Practice for Test 1, No. 1
1. If you slide your feet across a carpet in the library while you walk, it is possible that when you reach out to touch a metal doorknob, you will feel a shock. This can happen because you have become charged by (a) Conduction. (b) Induction. (c) Friction. (d) Contact. (e) Radiation.
2. Two electric charges are placed nead one another and then released. It is observed that as they move, the acceleration of the particles decreases. The charges are (a) Definitely positive. (b) Definitely negative. (c) One is positive and the other is negative. (d) Both charges must be of the same sign; you cannot say, howver, what that sign is. (e) The situation described is impossible.
3. A location in space is at 0 V. The electric field at that location in space must be (a) 0 N/C. (b) 5 N/C. (c) 10 N/C. (d) 15 N/C. (e) There is not enough information given to answer this question.
4. A capacitor in the form of two concentric cylinders (one inside the other) has a charge Q, voltage V, and a capacitance C. If the charge on one of the plates is doubled, the capacitance will (a) be one-quarter as big. (b) be cut in half. (c) remain the same. (d) be doubled. (e) increase four times.
5. A Two simple circuits have a lamp connected to a 12 v battery. The filaments in each lamp are constructed of the same material and have the same cross-sectional area. The filament of lamp #2 is twice as long as the filament of lamp #1. Which lamp will have the greater power output? (a) Lamp #1. (b) Lamp #2. (c) Since they are connected to identical batteries, the power outputs will be the same. (d) It depends upon which lamp is made by General Electric, because GE lamps are like really good. (e) Not enough information given.
6. A capacitor, a resistor, a switch, and a battery are connected is series with each other. The switch is closed, and the amount of time required for the capacitor to acheive a certain amount of charge. The resistance is then doubled, and the capacitance is cut in half. The new capacitor will achieve the same amount of charge as the first capacitor in (a) one quarter the amount of time. (b) one half the amount of time. (c) the smae amount of time. (d) twice the amount of time. (e) four times as much time.
7. A charge of +1 C is placed at (x=0,y=0) and a -3 C charge is placed at (x=3,y=0 m). In which of the following regions is it possible for a test charge to feel no electric force from the two charges? (A) For x < 0, y = 0. (B) For 0 < x < 3, y = 0. (c) For x > 3, y = 0. (D) For 0 , x < 3, y > 0. (E) It depends upon the sign on the test charge.
8. A conductor differs from an insulator in that a conductor (a) has more electrons than protons. (b) has more protons than electrons. (c) has more energy than an insulator. (d) has faster moving electrons. (e) None of the above.
9. In the Stanford linear accelerator, a beam of electrons is accelerated down a pipe two miles long. Does this beam constitute an electric current? (a) Yes. (b) No, becasue the electrons are not in a conductor. (c) No, because the beam is not electtrically neutral. (d) No, because the beam is electrically neutral. (e) No, becasue only positive charges can form a current.
10. An electronat rest is released. The electron will naturally move from (A) regions of high potential to low potential. (B) regions of low potential to high potential. (C) regions green potential to blue potential. (D) If there is a potential, then there cannot be an electric field. The electron will not move. (E) Depending on the situation, the answer could be either (a) or (b).
11. Two unequal capacitors, initially uncharged, are connected in series across a battery. Which of the following is true? a) The potential across each is the same. b) The charge on each is the same c) The energy stored in each is the same. d) The equivalent capacitance is the sum of the two capacitances. e) None of the above.
12. A parallel plate capacitor is charged by a battery and then disconnected. If now the plates are pulled apart, a) the electric field between the plates will decrease. b) the potential difference between the plates will decrease. c) the charge on the plates will decrease. d) the energy stored in the capacitor will increase. e) All of the above.
13. A negative charge q moves toward the right on the paper you are looking at with a velocity v. A constant magnetic field points directly out of the page. What is the direction fo the magnetic force on the charge? (a) Toward the right. (b) Toward the top of the page. (c) Toward the left. (d) Toward the bottom of the page. (e) There is no magnetic force in this case.
14. Two long, straight wires are separated by a distance d. The wires are parallel to one another. Wire #1 carries a current I1 pointed out of the page, while wire #2 carries a current I2, also out of the page. What is the direction of the magnetic force on wire #2? (a) Toward wire 1. (b) Away from wire 1. (c) Toward the to of the page. (d) Toward the bottom of the page. (e) There is no force on wire #2, wiseguy.
15. Which of the following best explains why some rocks (ie, the ferromagnets) in Magnesia were magnitized? (a) Because the effects of the gravitational force on the atoms in the materials caused an allignment of the magnetics fields associated with each domain. (b) The weight of the magnetic atoms in the material caused them to sink to the bottom of the material. The excess of magnetic atoms at the bottom surface and the deficit of magnetic atoms at the top surface formed the north and south poles. (c) The magnetic field of the earth tends to allign the magneitic fields of the domains over a long period of time. (d) When farmers in Magnesia took milk to the village, their carts rolled over the rocks. The fields from the domains were originally randomly oriented, but as more and more carts rolled over them, the fields got "squished" so that they could only point in the horizontal direction. This allignment produced the magnetic field. (e) It is a weird black hole effect that nobody understands.
16. A point charge possesses a charge of - 4 x 10-9 C. At a distance of 2 m from the charge, the electric field is (a) 9 N/C toward the charge. (b) 18 N/C toward the charge. (c) 9 N/C away from the charge. (d) 18 N/C away from the charge. (e) None of the above.
17. Three 6 µF capacitors are connected in parallel. The effective capacitance of this combination is (a) 0.667 µF. (b) 1 µF. (c) 10 µF. (d) 18 µF. (e) 36 µF.
18. Two metal pieces of stuff in a physics demonstration have 16,000 V of electric potential between them. If the electric field between the pieces of stuff has a vlaue of 48,000 V/m (assumed constant), what is the distance between the pieces of stuff? (a) 32 m. (b) 1/32 m. (c) 1/3 m. (d) 3 m. (e) 1/4 m.
19. Resistor A has twice the resistance of resistor B. They are connected in parallel to a battery. The ratio of the power dissipated by A to that by B is (a) 1/4. (b) 1/2. (c) 1/1. (d) 2/1. (e) 4/1.
20. A straight current carrying wire (cuurent = 1 A) has a length of 1 m, and lies flat on the earth's surface. The earth's magnetic field at the location of the wire is 5 x 10-5 T and is directed at an angle of 30o into the earth (as measured from the surface of the earth) such that the angle between the wire and the magnetic field is also 30 degrees. The magnitude of the force on the wire is (in Newtons) (a) 5.0 x 10-5. (b) 1.0 x 10-5. (c) 2.5 x 10-5. (d) 15.0 x 10-5. (e) 4.33 x 10-5.
21. (a) Three charges are arranges at the corners of an equilateral triangle. The sides of the triangle are each of length 2 m. Charge q1 is placed at (x=-1,y=0) and q2 is placed at (x=1,y=0). Q3 is along the y axis. Calculate the net electric force on the charge q3 due to q1 and q2. q3 = 1 x 10-5 C q1 = 2 x 10-4 C q2 = 2 x 10-4 C (b) How much work was required to bring the charge q3 from infintiy to the point shown above?
22. Two batteries are connected in parallel with a capacitor. The characteristics of each battery is given below, and the capcitiance is also given below. A resistor (value also below) is connected in series with battery #1. The circuit is connected for a time long enough to allow the currents to reach their STEADY STATE values. The batteries should be taken to be real. You will need to draw this circuit! (a) Determine all of the resulting currents. E1 = 5 V r1 = .1 E2 = 10 V r2 = .2 R = 10 C = 6 µF (b) What are the terminal voltages of each battery?
ANSWERS: 1.C 2.D 3.E 4.C 5.A 6.C 7.A 8.E 9.A 10.B 11.B 12.D 13.B 14.A 15.C 16.A 17.D 18.C 19.B 20.C
Practice for Test 1, No. 2
1. Two capacitors are connected in series with a battery. The battery remains connected while a dielectric is slipped between the plates of one of the capacitors. The battery voltage is 12 V. The voltage across the other capacitor after the dielectric is placed between the plates will (a) increase. (b) decrease. (c) remain unchanged. (d) You must know the value of the capacitance to answer this question. (e) equal the energy stored.
2. The device in a circuit which tends to provide the energy needed to maintain a continuous flow of charge is called a (a) Galvinometer. (b) Kickinthepantser. (c) Resistor. (d) Battery. (e) Wire.
3. Coulomb's law deals with (a) the force between two electric charges. (b) the strength of electric currents. (c) the force between two current carrying wire. (d) the energy gained by an electron as it travels from a positive to a negative plate. (e) All of the above.
4. Two charged particles held close to each other are released. As they move, the force on each particle increases. Therefore, the particles have (a) the same sign. (b) the opposite sign. (c) positive charge only. (d) negative charge only. (e) Not enough information given.
5. Electrical potential, measured in volts, is the ratio of electrical energy per amount of electric (a) current. (b) resistance. (c) charge. (d) voltage. (e) None of the above.
6. A parellel plate air capacitor carries a charge Q. If a dielectric slab with dielectric constant k = 2 is slipped between the plates (assume the dielectric fills the space betwen the plates), a) the stored energy remains unchanged. b) the stored energy is increased by a factor of 2. c) the stored energy is reduced by a factor of 2. d) the capacitor will become ferromagnetic. e) None of the above.
7. The copper conductor which would have the least resistance (a) thin, long and hot (b) thick, short and cool (c) thick, long and hot (d) thin, short and cool (e) thin, short and hot
8. Two identical light bulbs are connected in parallel to a battery and the brightness of each is observed. If a third bulb is connected in parallel with the other two, the brightness of the first two bulbs will (a) increase. (b) decrease. (c) remain the same. (d) increase if the third bulb has a larger resistance than the other two. (e) decrease if the third bulb has a larger resistance than the other two.
9. A 100 W light bulb is connected in series with a 50 W light bulb, then both are connected to a 120 V wall socket. Which lamb will have the largest current passing through it? (A) the 100 W bulb. (B) the 50 W bulb. (C) They will both have the same current. (D) It is not possible to have differnt wattage bulbs connected in series. (E) All of the above.
10. As the temperature of a peice of copper wire is increased, it's resistance (A) increases. (B) decreases. © doesn't change. (D) drops to zero. (E) None of hte above.
11. Given a group of nearby charges whose net charge is nonzero, the equipotential surface at a very great distance is (A) nearly a plane. (B) nearly a sphere. (c) nearly a cylinder. (D) undertermined. (E) None of the above.
12. If the charge on each of two identical tiny spheres is doubled while the separation is also doubled, their force of attraction will (A) double. (B) become halved. (c) be quartered. (D) stay unchanged. (E) None of the above.
13. Iron (a ferromagnet) has the special property of containing (a) a north pole. (b) a south pole. (c) domains. (d) both (a) and (b). (e) none of the above.
14.A current carrying wire is perpendicular to the page, with the current coming directly toward you. The wire is between the poles of a magnet, with the north pole to the left of the wire, and the south pole to the right. What is the direction of the magnetic force on the current carrying wire (a) Toward the north pole of the magnet. (b) Toward the south pole of the magnet. (c) Toward the top of the page. (d) Toward the bottom of the page. (e) There is no magnetic force in this case.
15. A charged particle will move in a helix if (a) it is placed in a magnetic field. (b) it is injected into a magnetic field at an angle of 90o with respect to B. (c) it is injected into a magnetic field at an angle of 0o with respect to B. (d) it is injected into a magnetic field at any angle between 0o and 90o (not including 0o or 90o) with respect to B.
16. A three Ohm resistor and a 5 microF capacitor are connected in series with each other. The two of them are connected in parallel with both a 6 Ohm resistor and a 12 V battery. A long time after all of the connections are made, what is the voltage drop across the three Ohm resistor? (a) 6 V. (b) 3 V. (c) 2 V. (d) 1 V. (e) 0 V.
17. Ten capacitors, each of capacitance C, are connected in series. The effective capacitance of the combination is (a) 0.1 C. (b) 10 C. (c) 100 C. (d) 200 C. (e) None of the above.
18. If 10 Amperes circulate in a closed circuit, how much chages passes any point in the circuit in 2 sec? (A) 10 C. (B) 5 C. (C) 20 C. (D) 200 C. (E) All of the above.
19. A battery has a current of 0.1 Amp flowing into the positive terminal of the battery. The internal resistance is .2 Ohm and the emf of the battery is 10.0 V. The terminal voltage of the battery is (A) 10.02 V. (B) 9.98 V. (C) 10.0 V. (D) 0.0 V. (E) There is no terminal voltage, since the situation described cannot happen.
20. A 1 C charge moves through a constant magnetic field of 3 T. The charges velocity is 2 m/sec, and the velocity makes an angle of 30 degrees with the direction of the magnetic field. The force on the charge is (a) 0 N. (b) 1 N. (c) 3 N. (d) 5.196 N. (e) 6 N.
21. A parallel plate capacitor has a plate area of 1 m2, a plate separation of .088 m, and a potential difference between the plates of 8 volts. (a) How much energy is stored in this capacitor? (b) What is the strength of the electric field between the plates? (c) A small positively charged sphere is now placed midway between the plates. Sketch the electric field lines with this charge present. (d) If the charge on the sphere is .1 C and it is placed midway between the plates, what is the resulting force on that charge. Assume the voltage and capacitor geometry is the same as described above.
22. A wire of length 5 m and carrying a current of 2 A is placed in a magnetic field with makes an angle of 60 degrees with repect to the wire. The stength of the magnetic field is 10 T. (a) What is the magnetic force (vector) on the wire? (b) Assume that, instead of a current in a wire, there is an electron moving in the direction above. Take the electrons speed to be 20 m/sec. The resulting motion will be that of a spiral. What is the radius of this spiral? Recall that all centripital forces are of the form mv2/r.
ANSWERS: 1.A 2.D 3.A 4.B 5.C 6.C 7.B 8.C 9.C 10.A 11.B 12.D 13.C 14.C 15.D 16.E 17.A 18.C 19.A 20.C
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