVVVV * ~ / ~ = f * i bc e l l 14 ,T;- h-~uc( 19 ~ LikPe- 4c-= O.OY*r. fa ,z ~ A y -At>