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Phy 102 2007 Exam 1

# Phy 102 2007 Exam 1 - QOQgFojTi c/éA/Swm Two point charges...

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Unformatted text preview: QOQgFojTi c/éA/Swm Two point charges, Q1 = - 4.00 p0 and 02 = +6.00 110 are placed on a 300° - 60.0“ right triangle of a small side of 2.00 cm and a hypotenuse of 4.00 cm. [1] The x-component of the electric field at point P is a) — 11.3 MNIC b) .— o.7e MM: @195 MNIC d) — 1.95 kN/C e) + 11.3 MNIC [2] The y-component of the electric ﬁeld at point P is ' 89124 MNIC b) 146 MNIC c)113 MNIC d) 124 kNlC e) — 146 MNIC [3] Electric ﬁeld lines contact a conducting surface a parallel to that surface @erpendicutar to that surface - never — they don’t contact the surface 0) at random angles, depending on the problem d) only if the surface has a net positive charge [4] Two point charges of + 600 pt) and —12.0 “C are separated by a distance of 20.0 cm. A +7.00 uC charge is placed midway between these two charges. What is the electric force acting on this charge because of the other two charges? Zero b) 4.53 N directed towards the negative charge ,3 4.53 N directed towards the positive charge 53 N directed towards the negative charge xv 453 N directed towards the positive charge [5] Dr. Zane's husband is related to which famous person from the Revolutionary War? . i213: “:21... FE g, -+_ ,. w Vi. r. I s- a 2 [6] The length of a certain wire is doubled while its radius is halved. What is the change of the resistance in this wire? a) It stays the same. 9 is increased by a factor of 8 c) It is reduced by a factor of 8 it is reduced by a factor of 2 a) it is reduced by a factor of 4 [7] The electric potential at x; = -8 m is w4000 V. and at x1 = 2 m is +1000 V. The electric field, E is ‘ a) SOOV/mh’i b) (—SOOV/mﬁ c) (400V/m)i d) (—400V/m)5i e) None of these. [ 8] A 0.24-uF capacitor is charged by a 12-V battery. After being charged, the capacitor is connected to a small electric motor that is 100% efﬁcient. How large a mass can this motor lift to a height of 6 cm? “9 b) - HQ 0) 290 “9 W .ie) none of these x} i J _ [ 9] The energy stored in a capacitor is stored y the battery b) indeﬁnately in the dielectric d) the electric ﬁeld between the plates e) none of these [10] Three charges are situated at the corners of an equilateral triangle of side d as shown below. How much work must be done to move them inﬁniter far from each — 'L\5' other? +7Q2 —7Q2 —7Q2 332 3) d2 0) zero d) [11] A “perfect” or “ideal” ammeter would have what resistance value and be connected in the circuit in what way? — Al [12] A ‘lOO—W light bulb is plugged into a household wall outlet (120 V). The resistance of the bulb is @440 [13] The emf of a battery is 9 V. When the battery is connected in series with a 35-0 resistor, the current is 0.25 A. What will a voltmeter measure across the battery terminals when current is ﬂowing in the circuit? a) 1.2 0 b) 0.12 0 d) inﬁnite a) zero a) 9 V @025 V c) 35 V d) 2.25 V e) 8.75 V [14] The equivalent resistance between points A and B is c) 4.00 0 @338 Q a) 26.5 o b) 0.540 0 e) 0.900 a [15] Kirchhost Rules state that a) V = IR b) The algebraic sum of the potential differences around a closed loop is zero. The algebraic sum of all currents meeting at a junction point (node) is zero. Gd oth b and c. Both a and b. [16] Consider the following cirouit: a) Find the current through each resistor. b) Find the potential at points A and B. [17] A point charge, Q, is at the center of a hollow, neutral conducting shell as shown in the picture. Hint: there are no numbers involved, equations only! 3) Using Gauss’ Law, calculate the magnitude of the electric ﬁeld at distances r1, r2, and r3. b) Calculate the work required to move a charge of -Q from RA to R3. Is this work positive or negative? Prove it! c)- Calculate the work required to move a charge of -Q from point C to point D. Uh: :. “NU-V’L - (i Wv‘vw L _. D P C. H \I rum to -V\ h-Ck.‘ -\/_ :/._\_:_;.'/,_\ phch c 8 ml w. cum l "Dr .7 cum, Two point charges, 01 = - 4.00 “C and Q2 = +6.00 uC are placed on a 30.00 - 60.0” right triangle of a small side of 2.00 cm and a hypotenuse of 4.00 cm. 4x +y Q16: [1] The x-component of the electric ﬁeld at point P is a) — 11.3 MN/C b)— 0.78 MN/C «an. 0) u 19.5 MNIC d) — 1.95 kN/C e) + 11.3 MNIC alga art“ lel A. 5 Ex = Eix +E2x = (cos30°)(—x)+0 (diplz (9x109 N - m2 /C2 l(—4.00x10“’C)l _ ((0.04m)2 E X (cos30°)(—>7:) = _19.5MN/c [2] The y-component of the electric field at point P is M) 124 MNIC b) 146 MNIC c)113 MNIC d) 124 kNIC e)#145 MN/C E _E E _ ' o F ‘ 2 A y H 1y + 2,. — 2 (811130 )(—Y)+ 2 (W) (dip) (dzp) ( j j (—4.00x10‘6C)| l(6.00x10'6C)l Ey =(9xlO)N-m"/C" —2(sin30°)(—§)+—2(\$’) ((0.04 m) ((0.02 m) 133/ =124 MN/C [3] Electric field lines contact a conducting surface a) parallel to that surface -- b) perpendicular to that surface 0) never — they don’t contact the surface d) at random angles, depending on the problem e) only if the surface has a net positive charge [4] Two point charges of + 600 p0 and —12.0 [10 are separated by a distance of 20.0 cm. A +7.00 uC charge is placed midway between these two charges. What is the electric force acting on this charge because of the other two charges? a) Zero b) 4.53 N directed towards the negative charge 0) 4.53 N directed towards the positive charge ..—.d) 453 N directed towards the negative charge e) 453 N directed towards the positive charge See practice exam multiple choice solutions. [5] Dr. Zane’s husband is related to which famous person from the Revolutionary War? Benjamin Franklin [6] The length of a certain wire is doubled while its radius is halved. What is the change of the resistance in this wire? a) it stays the same. """' b) It is increased by a factor of 8 c) It is reduced by a factor of 8 d) It is reduced by a factor of 2 e) It is reduced by a factor of 4 ' R _le _le R _pL2 _—_ 2 2 _ _ 2 _ 2 _ l 2 [7] The electric potential at xi = -8 m is -4000 V, and at Xf = 2 m is +1000 V. The electric field, Eis a) (SOOV/mﬁ —--b) (—SOOV/mﬁi c) (400V/m))’t d) (—400V/m)5€ e) None of these. a V —V +1000V— #4000V E= AV— ( 2 ')= ( ( D: 500W =( 500V/m)5‘< as _ (32—3) (2miw(#8m§<)) (10mg [8] A 0.24-uF capacitor is charged by a 12—V battery. After being charged, the capacitor is connected to a small electric motor that is 100% efficient. How large a mass can this motor lift to a height of 6 cm? a) 29 pg b) 2.4 pg 0) 290 ng d) 24 ng a-ue) none of these l 2 CV2 _ (0.24x10'61:)(12V)2 Zgh 2(9.8m/52)(0.06m) mgh = CV2 =29mg m: [9] The energy stored in a capacitor is stored a) by the battery b) indefinately c) in the dielectric .— d) in the electric ﬁeld between the plates e) none of these [10] Three charges are situated at the corners of an equilateral triangle of side (1' as shown below. How much work must be done to move them infinitely far from each other? ‘Q ‘20 +3Q 3) +3?” b) #31522 0) zero d) _7§2 .— e) +752 w = wAU : _k[(—Q)(+3Q) + (—QX—ZQ) + (—ZQ)(+3Q)] d d d w z z +714?) = (my) d d d [11] A "perfect" or "ideal" ammeter would have what resistance value and be connected in the circuit in what way? 0 ohms, connected in series [12] A 100-W light bulb is plugged into a household wall outlet (120 V). The resistance of the bulb is a) 1.2 0 b) 0.12 0 —— c) 144 Q d) infinite e) zero p=_ _, R:%:m 100W =144Q [13] The emf of a battery is 9 V. When the battery is connected in series with a 35-0 resistor, the current is 0.25 A. What will a voltmeter measure across the battery terminals when current is ﬂowing in the circuit? a)9 v b)0.25 v 0) 35V d) 2.25v ‘3) 8.75v V=S-Ir —> 5=chq=I(R+r) —> rzé—Rz 9V I (0.25A) v = 9V — (0.25 AXIQ) = 8.75V —3SQ=1Q [14] The equivalent resistance between points A and B is a) 26.5 o b) 0.540 0 c) 4.00 o a—d) 0.838 n e) 0.900 n [15] Kirchhost Rules state that a) V = lR b) The algebraic sum ofthe potential differences around a closed loop is zero. c) The algebraic sum of all currents meeting at a junction point (node) is zero. --d) Both b and c. e) Both a and b. [16] Consider the following circuit: a) Find the current through each resistor. b) Find the potential at points A and B. Ii '3 3) Node Eqn: 11 = 12 +13 Loop#1 : Outer loop fromA(cw)back toA —I3(6Q)—6V — l,(8§2)+12V— 11(4Q) : 0 Dropping the units and cleaning up, we get: 21, +13 =1 Loop # 2 : Left loop item A back to A —12(ZQ) —~ II(BQ)+12V— 11(4Q) : 0 611 +12 = 6 Substituting the node equation in the above for I2 : 611441143): 6 711—13 = 6 Add this to the lst loop eqn. 911:7 —> l1=—;-A=0.78A Sub this into the 2nd loop equation: 6(0.78A)+I2 = 6 I2 = 1.3A Using the node eqn.: 0.78A=1.3A+l3 I3 = -0.54A 12V —l,(4§2) = VA =8.9V b ) VA —I3(6Q)—6V: VB :6.IV [17] A point charge. 0, is at the center of a hollow, neutral conducting shell as shown in the picture. Hint: there are no numbers involved, equations onin a) Using Gauss‘ Law, calculate the magnitude of the electric field at distances r1, r2, and r3. to) Calculate the work required to move a charge of -Q from RA to R3. Is this work positive or negative? Prove it! 0) Calculate the work required to move a charge of -Q from point C to point D. a) ELA = Zancloscd 0 —> For a spherical Gaussian surface, EU.) : Zanclojsed 4naur“ + + * + — + + E(rl):__. 02 E(r2)= Q 13(13): M: Q? 47:8an 4115805 4118“; 4112805“ +kQ +kQ 2 1 1 ) ( Q)( A B) Q[ RA RB] Q [RA RB] RA < RB :> — > 0 We must DO work to push a negative charge away A B from a positive charge! 0) We move from point C to point D along an equipotential surface and so zero work is done. ...
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Phy 102 2007 Exam 1 - QOQgFojTi c/éA/Swm Two point charges...

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