Chapter 16 Electrical Energy and Capacitance CHAPTER 16 Conceptual Questions C1 Two equal positive charges are separated by d Then one of the charges is replaced by a negative charge of the same magnitude Take the potential at infinity to be zero In which situation is the potential higher midway between the charges is this value of potential zero a the first situation yes b the first situation no c the second situation yes d the second situation no C2 Case 1 An electron is released from rest in a uniform electric field Case 2 A proton is released from rest in a uniform electric field of the same magnitude as in case 1 How does the electric potential energy of the charge field system behave in these cases a In both cases the potential energy increases b In both cases the potential energy decreases c In case 1 the potential energy increases but in case 2 it decreases d In case 1 the potential energy decreases but in case 2 it increases C3 An electron and a proton are each released from rest in the same uniform electric field The electron moves a distance delectron and the proton moves a distance dproton as each particle s kinetic energy increases by 1 6 eV How do delectron and dproton compare a delectron dproton b delectron dproton c delectron dproton d The answer depends on the direction of the electric field C4 Three capacitors have capacitances C1 C2 C3 If these capacitors are connected in series which of the following is true for the resulting equivalent capacitance a Ceq C1 b Ceq C3 c Ceq C1 C2 C3 3 d None of the above is always correct C5 A capacitor is attached across a battery and charged Then the battery is removed leaving the capacitor charged The positive lead of the capacitor is then connected to one lead of a previously uncharged identical capacitor and then the other lead of the charged capacitor is connected to the other lead of the second capacitor How does the energy Eo stored in the originally charged capacitor compare to the energy Ef stored in the connected capacitors 18 Chapter 16 Electrical Energy and Capacitance a Eo Ef b Eo Ef c Eo 2Ef d Eo 4Ef 16 1 Potential Difference and Electric Potential 1 An electron charge 1 6 10 19 C moves on a path perpendicular to the direction of a uniform electric field of strength 3 0 N C How much work is done on the electron as it moves 15 cm a 4 8 10 20 J b 4 8 10 20 J c 1 6 10 20 J d zero 2 A proton 1 6 10 19 C moves 10 cm on a path in the direction of a uniform electric field of strength 3 0 N C How much work is done on the proton by the electrical field a 4 8 10 20 J b 4 8 10 20 J c 1 6 10 20 J d zero 3 A proton 1 6 10 19 C moves 10 cm along the direction of an electric field of strength 3 0 N C The electrical potential difference between the proton s initial and ending points is a 4 8 10 19 V b 0 30 V c 0 033 V d 30 V 4 A 9 0 V battery is connected between two parallel metal plates 4 0 mm apart What is the magnitude of the electric field between the plates a 2 3 103 N C b 9 0 N C c 2 3 N C d 0 75 10 6 N C 5 If an electron is accelerated from rest through a potential difference of 1 200 V find its approximate velocity at the end of this process e 1 6 10 19 C me 9 1 10 31 kg a 1 0 107 m s b 1 4 107 m s 19 Chapter 16 Electrical Energy and Capacitance c 2 1 107 m s d 2 5 107 m s 20 Chapter 16 Electrical Energy and Capacitance 6 The unit of electrical potential the volt is dimensionally equivalent to a J C b J C c C J d F C 7 The quantity of electrical potential the volt is dimensionally equivalent to a force charge b force charge c electric field distance d electric field distance 8 A free electron is in an electric field With respect to the field it experiences a force acting a parallel b anti parallel opposite in direction c perpendicular d along a constant potential line 9 A uniform electric field with a magnitude of 600 N C is directed parallel to the positive xaxis If the potential at x 3 0 m is 1 000 V what is the potential at x 1 0 m a 400 V b 1 600 V c 2 200 V d 2 500 V 10 A uniform electric field with a magnitude of 600 N C is directed parallel to the positive xaxis If the potential at x 3 0 m is 1 000 V what is the change in potential energy of a proton as it moves from x 3 0 m to x 1 0 m qp 1 6 10 19 C a 8 0 10 17 J b 1 9 10 16 J c 0 80 10 21 J d 500 J 11 An electron in a cathode ray tube is accelerated through a potential difference of 5 0 kV What kinetic energy does the electron gain in the process e 1 6 10 19 C a 1 6 10 16 J b 8 0 10 16 J 21 Chapter 16 Electrical Energy and Capacitance c 1 6 10 22 J d 8 0 1022 J 22 Chapter 16 Electrical Energy and Capacitance 12 In which case does an electric field do positive work on a charged particle a A negative charge moves opposite to the direction of the electric field b A positive charge is moved to a point of higher potential energy c A positive charge completes one circular path around a stationary positive charge d A positive charge completes one elliptical path around a stationary positive charge 13 If the distance between two isolated parallel plates that are oppositely charged is doubled the electric field between the plates is essentially unchanged However the a potential difference between the plates will double b charge on each plate will double c force on a charged particle halfway between the plates will get twice as small d force on a charged particle halfway between the plates will get four times as small 14 An electron is released from rest at the negative plate of a parallel plate capacitor If the distance across the plate is 5 0 mm and the potential difference across the plate is 5 0 V with what velocity does the electron hit the positive plate me 9 1 10 31 kg e 1 6 10 19 C a 2 6 105 m s b 5 3 106 m s c 1 0 106 m s d …