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physics
college physics a strategic approach 2nd
College Physics Essentials Electricity And Magnetism Optics Modern Physics Volume Two 8th Edition Jerry D. Wilson, Anthony J. Buffa, Bo Lou - Solutions
15. In the previous question, what is the field direction at the location y = +40 cm, x = 0 cm: (a) right, (b) left,(c) up, or (d) down?
16. In electrostatic equilibrium, is the electric field just below the surface of a charged sphere of radius R(a) the same value as the field just above the surface,(b) zero, (c) dependent on the amount of charge on the conductor, or (d) given by kq/R2?
11. A small charged object is placed and held just above the positive end of an electric dipole. The dipole starts to accelerate downward when released. (a) What is the sign of the charge on the object? (b) What would happen to the dipole if released when same charged object was held just below the
10. Two point charges are initially separated by a distanced. Suppose the charge of one is increased by twentyseven times while the charge of the other is reduced to one-third its initial value. What would their separation distance have to be, expressed in terms ofd, so as to keep the force between
8. Two point charges initially exert an electric force of magnitude F on one another. Suppose the charge of one was halved and that of the other was quadrupled.Write the new force be in terms of F and explain your reasoning.
7. Suppose the negatively charged balloon in Figure 15.6c was replaced by a positively charged glass rod.Which way would the water stream bend now, if at all?Explain your reasoning.
5. Is there an overall gain or loss of electrons by an object when it is electrically polarized? Explain.
3. If a neutral piece of metal becomes negatively charged, does its mass increase or decrease? What if it becomes positively charged?
2. An electrically neutral object can be given a net charge by several means. Does this violate the law of conservation of charge? Explain.
1. If the charge on the electron were designated as positive and that of the proton negative, what do you think would be the overall effect on the physical universe as we know it?
18. The direction of the electric field at the surface of a charged conductor under electrostatic conditions(a) is parallel to the surface, (b) is perpendicular to the surface, (c) is at a 45° angle to the surface, or(d) depends on the charge on the conductor.
17. An uncharged thin metal slab is oriented perpendicularly to an external electric field that points horizontally to the left. What is the direction of the electric field inside the slab? (a) left, (b) right, or (c) it has none because it is zero.
1. A combination of two electrons and three protons would have a net charge of (a) +1, (b) − 1, (c) +1.6×10−19C,(d) −1.6×10−19C.
3. Using the language of electrical potential and energy(not forces), explain why positive charges speed up when they are released near negative charges.
12. A proton with an initial kinetic energy of 9.50 eV is fired directly at another proton whose location is fixed. When the moving proton has reached its point of closest approach, by how much has the electric potential energy of this two-particle system changed:(a) +9.50 eV, (b) −9.50 eV, (c)
11. As an electron is moved perpendicularly away from a large uniformly charged plate, the system’s electrostatic potential energy is observed to decrease. The charge on the plate must be (a) positive, (b) negative, (c) zero.
10. An electron is moved from an equipotential surface at +5.0 V to one at +10.0 V. It is moving generally in a direction (a) parallel to the electric field, (b) opposite to the electric field, (c) you can’t tell its direction relative to the electric field from the data given.
9. Equipotential surfaces (a) are parallel to the electric field, (b) are perpendicular to the electric field, (c) can be at any angle with respect to the electric field.
8. On an equipotential surface (a) the electric potential is constant, (b) the electric field is zero, (c) the electric potential is zero, (d) there are equal negative and positive charges.
7. The charge on each of two closely spaced oppositely charged parallel plates is increased equally. What happens to the potential difference between them:(a) it increases, (b) it decreases, (c) it stays the same, or(d) you can’t tell from the information given?
6. The spacing between two closely spaced oppositely charged parallel plates is decreased. What happens to the potential difference between them, assuming they are isolated: (a) it increases, (b) it decreases, (c) it stays the same, or (d) you can’t tell from the data given?
5. A positive point charge is fixed at the origin, and an electron is brought near to it from a large distance. If the magnitude of the work to move the electron is called W, then the change in the system’s potential energy is(a) +W, (b) −W, (c) zero, (d) unrelated to W.
4. An isolated system consists of three point charges.Two are negative and one is positive. What can you say about the sign of this system’s potential energy: (a) it is positive, (b) it is negative, (c) it is zero, or (d) you can’t tell from the data given?
3. An electron is moved from the positive plate to the negative plate of a charged parallel plate arrangement.How does the sign of the change in the system’s electrostatic potential energy compare to the sign of the change in electrostatic potential the electron experiences:(a) both are positive,
2. How does the electrostatic potential energy of a system of two positive point charges change when the distance between them is tripled: (a) it is reduced to one-third its original value, (b) it is reduced to one-ninth its original value, (c) it is unchanged, or(d) it is increased to three times
1. The SI unit of electric potential difference is the(a) joule, (b) newton per coulomb, (c) newton-meter,(d) joule per coulomb.
50. ••• A proton is fired into a uniform electric field, opposite to the direction of the field. The proton’s speed upon entering the field is 3.15 × 105 m/s, and it comes to rest 5.25 cm after entering the field.(a) What is the electric field strength? (b) What is the proton’s velocity
13. A capacitor is first connected to a 6.0-V battery and then disconnected and connected to a 12.0-V battery.How does its capacitance change: (a) it increases,(b) it decreases, (c) it stays the same?
14. A capacitor is first connected to a 6.0-V battery and then disconnected and connected to a 12.0-V battery.How does the charge on either of its plates change:(a) it increases, (b) it decreases, (c) it stays the same?
1. What is the difference between (a) electrostatic potential energy and electric potential and (b) electric potential difference and voltage?
25. Capacitors 1, 2, and 3 all have the same capacitance, C.1 and 2 are in series and that combination is in parallel with 3. What is the total capacitance of this system:(a) C, (b) 1.5C, (c) 3C, or (d) C/3?
24. Capacitors in parallel must have the same (a) voltage,(b) charge, (c) energy storage, (d) none of these.
23. Capacitors in series must have the same (a) voltage,(b) charge, (c) energy storage, (d) none of these.
22. A parallel plate capacitor is first connected to a battery for a while and then disconnected from it. If a dielectric is now inserted between the plates, what happens to the electric field there: (a) it decreases,(b) it increases, (c) it remains the same, (d) the field may increase, decrease,
21. A parallel plate capacitor is connected to a battery and remains so. If a dielectric is now inserted between the plates, what happens to the electric field there:(a) it decreases, (b) it increases, (c) it remains the same,(d) it may increase, decrease, or not change depending on the dielectric
20. A parallel plate capacitor is connected to a battery for a while and then disconnected from it. If a dielectric is then inserted between the plates, what happens to the charge on its plates: (a) the charge decreases,(b) the charge increases, or (c) the charge stays the same?
19. A parallel plate capacitor is connected to a battery and remains so. If a dielectric is then inserted between the plates, (a) the capacitance decreases, (b) the voltage increases, (c) the voltage decreases, (d) the charge increases.
18. Putting a dielectric into a charged parallel plate capacitor that is not connected to a battery (a) decreases the capacitance, (b) decreases the voltage, (c) increases the charge, (d) causes the plates to discharge because the dielectric is a conductor.
17. The area of the plates of a capacitor is reduced. How should the distance between those plates be adjusted to keep the capacitance constant: (a) increase it,(b) decrease it, or (c) changing the distance cannot make up for the plate area change?
16. The distance between the plates of a capacitor is cut in half. By what factor does its capacitance change:(a) it is cut in half, (b) it is reduced to one-fourth its original value, (c) it is doubled, or (d) it is quadrupled?
15. A capacitor is first connected to a 6.0-V battery and then disconnected and connected to a 12.0-V battery. By how much does the electric field strength between its plates change: (a) it is two times greater,(b) it is four times greater, or (c) it stays the same?
32. •• Compute the electric field at a point midway between charges q1 and q2 in Figure 15.21.
31. •• What is the electric field at the center of the triangle in Figure 15.21?
30. •• Two charges of +4.0 μC and +9.0 μC are 30 cm apart. Where on the line joining the charges is the electric field zero?
25. • At what distance from a proton is the magnitude of its electric field 1.0 × 105 N/C?
24. • What are the magnitude and direction of the electric field at a point 0.75 cm away from a point charge of+2.0 pC?
23. • An electron is acted on by two electric forces, one of 2.7 × 10−14 N acting upward and a second of 3.8 × 10−14 N acting to the right. What is the magnitude of the electric field at the electron’s location?
22. • An electron is acted on by an electric force of 3.2 × 10−14 N. What is the magnitude of the electric field at the electron’s location?
21. IE • (a) If the distance from a charge is doubled, is the magnitude of the electric field (1) increased,(2) decreased, or (3) the same compared to the initial value? (b) If the original electric field due to a charge is 1.0 × 10−4 N/C, what is the magnitude of the new electric field at
20. ••• Two 0.10-g cork balls are suspended from a point by insulating threads each 30 cm long. When the balls are given equal charges, they come to rest 18 cm apart, as shown in ▼ Figure 15.23. What is the magnitude of the charge on each ball? (Neglect the mass of the thread.)
33. •• What is the electric field at the center of the square in Figure 15.22?
47. ••• A small negatively charged cork ball (mass 6.00 × 10−3 g, charge −1.50 nC) is suspended vertically from a light non-conducting string of length 15.5 cm.This apparatus is then placed in a horizontal uniform electric field. After being released, the ball comes to a stable position
46. •• The early twentieth century model of the hydrogen atom pictured the electron as in a circular orbit (radius 5.3 × 10−11 m) with the proton at rest at the center.(a) What is the electric force on the electron? (b) What is the electron’s orbital speed? (c) What is the electron’s
45. •• An pair of identical and initially neutral thin, square metal slabs, measuring 5.00 cm on a side have a 2.00 mm spacing between them. With the slabs oriented horizontally, together they are placed in a vertical uniform external field of field strength 500 N/C. After a few seconds, it is
42. •• A flat, triangular piece of metal with rounded corners has a net positive charge on it. Sketch the charge distribution on the surface and the electric field lines in two dimensions near the surface of the metal(including their direction).
41. •• In Exercise 39, write expressions for the electric field magnitude (a) in the interior of the solid sphere,(b) between the sphere and the shell, (c) inside the shell, and (d) outside the shell. Your answer should be in terms of Q, r (the distance from the center of the sphere), and k.
40. • In Exercise 39, what is the electric field direction(a) in the interior of the solid sphere, (b) between the sphere and the shell, (c) inside the shell, and (d) outside the shell?
38. ••• Two equal and opposite point charges form a dipole, as shown in ▼ Figure 15.24. (a) Add the electric fields due to each end at point P, thus graphically determining the direction of the field there. (b) Derive a symbolic expression for the magnitude of the electric field at point P,
37. ••• Compute the electric field at a point 4.0 cm from q2 along a line running toward q3 in Figure 15.22.
35. •• Two very large parallel plates are oppositely and uniformly charged. If the field between the plates is 1.7 × 106 N/C, (a) how dense is the charge on each plate(in μC/m2)? (b) How much total charge is on each plate if they are 15.0 cm on a side?
19. ••• Four charges are located at the corners of a square, as illustrated in ▼ Figure 15.22. What are the magnitude and the direction of the force (a) on charge q2 and (b) on charge q4?
30. Based on Figure 19.27, approximately how far off (in angle and direction) would your compass direction be from geographic north if you were located in(a) Phoenix, (b) Chicago, and (c) New Orleans?
14. Two parallel straight wires carry different currents in the same direction. Do they attract or repel each other? How do the magnitudes of these forces on each wire compare?
13. (a) Redraw the charged particle path in the apparatus diagrammed in Figure 19.9 if the electric field of the velocity selector were reduced in magnitude.(b) Redraw the charged particle path in the apparatus diagrammed in Figure 19.9 if the magnetic field of the velocity selector were reduced in
12. Redraw the charged particle path in the apparatus diagrammed in Figure 19.9 if the ions were negatively charged instead of positively charged.
11. Explain clearly why the speed selected in a velocity selector setup such as in Figure 19.9 does not depend on the charges of the ions passing through.
10. The circular inset in Figure 19.11 shows how positive sodium (Na+) ions in seawater are accelerated out the rear of the submarine to provide a propulsive force.But what about the negative chlorine (Cl−) ions?Because they have the opposite charge, aren’t they accelerated forward, resulting
9. Explain how particle accelerator operators utilize magnetic fields to “steer” various charged particles in the correction to a specific target for a particular experimental setup.
8. A magnetic field can be used to determine the sign of charge carriers in a current-carrying wire. Consider a wide conducting strip in a magnetic field orientedas shown in ▼ Figure 19.29. The charge carriers are deflected by the magnetic force and accumulate on one side of the strip, giving
7. You want to deflect a positively charged particle in an S-shaped path, as shown in Figure 19.28b, using only magnetic fields. (a) Explain how this could be done by using magnetic fields perpendicular to the plane of the page. (b) How would the emerging particle’s kinetic energy compare with
6. Three particles with the same velocity enter the same uniform magnetic field as shown in ▶ Figure 19.28a.What can you say about (a) the charges of the particles and (b) their masses?
3. (a) As you start in the very middle of Figure 19.3b and move horizontally to the right, what happens to the magnetic field line spacing as indicated by the iron filing pattern? What does this imply for the field strength? (b) What is the direction of the field in this region of the figure? Can
15. Predict what should happen to the length of a metal spring when a large current passes through it. [Hint:Consider the direction of the current in the neighboring spring coils.]
29. In a relatively short time, geologically speaking, data indicate that the Earth’s magnetic field direction will reverse. After that, what would be the polarity of the magnetic pole near the Earth’s geographic North Pole?
28. Determine the direction of the force due to the Earth’s magnetic field on an electron near the equator when the electron’s velocity is (a) due south, (b) northwest, and (c) upward.
27. Suppose the lava flow from the Kilauea volcano on the “Big Island” of Hawaii cools below its Curie temperature as it moves, and finally solidifies. What is the direction of the remnant magnetism in the resulting lava rocks? Explain.
26. Discuss several ways that the magnetic field of a permanent magnet can be destroyed or reversed.
25. What is the purpose of the iron core often used at the center of a solenoid?
24. If you are looking down on the orbital plane of the electron in a hydrogen atom and the electron orbits counterclockwise, what is the direction of the magnetic field the electron produces at the proton?
23. Two circular wire loops are coplanar (their areas are in the same plane) and have a common center. The outer one carries 10 A in the clockwise direction. To create a zero magnetic field at their common center, what should be the direction of the current in the inner loop? Should its current be
22. Wires carrying current to and from an appliance are typically wrapped close together, insulated from each other, and formed into the power cord. Explain how this works to reduce the magnetic field created external to the cord.
20. If you doubled your distance from a long currentcarrying wire, what changes would need to be made to the current to keep the magnetic field strength the same as at the nearer position but reversed direction?
19. A circular current-carrying loop is lying flat on a table.A calibrated compass, when placed at the center of the loop, points toward the ground. If you look straight down on the loop, what is the direction of the current?Explain your reasoning.
26. If the direction of your compass pointed straight up, where would you be: (a) near the Earth’s north geographic pole, (b) near the equator, or (c) near the Earth’s south geographic pole?
10. In a mass spectrometer two ions with identical charge and speed form two different semicircular arcs. Ion A’s arc has a radius of 25.0 cm and ion B’s arc has a radius of 50.0 cm. What can you say about their relative masses: (a) m m A B = , (b) m m A B =2 , (c) m m A B = 12, or(d) you
9. An electron passes through a magnetic field without being deflected. What can you conclude about the magnetic field direction relative to the electron’s velocity, assuming that no other forces act: (a) it could be in the same direction as the velocity, (b) it could be perpendicular to the
8. If a negatively charged particle were moving upward along the right edge of this page, which way should a magnetic field (perpendicular to the plane of the paper) be oriented so that the particle would initially be deflected left: (a) out of the page, (b) in the plane of the page, or (c) into
7. An electron moves horizontally east in a vertical uniform magnetic field. It is found to deflect north.What direction is the field: (a) up, (b) down, or (c) the direction can’t be determined from the given data?
6. A proton moves vertically upward and perpendicular to a uniform magnetic field. It deflects to the left as you watch it. What is the magnetic field direction:(a) directly away from you, (b) directly toward you,(c) to the right, or (d) to the left?
5. Which way would a compass point if placed just to the right of the midway point between the ends of the two magnets in Figure 19.3c: (a) up, (b) down, (c) left, or(d) right?
4. Which way would a compass point if placed midway between the ends of the two bar magnets shown in Figure 19.3b: (a) up, (b) down, (c) left, or (d) right?
3. If you look directly at the south pole of a bar magnet, its magnetic field points (a) to your right, (b) to your left, (c) away from you, (d) toward you.
2. A compass is just above the end of a permanent bar magnet, and points away from that end. It can be concluded that this end acts as (a) a north magnetic pole, (b) a south magnetic pole, (c) you can’t conclude anything about the magnetic properties of that end.
1. When the ends of two bar magnets are close, they attract. These ends must be (a) one north, one south,(b) both north, (c) both south, (d) either (b) or (c).
39. • In Exercise 38, suppose instead the case had been properly wired and grounded as shown in Figure 18.21. (a) If the grounding wire had a resistance of 0.10 Ω, what is the ratio of the current in you to the current in the ground wire, assuming that the fuse/circuit breaker does not
38. • Suppose you are using a drill that is incorrectly wired as in Figure 18.20a, and you make electrical contact with an ungrounded metal case. (a) Explain why this is a dangerous situation for you. (b) Estimate the current in you, assuming an overall body resistance of 300 Ω between your hand
11. In a mass spectrometer two ions with identical mass and speed are accelerated form two different semicircular arcs. Ion A’s arc has a radius of 25.0 cm and ion B’s arc has a radius of 50.0 cm. What can you say about their net charges: (a) q q A B = , (b) q q A B =2 , (c) q q A B = 12, or
12. In the velocity selector shown in Figure 19.9, which way will an ion be deflected if its velocity is less than E/B1:(a) up, (b) down, or (c) there will be no deflection?
25. If a proton orbits just above the Earth’s equator, which way must it be moving for the magnetic force to help the force of gravity: (a) west, (b) east, or (c) either direction?
24. The Earth’s magnetic field (a) has poles that coincide with the geographic poles, (b) only exists at the poles,(c) reverses polarity every few hundred years, (d) none of these.
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