Skip to main content

Bartleby Sitemap - Textbook Solutions

All Textbook Solutions for Principles of Physics: A Calculus-Based Text

38P 39P 40P 41P 42P (a) Find the kinetic energy of the moving air in a hurricane, modeled as a disk 600 km in diameter and 11 km thick, with wind blowing at a uniform speed of 60 km/h. (b) Consider sunlight with an intensity of 1 000 W/m2 falling perpendicularly on a circular area 600 km in diameter. During what time interval would the sunlight deliver the amount of energy computed in part (a)?45P 46P 47P An idealized diesel engine operates in a cycle known as the air-standard diesel cycle shown in Figure P18.48. Fuel is sprayed into the cylinder at the point of maximum compression, B. Combustion occurs during the expansion B C, which is modeled as an isobaric process. Show that the efficiency of an engine operating in this idealized diesel cycle is e=11(TDTATCTB) Figure P18.48.49P 50P 51P 52P 53P 54P 55P 56P 57P 58P 59P 60P 61P 62P A 1.00-mol sample of an ideal monatomic gas is taken through the cycle shown in Figure P18.63. The process AB is a reversible isothermal expansion. Calculate (a) the net work done by the gas, (b) the energy added to the gas by heat, (c) the energy exhausted from the gas by heat, and (d) the efficiency of the cycle. (e) Explain how the efficiency compares with that of a Carnot engine operating between the same temperature extremes. Figure P18.63 64P 65P Three objects are brought close to one another, two at a time. When objects A and B are brought together, they repel. When objects B and C are brought together, they also repel. Which of the following statements are true? (a) Objects A and C possess charges of the same sign. (b) Objects A and C possess charges of opposite sign. (c) All three objects possess charges of the same sign. (d) One object is neutral. (e) Additional experiments must be performed to determine the signs of the charges.Three objects are brought close to one another, two at a time. When objects A and B are brought together, they attract. When objects B and C are brought together, they repel. Which of the following are necessarily true? (a) Objects A and C possess charges of the same sign. (b) Objects A and C possess charges of opposite sign. (c) All three of the objects possess charges of the same sign. (d) One object is neutral. (e) Additional experiments must be performed to determine information about the charges on the objects.Object A has a charge of +2 C, and object B has a charge of +6 C. Which statement is true about the electric forces on the objects? (a) FAB=3FBA (b)FAB=FBA (c) 3FAB=FBA (d) FAB=3FBA (e) FAB=FBA (f) 3FAB=FBA A test charge of +3 C is at a point P where an external electric field is directed to the right and has a magnitude of 4 06 N/C. If the test charge is replaced with another charge of 3 C, what happens to the external electric field at P? (a) It is unaffected. (b) It reverses direction. (c) It changes in a way that cannot be determined.Rank the magnitudes of the electric field at points A, B, and C in Figure 19.19 (greatest magnitude first). Figure 19.19 The electric field lines for two positive point charges. (The locations A, B, and C are discussed in Quick Quiz 19.5.)If the net flux through a gaussian surface is zero, the following four statements could be true. Which of the statements must be true? (a) There are no charges inside the surface. (b) The net charge inside the surface is zero. (c) The electric field is zero everywhere on the surface. (d) The number of electric field lines entering the surface equals the number leaving the surface.Consider the charge distribution shown in Active Figure 19.31. (i) What are the charges contributing to the total electric flux through surface S? (a) q1 only (b) q4 only (c) q2 and q3 (d) all four charges (e) none of the charges (ii) What are the charges contributing to the total electric field at a chosen point on the surface S? (a) q1 only (b) q4 only (c) q2 and q3 (d) all four charges (e) none of the charges Active Figure 19.31 The net electric flux through any closed surface depends only on the charge inside that surface. The net flux through surface S is ql/0, the net flux through surface S is (q2 + q3)/0, and the net flux through surface S is zero.A point charge of 4.00 nC is located at (0, 1.00) m. What is the x component of the electric field due to the point charge at (4.00, 2.00) m? (a) 1.15 N/C (b) 0.864 N/C (c) 1.44 N/C (d) 1.15 N/C (e) 0.864 N/C Charges of 3.00 nC, 2.00 nC, 7.00 nC, and 1.00 nC are contained inside a rectangular box with length 1.00 m, width 2.00 m, and height 2.50 m. Outside the box are charges of 1.00 nC and 4.00 nC. What is the electric flux through the surface of the box? (a) 0 (b) 5.64 102 N m2/C (c) 1.47 103 N m2/C (d) 1.47 103 N m2/C (e) 5.64 102 N m2/C An object with negative charge is placed in a region of space where the electric field is directed vertically upward. What is the direction of the electric force exerted on this charge? (a) It is up. (b) It is down. (c) There is no force. (d) The force can be in any direction.A particle with charge q is located inside a cubical gaussian surface. No other charges are nearby. (i) If the particle is at the center of the cube, what is the flux through each one of the faces of the cube? (a) 0 (b) q/20 (c) q/60 (d) q/80 (e) depends on the size of the cube (ii) If the particle can be moved to any point within the cube, what maximum value can the flux through one face approach? Choose from the same possibilities as in part (i).5OQ 6OQ Rank the electric fluxes through each gaussian surface shown in Figure OQ19.7 from largest to smallest. Display any cases of equality in your ranking. Figure OQ19.7 A circular ring of charge with radius b has total charge q uniformly distributed around it. What is the magnitude of the electric field at the center of the ring? (a) 0 (b) keq/b2 (c) keq2/b2 (d) keq2/b (e) none of those answers Two solid spheres, both of radius 5 cm, carry identical total charges of 2 C. Sphere A is a good conductor. Sphere B is an insulator, and its charge is distributed uniformly throughout its volume. (i) How do the magnitudes of the electric fields they separately create at a radial distance of 6 cm compare? (a) EA EB = 0 (b) EA EB 0 (c) EA = EB 0 (d) 0 EA EB (e) 0 = EA EB (ii) How do the magnitudes of the electric fields they separately create at radius 4 cm compare? Choose from the same possibilities as in part (i).An electron with a speed of 3.00 106 m/s moves into a uniform electric field of magnitude 1.00 103 N/C. The field lines are parallel to the electrons velocity and pointing in the same direction as the velocity. How far does the electron travel before it is brought to rest? (a) 2.56 cm (b) 5.12 cm (c) 11.2 cm (d) 3.34 m (e) 4.24 m A very small ball has a mass of 5.00 103 kg and a charge of 4.00 C. What magnitude electric field directed upward will balance the weight of the ball so that the ball is suspended motionless above the ground? (a) 8.21 102 N/C (b) 1.22 104 N/C (c) 2.00 102 N/C (d) 5.11 106 N/C (e) 3.72 103 N/C In which of the following contexts can Gausss law not be readily applied to find the electric field? (a) near a long, uniformly charged wire (b) above a large, uniformly charged plane (c) inside a uniformly charged ball (d) outside a uniformly charged sphere (e) Gausss law can be readily applied to find the electric field in all these contexts.Two point charges attract each other with an electric force of magnitude F. If the charge on one of the particles is reduced to one-third its original value and the distance between the particles is doubled, what is the resulting magnitude of the electric force between them? (a) 112F (b) 13F (c) 16F (d) 34F (e) 32F Three charged particles are arranged on corners of a square as shown in Figure OQ19.14, with charge Q on both the particle at the upper left corner and the particle at the lower right corner and with charge +2Q on the particle at the lower left corner. (i) What is the direction of the electric field at the upper right corner, which is a point in empty space? (a) It is upward and to the right. (b) It is straight to the right. (c) It is straight downward. (d) It is downward and to the left. (e) It is perpendicular to the plane of the picture and outward. (ii) Suppose the +2 Q charge at the lower left corner is removed. Then does the magnitude of the field at the upper right corner (a) become larger, (b) become smaller, (c) stay the same, or (d) change unpredictably? Figure OQ19.14 Assume the charged objects in Figure OQ19.15 are fixed. Notice that there is no sight line from the location of q2 to the location of q1. If you were at q1, you would be unable to see q2 because it is behind q3. How would you calculate the electric force exerted on the object with charge q1? (a) Find only the force exerted by q2 on charge q1. (b) Find only the force exerted by q3 on charge q1. (c) Add the force that q2 would exert by itself on charge q1 to the force that q3 would exert by itself on charge q1. (d) Add the force that q3 would exert by itself to a certain fraction of the force that q2 would exert by itself. (e) There is no definite way to find the force on charge q1. Figure OQ19.15 A uniform electric field exists in a region of space containing no charges. What can you conclude about the net electric flux through a gaussian surface placed in this region of space?2CQ If more electric field lines leave a gaussian surface than enter it, what can you conclude about the net charge enclosed by that surface?4CQ 5CQ 6CQ 7CQ A cubical surface surrounds a point charge q. Describe what happens to the total flux through the surface if (a) the charge is doubled, (b) the volume of the cube is doubled, (c) the surface is changed to a sphere, (d) the charge is moved to another location inside the surface, and (e) the charge is moved outside the surface.9CQ 10CQ 11CQ 12CQ 13CQ 14CQ A common demonstration involves charging a rubber balloon, which is an insulator, by rubbing it on your hair and then touching the balloon to a ceiling or wall, which is also an insulator. Because of the electrical attraction between the charged balloon and the neutral wall, the balloon sticks to the wall. Imagine now that we have two infinitely large, flat sheets of insulating material. One is charged, and the other is neutral. If these sheets are brought into contact, does an attractive force exist between them as there was for the balloon and the wall?1P (a) Calculate the number of electrons in a small, electrically neutral silver pin that has a mass of 10.0 g. Silver has 47 electrons per atom, and its molar mass is 107.87 g/mol. (b) Imagine adding electrons to the pin until the negative charge has the very large value 1.00 mC. How many electrons are added for every 109 electrons already present?Nobel laureate Richard Feynman (19181088) once said that if two persons stood at arms length from each other and each person had 1% more electrons than protons, the force of repulsion between them would be enough to lift a weight equal to that of the entire Earth. Carry out an order-of-magnitude calculation to substantiate this assertion.4P 5P 6P Two small beads having positive charges q1 = 3q and q2 = q are fixed at the opposite ends of a horizontal insulating rod of length d = 1.50 m. The bead with charge q1 is at the origin. As shown in Figure P19.7, a third small, charged bead is free to slide on the rod. (a) At what position x is the third bead in equilibrium? (b) Can the equilibrium be stable?8P Three charged particles are located at the corners of an equilateral triangle as shown in Figure P19.9. Calculate the total electric force on the 7.00-C charge.Particle A of charge 3.00 104 C is at the origin, particle B of charge 6.00 101 C is at (4.00 m, 0), and particle C of charge 1.00 104 C is at (0, 3.00 in). We wish to find the net electric force on C. (a) What is the x component of the electric force exerted by A on C? (b) What is the y component of the force exerted by A on C? (c) Kind the magnitude of the force exerted by B on C. (d) Calculate the x component of the force exerted by B on C. (e) Calculate the y component of the force exerted by B on C. (f) Sum the two x components from parts (a) and (d) to obtain the resultant x component of the electric force acting on C. (g) Similarly, find the y component of the resultant force vector acting on C. (h) Kind the magnitude and direction of the resultant electric force acting on C.11P 12P Review. A molecule of DNA (deoxyribonucleic acid) is 2.17 m long. The ends of the molecule become singly ionized: negative on one end, positive on the other. The helical molecule acts like a spring and compresses 1.00% upon becoming charged. Determine the effective spring constant of the molecule.14P 15P 16P In Figure P19.17, determine the point (other than infinity) at which the electric field is zero.18P Three point charges are arranged as shown in Figure P19.19. (a) Find the vector electric Field that the 6.00-nC and 3.00-nC charges together create at the origin. (b) Find the vector force on the 5.00-nC charge.Consider the electric dipole shown in Figure P19.20. Show that the electric field at a distant point on the + x axis is Ex 4 keqa/x3.A uniformly charged insulating rod of length 14.0 cm is bent into the shape of a semicircle as shown in Figure P 19.21. The rod has a total charge of 7.50 C. Find (a) the magnitude and (b) the direction of the electric field at O, the center of the semicircle.22P A rod 14.0 cm long is uniformly charged and has a total charge of 22.0 C. Determine (a) the magnitude and (b) the direction of the electric field along the axis of the rod at a point 36.0 cm from its center.24P 25P 26P 27P Three equal positive charges q are at the comers of an equilateral triangle of side a as shown in Figure P19.28. Assume the three charges together create an electric field. (a) Sketch the field lines in the plane of the charges. (b) Find the location of one point (other than ) where the electric field is zero. What are (c) the magnitude and (d) the direction of the electric field at P due to the two charges at the base?29P 30P 31P 32P A proton accelerates from rest in a uniform electric field of 640 N/C. At one later moment, its speed is 1.20 Mm/s (non-relativistic because v is much less than the speed of light). (a) Find the acceleration of the proton. (b) Over what time interval does the proton reach this speed? (c) How far does it move in this time interval? (d) What is its kinetic energy at the end of this interval?34P 35P 36P 37P A particle with charge Q is located a small distance immediately above the center of the flat face of a hemisphere of radius R as shown in Figure P19.38. What is the electric flux (a) through the curved surface and (b) through the flat face as 0?39P 40P A particle with charge Q = 5.00 C is located at the center of a cube of edge L = 0.100 m. In addition, six other identical charged particles having q = 1.00 C are positioned symmetrically around Q as shown in Figure P19.41. Determine the electric flux through one face of the cube.42P 43P 44P 45P A nonconducting wall carries charge with a uniform density of 8.60 C/cm2. (a) What is the electric field 7.00 cm in front of the wall if 7.00 cm is small compared with the dimensions of the wall? (b) Does your result change as the distance from the wall varies? Explain.In nuclear fission, a nucleus of uranium-238, which contains 92 protons, can divide into two smaller spheres, each having 46 protons and a radius of 5.90 1015 m. What is the magnitude of the repulsive electric force pushing the two spheres apart?Consider a long, cylindrical charge distribution of radius R with a uniform charge density . Find the electric field at distance r from the axis, where r R.A 10.0-g piece of Styrofoam carries a net charge of 0.700 C and is suspended in equilibrium above the center of a large, horizontal sheet of plastic that has a uniform charge density on its surface. What is the charge per unit area on the plastic sheet?An insulating solid sphere of radius a has a uniform volume charge density and carries a total positive charge Q. A spherical gaussian surface of radius r, which shares a common center with the insulating sphere, is inflated starting from r = 0. (a) Find an expression for the electric flux passing through the surface of the gaussian sphere as a function of r for r a. (b) Find an expression for the electric flux for r a. (c) Plot the flux versus r.A large, flat, horizontal sheet of charge has a charge per unit area of 9.00 C/m2. Find the electric field just above the middle of the sheet.A cylindrical shell of radius 7.00 cm and length 2.40 m has its charge uniformly distributed on its curved surface. The magnitude of the electric field at a point 19.0 cm radially outward from its axis (measured from the midpoint of the shell) is 36.0 kN/C. Find (a) the net charge on the shell and (b) the electric field at a point 4.00 cm from the axis, measured radially outward from the midpoint of the shell.Consider a thin, spherical shell of radius 14.0 cm with a total charge of 32.0 C distributed uniformly on its surface. Find the electric field (a) 10.0 cm and (b) 20.0 cm from the center of the charge distribution.54P 55P 56P A solid conducting sphere of radius 2.00 cm has a charge 8.00 μC. A conducting spherical shell of inner radius 4.00 cm and outer radius 5.00 cm is concentric with the solid sphere and has a total charge −4.00 μC. Find the electric field at (a) r = 1.00 cm, (b) r = 3.00 cm, (c) r = 4.50 cm, and (d) r = 7.00 cm from the center of this charge configuration. A very large, thin, flat plate of aluminum of area A has a total charge Q uniformly distributed over its surfaces. Assuming the same charge is spread uniformly over the upper surface of an otherwise identical glass plate, compare the electric fields just above the center of the upper surface of each plate.A thin, square, conducting plate 50.0 cm on a side lies in the xy plane. A total charge of 4.00 108 C is placed on the plate. Find (a) the charge density on each face of the plate, (b) the electric field just above the plate, and (c) the electric field just below the plate. You may assume the charge density is uniform.A long, straight wire is surrounded by a hollow metal cylinder whose axis coincides with that of the wire. The wire has a charge per unit length of , and the cylinder has a net charge per unit length of 2. From this information, use Gausss law to find (a) the charge per unit length on the inner surface of the cylinder, (b) the charge per unit length on the outer surface of the cylinder, and (c) the electric field outside the cylinder a distance r from the axis.A square plate of copper with 50.0-cm sides has no net charge and is placed in a region of uniform electric field of 80.0 kN/C directed perpendicularly to the plate. Find (a) the charge density of each face of the plate and (b) the total charge on each face.62P 63P 64P 65P Why is the following situation impossible? An electron enters a region of uniform electric field between two parallel plates. The plates are used in a cathode-ray tube to adjust the position of an electron beam on a distant fluorescent screen. The magnitude of the electric field between the plates is 200 N/C. The plates are 0.200 m in length and are separated by 1.50 cm. The electron enters the region at a speed of 3.00 106 m/s, traveling parallel to the plane of the plates in the direction of their length. It leaves the plates heading toward its correct location on the fluorescent screen.A small, 2.00-g plastic ball is suspended by a 20.0-cm-long string in a uniform electric field as shown in Figure P19.67. If the hall is in equilibrium when the string makes a 15.0 angle with the vertical, what is the net charge on the ball?Two point charges qA = 12.0 C and qB = 45.0 C and a third particle with unknown charge qC are located on the x axis. The particle qA is at the origin, and qB is at x = 15.0 cm. The third particle is to be placed so that each particle is in equilibrium under the action of the electric forces exerted by the other two particles. (a) Is this situation possible? If so, is it possible in more than one way? Explain. Find (b) the required location and (c) the magnitude and the sign of the charge of the third particle.69P 70P 71P Two small spheres of mass m are suspended from strings of length that are connected at a common point. One sphere has charge Q and the other charge 2Q. The strings make angles 1 and 2 with the vertical. (a) Explain how 1, and 2 are related. (b) Assume 1 and 2 are small. Show that the distance r between the spheres is approximately r=(4keQ2mg)1/3 Two infinite, nonconducting sheets of charge are parallel to each other as shown in Figure P19.73. The sheet on the left has a uniform surface charge density , and the one on the right hits a uniform charge density . Calculate the electric field at points (a) to the left of, (b) in between, and (c) to the right of the two sheets. (d) What If? Find the electric fields in all three regions if both sheets have positive uniform surface charge densities of value .Consider the charge distribution shown in Figure P19.74. (a) Show that the magnitude of the electric field at the center of any face of the cube has a value of 2.18 keq/s2. (b) What is the direction of the electric field at the center of the top face of the cube?A solid, insulating sphere of radius a has a uniform charge density throughout its volume and a total charge Q. Concentric with this sphere is an uncharged, conducting, hollow sphere whose inner and outer radii are b and c as shown in Figure P19.75. We wish to understand completely the charges and electric fields at all locations. (a) Find the charge contained within a sphere of radius r a. (b) From this value, find the magnitude of the electric field for r a. (c) What charge is contained within a sphere of radius r when a r b? (d) From this value, find the magnitude of the electric field for r when a r b. (e) Now consider r when b r c. What is the magnitude of the electric field for this range of values of r? (f) From this value, what must be the charge on the inner surface of the hollow sphere? (g) From part (f), what must be the charge on the outer surface of the hollow sphere? (h) Consider the three spherical surfaces of radii a, b, and c. Which of these surfaces has the largest magnitude of surface charge density?76P 77P 78P In Figure 20. 1, two points and are located within a region in which there is an electric field. (i) How would you describe the potential difference V = V V? (a) It is positive. (b) It is negative. (c) It is zero. (ii) A negative charge is placed at and then moved to . How would you describe the change in potential energy of the chargefield system for this process? Choose from the same possibilities. Figure 20.1 (Quick Quiz 20.1) Two points in an electric field.The labeled points in Figure 20.4 are on a series of equipotential surfaces associated with an electric field. Rank (from greatest to least) the work done by the electric field on a positively charged particle that moves from to , from to , from to , and from to . Figure 20.4 (Quick Quiz 20.2) Four equipotential surfaces.A spherical balloon contains a positively charged object at its center. (i) As the balloon is inflated to a greater volume while the charged object remains at the center, does the electric potential at the surface of the balloon (a) increase, (b) decrease, or (c) remain the same? (ii) Does the electric flux through the surface of the balloon (a) increase, (b) decrease, or (c) remain the same?In Active Figure 20.8a, take q1 to be a negative source charge and q2 to be the test charge. (i) If q2 is initially positive and is changed to a charge of the same magnitude but negative, what happens to the potential at the position of q2 due to q1? (a) It increases. (b) It decreases. (c) It remains the same. (ii) When q2 is changed from positive to negative, what happens to the potential energy of the two-charge system? Choose from the same possibilities.In a certain region of space, the electric potential is zero everywhere along the x axis. (i) From this information, you can conclude that the x component of the electric field in this region is (a) zero, (b) in the positive x direction, or (c) in the negative x direction. (ii) Suppose the electric potential is +2 V everywhere along the x axis. From the same choices, what can you conclude about the x component of the electric field now?A capacitor stores charge Q at a potential difference V. What happens if the voltage applied to a capacitor by a battery is doubled to 2 V? (a) The capacitance falls to half its initial value, and the charge remains the same. (b) The capacitance and the charge both fall to half their initial values. (c) The capacitance and the charge both double. (d) The capacitance remains the same, and the charge doubles.20.7QQ 20.8QQ If you have ever tried to hang a picture or a mirror, you know it can be difficult to locate a wooden stud in which to anchor your nail or screw. A carpenters stud finder is a capacitor with its plates arranged side by side instead of facing each other as shown in Figure 20.32. When the device is moved over a stud, does the capacitance (a) increase or (b) decrease?A parallel-plate capacitor is charged and then is disconnected from the battery. By what factor does the stored energy change when the plate separation is then doubled? (a) It becomes four times larger. (b) It becomes two times larger. (c) It stays the same. (d) It becomes one-half as large. (e) It becomes one-fourth as large.2OQ A proton is released from rest at the origin in a uniform electric field in the positive x direction with magnitude 850 N/C. What is the change in the electric potential energy of the protonfield system when the proton travels to x = 2.50 m? (a) 3.40 1016 J (b) 3.40 1016 J (c) 2.50 1016 J (d) 2.50 1016 J (e) 1.60 1019 J By what factor is the capacitance of a metal sphere multiplied if its volume is tripled? (a) 3 (b) 31/3 (c) 1 (d) 31/3 (e) 13 5OQ Rank the potential energies of the four systems of particles shown in Figure OQ20.6 from largest to smallest. Include equalities if appropriate. Figure OQ20.6 7OQ In a certain region of space, a uniform electric field is in the x direction. A particle with negative charge is carried from x = 20.0 cm to x = 60.0 cm. (i) Does the electric potential energy of the charge-field system (a) increase, (b) remain constant, (c) decrease, or (d) change unpredictably? (ii) Has the particle moved to a position where the electric potential is (a) higher than before, (b) unchanged, (c) lower than before, or (d) unpredictable?9OQ 10OQ 11OQ A parallel-plate capacitor is connected to a battery. What happens to the stored energy if the plate separation is doubled while the capacitor remains connected to the battery? (a) It remains the same. (b) It is doubled. (c) It decreases by a factor of 2. (d) It decreases by a factor of 4. (e) It increases by a factor of 4.Rank the electric potential energies of the systems of charges shown in Figure OQ20.13 from largest to smallest. Indicate equalities if appropriate. Figure OQ20.13 Four particles are positioned on the rim of a circle. The charges on the particles are +0.500 C, +1.50 C, 1.00 C, and 0.500 C. If the electric potential at the center of the circle due to the +0.500 C charge alone is 4.50 104 V, what is the total electric potential at the center due to the four charges? (a) 18.0 104 V (b) 4.50 104 V (c) 0 (d) 4.50 104 V (e) 9.00 104 V 15OQ A filament running along the x axis from the origin to x = 80.0 cm carries electric charge with uniform density. At the point P with coordinates (x = 80.0 cm, y = 80.0 cm), this filament creates electric potential 100 V. Now we add another filament along the y axis, running from the origin to y = 80.0 cm, carrying the same amount of charge with the same uniform density. At the same point P, is the electric potential created by the pair of filaments (a) greater than 200 V, (b) 200 V, (c) 100 V, (d) between 0 and 200 V, or (e) 0?An electronics technician wishes to construct a parallel plate capacitor using rutile ( = 100) as the dielectric. The area of the plates is 1.00 cm2. What is the capacitance if the rutile thickness is 1.00 mm? (a) 88.5 pF (b) 177 pF (c) 8.85 F (d) 100 F (e) 35.4 F 18OQ 19OQ A parallel-plate capacitor filled with air carries a charge Q. The battery is disconnected, and a slab of material with dielectric constant = 2 is inserted between the plates. Which of the following statements is true? (a) The voltage across the capacitor decreases by a factor of 2. (b) The voltage across the capacitor is doubled. (c) The charge on the plates is doubled. (d) The charge on the plates decreases by a factor of 2. (e) The electric field is doubled.21OQ 1CQ 2CQ 3CQ 4CQ 5CQ 6CQ 7CQ 8CQ Why is it dangerous to touch the terminals of a high-voltage capacitor even after the voltage source that charged the capacitor is disconnected from the capacitor? (b) What can be done to make the capacitor safe to handle after the voltage source has been removed?10CQ 11CQ 12CQ A uniform electric field of magnitude 325 V/m is directed in the negative y direction in Figure P20.1. The coordinates of point are (0.200, 0.300) m, and those of point are (0.400, 0.500) m. Calculate the electric potential difference using the dashed-line path. Figure P20.1 2P Calculate the speed of a proton that is accelerated from rest through an electric potential difference of 120 V. Calculate the speed of an electron that is accelerated through the same electric potential difference.4P An electron moving parallel to the x axis has an initial speed of 3.70 106 m/s at the origin. Its speed is reduced to 1.40 105 m/s at the point x = 2.00 cm. (a) Calculate the electric potential difference between the origin and that point. (b) Which point is at the higher potential?(a) Find the potential at a distance of 1.00 cm from a proton. (b) What is the potential difference between two points that are 1.00 cm and 2.00 cm from a proton? (c) Repeat parts (a) and (b) for an electron.8P Given two particles with 2.00-C charges as shown in Figure P20.9 and a particle with charge q = 1.28 1018 C at the origin, (a) what is the net force exerted by the two 2.00-C charges on the test charge q? (b) What is the electric field at the origin due to the two 2.00-C particles? (c) What is the electric potential at the origin due to the two 2.00-C particles? Figure P20.9 Three particles with equal positive charges q are at the corners of an equilateral triangle of side a as shown in Figure P20.10. (a) At what point, if any, in the plane of the particles is the electric potential zero? (b) What is the electric potential at the position of one of the particles due to the other two particles in the triangle? Figure P20.10 The three charged particles in Figure P20.11 are at the vertices of an isosceles triangle (where d = 2.00 cm). Taking q = 7.00 C, calculate the electric potential at point A, the midpoint of the base. Figure P20.11 12P 13P Review. A light, unstressed spring has length d. Two identical particles, each with charge q, are connected to the opposite ends of the spring. The particles are held stationary a distance d apart and then released at the same moment. The system then oscillates on a frictionless, horizontal table. The spring has a bit of internal kinetic friction, so the oscillation is damped. The particles eventually stop vibrating when the distance between them is 3d. Assume the system of the spring and two charged particles is isolated. Find the increase in internal energy that appears in the spring during the oscillations.Review. Two insulating spheres have radii 0.300 cm and 0.500 cm, masses 0.100 kg and 0.700 kg, and uniformly distributed charges 2.00 C and 3.00 C. They are released from rest when their centers are separated by 1.00 m. (a) How fast will each be moving when they collide? (b) What If? If the spheres were conductors, would the speeds be greater or less than those calculated in part (a)? Explain.Review. Two insulating spheres have radii r1 and r2, masses m1 and m2, and uniformly distributed charges q1 and q2. They are released from rest when their centers are separated by a distance d. (a) How fast is each moving when they collide? (b) What If? If the spheres were conductors, would their speeds be greater or less than those calculated in part (a)? Explain.Two particles each with charge +2.00 C are located on the x axis. One is at x = 1.00 m, and the other is at x = 1.00 m. (a) Determine the electric potential on the y axis at y = 0.500 m. (b) Calculate the change in electric potential energy of the system as a third charged particle of 3.00 C is brought from infinitely far away to a position on the y axis at y = 0.500 m.18P Two particles, with charges of 20.0 nC and 20.0 nC, are placed at the points with coordinates (0, 4.00 cm) and (0, 4.00 cm) as shown in Figure P20.19. A particle with charge 10.0 nC is located at the origin. (a) Find the electric potential energy of the configuration of the three fixed charges. (b) A fourth particle, with a mass of 2.00 1013 kg and a charge of 40.0 nC, is released from rest at the point (3.00 cm, 0). Find its speed after it has moved freely to a very large distance away.At a certain distance from a charged particle, the magnitude of the electric field is 500 V/m and the electric potential is 3.00 kV. (a) What is the distance to the particle? (b) What is the magnitude of the charge?A particle with charge +q is at the origin. A particle with charge 2q is at x = 2.00 m on the x axis. (a) For what finite value(s) of x is the electric field zero? (b) For what finite value(s) of x is the electric potential zero?22P 23P 24P 25P A rod of length L (Fig. P20.26) lies along the x axis with its left end at the origin. It has a nonuniform charge density = x, where is a positive constant. (a) What are the units of ? (b) Calculate the electric potential at A. Figure P20.26 For the arrangement described in Problem 26, calculate the electric potential at point B, which lies on the perpendicular bisector of the rod a distance b above the x axis. Figure P20.26 A wire having a uniform linear charge density is bent into the shape shown in Figure P20.28. Find the electric potential at point O. Figure P20.28 A uniformly charged insulating rod of length 14.0 cm is bent into the shape of a semicircle as shown in Figure P20.29. The rod has a total charge of 7.50 C. Find the electric potential at O, the center of the semicircle. Figure P20.29 How many electrons should be removed from an initially uncharged spherical conductor of radius 0.300 m to produce a potential of 7.50 kV at the surface?31P 32P (a) How much charge is on each plate of a 4.00-F capacitor when it is connected to a 12.0-V battery? (b) If this same capacitor is connected to a 1.50-V battery, what charge is stored?Two conductors having net charges of +10.0 C and 10.0 C have a potential difference of 10.0 V between them. (a) Determine the capacitance of the system. (b) What is the potential difference between the two conductors if the charges on each are increased to +100 C and 100 C?35P A spherical capacitor consists of a spherical conducting shell of radius b and charge 2Q that is concentric with a smaller conducting sphere of radius a and charge +Q (Fig. P20.36). (a) Show that its capacitance is C=abke(ba) (b) Show that as b approaches infinity, the capacitance approaches the value a/ke = 40a. Figure P20.36 37P A variable air capacitor used in a radio tuning circuit is made of N semicircular plates, each of radius R and positioned a distance d from its neighbors, to which it is electrically connected. As shown in Figure P20.38, a second identical set of plates is enmeshed with the first set. Each plate in the second set is halfway between two plates of the first set. The second set can rotate as a unit. Determine the capacitance as a function of the angle of rotation , where = 0 corresponds to the maximum capacitance. Figure P20.38 39P 40P (a) Regarding the Earth and a cloud layer 800 m above the Earth as the plates of a capacitor, calculate the capacitance of the Earthcloud layer system. Assume the cloud layer has an area of 1.00 km2 and the air between the cloud and the ground is pure and dry. Assume charge builds up on the cloud and on the ground until a uniform electric field of 3.00 106 N/C throughout the space between them makes the air break down and conduct electricity as a lightning bolt. (b) What is the maximum charge the cloud can hold?42P 43P (a) Find the equivalent capacitance between points a and b for the group of capacitors connected as shown in Figure P20.44. Take C1 = 5.00 F, C2 = 10.0 F, and C3 = 2.00 F. (b) What charge is stored on C3 if the potential difference between points a and b is 60.0 V? Figure P20.44 Four capacitors are connected as shown in Figure P20.45. (a) Find the equivalent capacitance between points a and b. (b) Calculate the charge on each capacitor, taking Vab = 15.0 V. Figure P20.45 46P According to its design specification, the timer circuit delaying the closing of an elevator door is to have a capacitance of 32.0 F between two points A and B. When one circuit is being constructed, the inexpensive but durable capacitor installed between these two points is found to have capacitance 34.8 F. To meet the specification, one additional capacitor can be placed between the two points. (a) Should it be in series or in parallel with the 34.8-F capacitor? (b) What should be its capacitance? (c) What If? The next circuit comes down the assembly line with capacitance 29.8 F between A and B. To meet the specification, what additional capacitor should be installed in series or in parallel in that circuit?48P 49P Three capacitors are connected to a battery as shown in Figure P20.50. Their capacitances are C1 = 3C, C2 = C, and C3 = 5C. (a) What is the equivalent capacitance of this set of capacitors? (b) State the ranking of the capacitors according to the charge they store from largest to smallest. (c) Rank the capacitors according to the potential differences across them from largest to smallest. (d) What If? Assume C3 is increased. Explain what happens to the charge stored by each capacitor. Figure P20.50 Find the equivalent capacitance between points a and b in the combination of capacitors shown in Figure P20.51. Figure P20.51 Consider the circuit shown in Figure P20.52, where C1 = 6.00 F, C2 = 3.00 F, and V = 20.0 V. Capacitor C1 is first charged by closing switch S1. Switch S1 is then opened, and the charged capacitor is connected to the uncharged capacitor by closing S2. Calculate (a) the initial charge acquired by C1 and (b) the final charge on each capacitor. Figure P20.52 53P A parallel-plate capacitor has a charge Q and plates of area A. What force acts on one plate to attract it toward the other plate? Because the electric field between the plates is E = Q/A0, you might think the force is F = QE = Q2/A0. This conclusion is wrong because the field E includes contributions from both plates, and the field created by the positive plate cannot exert any force on the positive plate. Show that the force exerted on each plate is actually F = Q2/2A0. Suggestion: Let C = 0A/x for an arbitrary plate separation x and note that the work done in separating the two charged plates is W=Fdx.55P 56P 57P 58P 59P 60P A uniform electric field E = 3 000 V/m exists within a certain region. What volume of space contains an energy equal to 1.00 107 J? Express your answer in cubic meters and in liters.62P 63P 64P 65P A parallel-plate capacitor in air has a plate separation of 1.50 cm and a plate area of 25.0 cm2. The plates are charged to a potential difference of 250 V and disconnected from the source. The capacitor is then immersed in distilled water. Assume the liquid is an insulator. Determine (a) the charge on the plates before and after immersion, (b) the capacitance and potential difference after immersion, and (c) the change in energy of the capacitor.Lightning can be studied with a Van de Graaff generator, which consists of a spherical dome on which charge is continuously deposited by a moving belt. Charge can be added until the electric field at the surface of the dome becomes equal to the dielectric strength of air. Any more charge leaks off in sparks as shown in Figure P20.67. Assume the dome has a diameter of 30.0 cm and is surrounded by dry air with a breakdown electric field of 3.00 106 V/m. (a) What is the maximum potential of the dome? (b) What is the maximum charge on the dome? Figure P20.67 David Evison/Shutterstock.com 68P 69P 70P 71P 72P 73P 74P 75P 76P 77P 78P 79P 80P 81P 82P A 10.0-F capacitor is charged to 15.0 V. It is next connected in series with an uncharged 5.00-F capacitor. The series combination is finally connected across a 50.0-V battery as diagrammed in Figure P20.83. Find the new potential differences across the 5.00-F and 10.0-F capacitors after the switch is thrown closed. Figure P20.83 Two large, parallel metal plates, each of area A, are oriented horizontally and separated by a distance 3d. A grounded conducting wire joins them, and initially each plate carries no charge. Now a third identical plate carrying charge Q is inserted between the two plates, parallel to them and located a distance d from the upper plate as shown in Figure P20.84. (a) What induced charge appears on each of the two original plates? (b) What potential difference appears between the middle plate and each of the other plates? Figure P20.84 A capacitor is constructed from two square, metallic plates of sides and separation d. Charges +Q and Q are placed on the plates, and the power supply is then removed. A material of dielectric constant K is inserted a distance x into the capacitor as shown in Figure P20.85. Assume d is much smaller than x. (a) Find the equivalent capacitance of the device. (b) Calculate the energy stored in the capacitor. (c) Find the direction and magnitude of the force exerted by the plates on the dielectric. (d) Obtain a numerical value for the force when x = /2, assuming = 5.00 cm, d = 2.00 mm, the dielectric is glass ( = 4.50), and the capacitor was charged to 2.00 103 V before the dielectric was inserted. Suggestion: The system can be considered as two capacitors connected in parallel. Figure P20.85 Two square plates of sides are placed parallel to each other with separation d as suggested in Figure P20.86. You may assume d is much less than . The plates carry uniformly distributed static charges +Q0 and Q0. A block of metal has width , length , and thickness slightly less than d. It is inserted a distance x into the space between the plates. The charges on the plates remain uniformly distributed as the block slides in. In a static situation, a metal prevents an electric field from penetrating inside it. The metal can be thought of as a perfect dielectric, with . (a) Calculate the stored energy in the system as a function of x. (b) Find the direction and magnitude of the force that acts on the metallic block. (c) The area of the advancing front face of the block is essentially equal to d. Considering the force on the block as acting on this face, find the stress (force per area) on it. (d) Express the energy density in the electric field between the charged plates in terms of Q0, , d, and 0. (e) Explain how the answers to parts (c) and (d) compare with each other. Figure P20.86 Determine the equivalent capacitance of the combination shown in Figure P20.87. Suggestion: Consider the symmetry involved. Figure P20.87 Consider positive and negative charges moving horizontally through the four regions shown in Figure 21.3. Rank the currents in these four regions, from highest to lowest.21.2QQ When does an incandescent lightbulb carry more current? (a) immediately after it is turned on and the glow of the metal filament is increasing or (b) after it has been on for a few milliseconds and the glow is steady?For the two incandescent lightbulbs shown in Figure 21.12, rank the currents at points a through f, from greatest to least.21.5QQ With the switch in the circuit of Figure 21.18a open, there is no current in R2. There is current in R1, however, and it is measured with the ammeter at the right side of the circuit. If the switch is closed (Fig. 21.18b), there is current in R2. What happens to the reading on the ammeter when the switch is closed? (a) The reading increases. (b) The reading decreases. (c) The reading does not change.21.7QQ Consider the circuit in Figure 21.29 and assume the batter has no internal resistance. (i) Just after the switch is closed, what is the current in the battery? (a) 0 (b) /2R (c) 2/R (d) /R (e) impossible to determine (ii) After a very long time, what is the current in the battery? Choose from the same choices.If the terminals of a battery with zero internal resistance are connected across two identical resistors in series, the total power delivered by the battery is 8.00 W. If the same battery is connected across the same resistors in parallel, what is the total power delivered by the battery? (a) 16.0 W (b) 32.0 W (c) 2.00 W (d) 4.00 W (e) none of those answers Wire B has twice the length and twice the radius of wire A. Both wires are made from the same material. If wire A has a resistance R, what is the resistance of wire B? (a) 4R (b) 2R (c) R (d) 12R (e) 14R The current-versus-voltage behavior of a certain electrical device is shown in Figure OQ21.3. When the potential difference across the device is 2 V, what is its resistance? (a) 1 (b) 34 (c) 43 (d) undefined (e) none of those answers 4OQ A potential difference of 1.00 V is maintained across a 10.0- resistor for a period of 20.0 s. What total charge passes by a point in one of the wires connected to the resistor in this time interval? (a) 200 C (b) 20.0 C (c) 2.00 C (d) 0.005 00 C (e) 0.050 0 C 6OQ A metal wire of resistance R is cut into three equal pieces that are then placed together side by side to form a new cable with a length equal to one-third the original length. What is the resistance of this new cable? (a) 19R (b) 13R (c) R (d) 3R (e) 9R The terminals of a battery are connected across two resistors in parallel. The resistances of the resistors are not the same. Which of the following statements is correct? Choose all that are correct. (a) The resistor with the larger resistance carries more current than the other resistor. (b) The resistor with the larger resistance carries less current than the other resistor. (c) The potential difference across each resistor is the same. (d) The potential difference across the larger resistor is greater than the potential difference across the smaller resistor. (e) The potential difference is greater across the resistor closer to the battery.9OQ Two conducting wires A and B of the same length and radius are connected across the same potential difference. Conductor A has twice the resistivity of conductor B. What is the ratio of the power delivered to A to the power delivered to B? (a) 2 (b) 2 (c) 1 (d) 1/2 (e) 12 When resistors with different resistances are connected in series, which of the following must be the same for each resistor? Choose all correct answers. (a) potential difference (b) current (c) power delivered (d) charge entering each resistor in a given time interval (e) none of those answers When operating on a 120-V circuit, an electric heater receives 1.30 103 W of power, a toaster receives 1.00 103 W, and an electric oven receives 1.54 103 W. If all three appliances are connected in parallel on a 120-V circuit and turned on, what is the total current drawn from an external source? (a) 24.0 A (b) 32.0 A (c) 40.0 A (d) 48.0 A (e) none of those answers 13OQ 14OQ In the circuit shown in Figure OQ21.15, each battery is delivering energy to the circuit by electrical transmission. All the resistors have equal resistance. (i) Rank the electric potentials at points a, b, c, d, and e from highest to lowest, noting any cases of equality in the ranking. (ii) Rank the magnitudes of the currents at the same points from greatest to least, noting any cases of equality.1CQ 2CQ 3CQ Referring to Figure CQ21.4, describe what happens to the light-bulb after the switch is closed. Assume the capacitor has a large capacitance and is initially uncharged. Also assume the light illuminates when connected directly across the battery terminals.When the potential difference across a certain conductor is doubled, the current is observed to increase by a factor of 3. What can you conclude about the conductor?Use the atomic theory of matter to explain why the resistance of a material should increase as its temperature increases.7CQ

Page: [1][2][3][4][5][6][7][8][9][10][11]