Circle the closest answer and Bubble in questions 1 15 ON YOUR BUBBLE SHEET 0 Bubble in your name your correct Student ID number onto your bubble sheet If you leave your ID number blank we will deduct a point from your exam score If you are not certain about it please see and instructor To ensure accurate grading bubble your Exam version number 0001 in the 1234 column on the bubble sheet 1 Two conducting balls hang from insulating threads as shown to the right Both balls make the same angle with respect to the vertical What definitely MUST BE TRUE about the charges on the balls A Both balls must have opposite sign charges and magnitudes must be equal B Both balls must have opposite charges C Both balls must have same sign charges and magnitudes must be equal D Both balls must have same sign charges E None of the above 2 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 simultaneously 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 The initial magnitude of the acceleration of each particle immediately after release is A kQ R2 B kQ2 R2 C kQ2 mR2 D kQ R E kQ mR2 Spring 2012 E1 4 V1 First Midterm The next two questions refer to the following situation Two negative charges are fixed on the y axis and a positive charge is fixed on the x axis as shown in the diagram The three charges form an equilateral triangle with sides of length r Point A is the origin An electron is fired from a gun to Point A along the dotted path shown Consider only electrostatic forces which act in the x y plane 0 12 3 3 When the electron is at point A in what direction is its instantaneous acceleration A B C D E The acceleration is zero so there is no direction 4 The magnitude of the force on the electron at Point A would be A kQe r cos 60o 2 B kQe cos 30o r2 C kQe r cos 30o 2 D 3kQe r2 E kQe r2 5 As shown in the figure on the left a ball of mass m with a positive charge of q hangs from a string in a uniform electric field of magnitude E The mass is at rest in a stable equilibrium What is the expression for the angle that the string makes with the vertical direction A tan 1 mg qE B tan 1 qE mg C tan 1 g E D tan 1 mg E E tan 1 E mg Spring 2012 E1 5 V1 First Midterm 6 The figure below shows the electric field for two point charges P and Q There are no other charges besides P and Q Which of the following statements about this figure are true I A positive test charge placed at the location B will experience no net force II Charges P and Q are both positive and have the same magnitude of charge III The electric field at point A is stronger than at point C since it is closer to both charges A B C D E None are true I II and III are true II III are true only II is true only III is true 7 A constant uniform horizontal electric field fills all space The Gaussian lean to surface shown consists of a vertical face A a horizontal face B a leaning face C and two side faces not labeled Face A is perpendicular to the E field The leaning face makes an angle of 30o with the horizontal C A E B E 30o How does the magnitude of the electric flux through face A A compare to the magnitude of the flux through face C c A A C B A cos 30o C C A cos 60o C D A C cos 30o Spring 2012 E A C cos 60o E1 6 V1 First Midterm 8 Two open surfaces are in an electric field caused by a positive point charge Surface A is a flat disk of radius R Surface B is a hollow hemispherical cup also of radius R Both surfaces start at the same distance from the point charge Which surface has a greater magnitude of flux through it d A Surface A B Surface B C Both are the same and are zero D Both are the same and non zero d A B 9 Two charged rods each bent in the shape of a semicircle are labeled A and B Rod A consists of a positively charged upper half with total charge Q uniformly spread along its upper half and a negatively charged lower half with total charge Q Rod B is all positively charged with total charge 2Q How do the magnitudes of the electric fields at the centers of the two rods marked with dots compare Hint Consider the E fields due to the upper and lower halves of each rod separately A EA EB both non zero B EA EB both non zero C EA EB D EA 0 EB 0 10 Two large parallel planes are shown edge on The left plane has positive charge density while the right plane has negative charge density How do the magnitudes of the electric field at points A B and C compare with each other Point A is slight closer to the left plate than Point C is A B A EA EB EC B EA EB EC C EA EB EC D EA EB EC E EA EC EB Spring 2012 E1 7 V1 First Midterm C 11 A thin uniformly charged rod has total charge Q and length L giving it a charge per unit length of Q L A point P is a distance d from the end of the rod along a line parallel to the rod What is the correct expression for the magnitude dE of electric field at point P due to the small segment dx of the rod a distance x from Point P as shown in white in the diagram 0 k dx d2 D A k dx x2 B k dx x d 2 C kQdx x2 E kQdx d2 12 A very long coaxial cable you may assume it is infinite consists of an inner cylindrical wire of radius a surrounded by a concentric outer hollow cylindrical wire of radius b If the inner wire has charge per unit length and the outer conductor has the opposite charge per unit length what the magnitude of the electric field outside the cable a distance r from the center Hint Gauss Law might be helpful here A zero B r 2 0 C r 0 D b a r 2 0 E b2 a2 r 2 0 Spring 2012 E1 8 V1 First Midterm The next two questions refer to the following situation depicted in the drawing below A small conducting …
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