PHYS 1120 Exam 1 NAME Student ID Section number and TA Name Exam Version 0001 Please do not open the exam until you are asked to Your exam should have 10 pages numbered E1 1 thru E1 10 This exam consists of 15 multiple choice questions worth 5 points each and a long answer section worth 25 points for a total of 100 points Write your answers in the space provided on each page for the written question Use the back of the page if needed Circle the correct letter for the multiple choice questions SHOW YOUR WORK ON THE WRITTEN QUESTIONS Full credit will be given only for the correct answer accompanied by your reasoning PLEASE 1 2 3 4 Print your name on each page in the space provided Print your student Identification Number on the page above Bubble your name ID and exam version number on the bubble sheet provided Write the name of your TA neatly in the big blank space at the bottom of the bubble sheet Our TA s names are Charles Bailey Jeremy Brown Craig Hogle Daniel McKinnon and Youngwoo Yi I recommend Don t waste time erasing on the written problems Just put a line through defective reasoning Ask for more paper if needed At the end of the exam check that you have completed all the questions By handing in this exam you agree to the following statement On my honor as a University of Colorado Student I have neither given nor received unauthorized assistance on this work Signature Possibly useful information k 9 0x109 N m2 C2 basic charge unit 1 6x10 19 C 0 8 85x10 12 C2 N m2 G 6 7x10 11 N m2 kg2 Good luck Spring 2008 E1 1 First Midterm PHYS 1120 Exam 1 NAME Circle the closest answer and Bubble in questions 1 15 ON YOUR BUBBLE SHEET The gravitational force that a spherical body of mass M1 feels from a second spherical body of mass M2 when their centers are separated by a distance r is attractive and has a magnitude given by This force is very similar in form to Coulomb s Law for the force between static point charges 1 We can ignore static electric forces when calculating the motion of planets around the Sun because A electric forces drop to nearly zero much more quickly with distance than gravity forces B gravity forces are intrinsically larger than electric forces C no electric forces are actually an important part of understanding planetary orbits D planets and the Sun are electrically neutral so the electric forces are very small E planets and the Sun are not point particles so the electric forces do not follow Coulomb s Law 2 A plastic rod has an initial charge of 3 mC The rod is rubbed with a neutral cloth After the rubbing the rod has a final charge of 6 mC A Conservation of charge requires that the cloth has a 6 mC net charge B Conservation of charge requires that the cloth has a 3 mC net charge C Conservation of charge requires that the cloth has a 3 mC net charge D Conservation of charge requires that protons moved to the cloth E Conservation of charge requires that both objects remain neutral 3 A charge of 7 microC is located 3 meters from a charge of 3 milliC The electric force on the 7 microC charge from the 3 milliC charge is A A repulsive force of 42 N B An attractive force of 63 N C An attractive force of 21 N D An attractive force of 21 N C E The force is zero Spring 2008 E1 2 First Midterm PHYS 1120 Exam 1 NAME The following two questions refer to this situation Two identical negatively charged particles each have mass m and charge Q The two particles are placed a distance R apart in empty space and are released from rest Each particle feels only the Coulomb force due to the other particle There is no gravity in this problem Q Q m R m 4 The initial magnitude of the acceleration of each particle immediately after release is A B C D E none of the above 5 As the particles continue to move after their release the magnitude of the acceleration of each particle A decreases B increases C stays the same D initially decreases but then increases 6 The electric field 4 cm from a point charge of 3 C is A 16 9x1012 N C pointing towards the charge B 6 8x1011 N C pointing away from the charge C 6 8x1011 N C pointing towards the charge D 16 9x1012 N C pointing away from the charge E The field is zero Spring 2008 E1 3 First Midterm PHYS 1120 Exam 1 NAME The following three questions refer to this situation Two particles one with positive charge Q and the other with negative charge 2Q are located on the x axis as shown below The three questions below ask about the magnitude of the electric field on the x axis in the three regions I some finite distance to the left of the two charges anywhere but infinity II somewhere in between the two charges and III some finite distance to the right of the two charges anywhere but infinity I II Q III 2Q 7 In region I the electric field A is everywhere non zero and pointing right B is everywhere non zero and pointing left C can be zero at some location 8 In region II the electric field A is everywhere non zero and pointing right B is everywhere non zero and pointing left C can be zero at some location 9 In region III the electric field A is everywhere non zero and pointing right B is everywhere non zero and pointing left C can be zero at some location 10 A flat rectangular surface has an area of 2 5 m2 An electric field of 6 N C is directed at an angle of 63 degrees to the surface normal vector as shown The electric flux through the surfaces is A 15 N m2 C B 6 8 N m2 C C 6 8 N m2 C D 13 4 N m2 C E Flux is zero Spring 2008 E1 4 First Midterm PHYS 1120 Exam 1 NAME The following three questions refer to this situation A point positive charge q 2 C is surrounded by a charge neutral spherical metallic shell as shown in the figure The shell has an inner radius of 1 5 meters and an outer radius of 2 5 meters The positive point charge causes a rearrangement of the charges in the metal leading to some separation of negative and positive charge as shown 11 At point A 1 meter from the point charge the electric field A is zero due to Gauss s Law B is 1 8x1010 N C in magnitude C is zero because metals screen electric fields D is 3 6x1010 N C due to superposition of the point charge and neg surface charge 12 At point B …
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