phy2054_S23_exam1_Unannotated

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Exam #77777 Exam #77777 Directions 1. Print your name on this question sheet and sign it. 2. Code your 5-digit exam code (at the top of this question sheet) on your Scantron in columns 76–80. 3. Code your name and 8-digit UFID on the Scantron. Darken all circles completely on the Scantron using a #2 pencil or dark blue or black ink. Do not make any stray marks or the Scantron may not read properly. 4. Do all scratch work anywhere on this question sheet that you like. At the end of the exam, the question sheet and Scantron are both to be turned in. No credit will be given without both Scantron sheet and question sheet. 5. The answers are rounded, so choose the closest to exact. There is no penalty for guessing. 1. Which of the following statements, regarding the exam directions on the first page, is true? I. The exam code shown at the top corner of the exam page must be bubbled in lines 76-80 II. According to direction 9, you are allowed to take home both the exam questions and scratch paper III. Students are required to print and sign their names at the top of the exam’s front page (1) I only (2) II only (3) I and II only (4) I and III only (5) I, II, and III 2. A system consists of a positive charge + q released from rest near a fixed positive charge + Q . The two charges are isolated from their surroundings. Which statements are correct about the motion of the released charge while there is some separation between them? I. It accelerates in the direction opposite to the electric field. II. The magnitude of the acceleration is decreasing. III. Its speed will continually increase. (1) I only (2) II only (3) I and III only (4) III only (5) II and III only. 3. A system consists of a negative charge - q released from rest near a fixed positive charge + Q . The two charges are isolated from their surroundings. Which statements are correct about the motion of the released charge while there is some separation between them? I. It accelerates in the direction opposite to the electric field. II. The magnitude of the acceleration is decreasing. III. Its speed will continually increase. (1) I only (2) II only (3) I and III only (4) III only (5) I, II, and III. 4. A small plastic sphere is charged to +2 . 0 nC. It is held 3.00 cm directly above a small glass bead at rest on a table. The bead has a mass of 15.0 mg and a charge of +3 . 0 nC. What is the magnitude of the normal force acting on the glass bead by the table? (1) 150 μ N (2) 90 μ N (3) 60 μ N (4) 120 μ N (5) 210 μ N 5. A small plastic sphere is charged to - 3 . 0 nC. It is held 3.00 cm directly above a small glass bead at rest on a table. The bead has a mass of 15.0 mg and a charge of +2 . 0 nC. What is the magnitude of the normal force acting on the glass bead by the table? (1) 150 μ N (2) 90 μ N (3) 60 μ N (4) 120 μ N (5) 210 μ N 6. It is observed that the electric field at the origin is 0. Which statement could be true based on this information? I. There are no charges in the proximity of the origin II. There is an equal amount of positive and negative charges above/below the x-axis, respectively III. There is a net positive charge along the x-axis (1) I only (2) II only (3) I and II only (4) I and III only (5) I, II, and III

Exam #77777 Exam #77777 7. Four tiny charged particles (two having a charge + Q and two having a charge - Q ) are fixed in place at locations on the xy plane as shown. Each charge is equidistant from the origin. In which direction is the net electric field at the point P ? Upwards means along the + y direction and downwards means along the - y direction. (1) directly upwards (2) to the left (3) upwards and towards the left (4) upwards and towards the right (5) The net field is zero, so there is no direction. 8. Four tiny charged particles (two having a charge + Q and two having a charge - Q ) are fixed in place at locations on the xy plane as shown. Each charge is equidistant from the origin. In which direction is the net electric field at the point P ? Upwards means along the + y direction and downwards means along the - y direction. (1) directly upwards (2) to the right (3) upwards and towards the left (4) upwards and towards the right (5) The net field is zero, so there is no direction. 9. Two parallel plate capacitors with an area of A 1 = 0 . 1 cm 2 , A 2 = 0 . 05 cm 2 and charges q 1 = q 2 = 2 . 0 pC . Both have an electrode separation of d = 0 . 02 mm. If the capacitors are brought into contact with each other to form a single capacitor (as shown in the figure), what is the final magnitude of the electric field between the plates? + + + + + + + + - - - - - - - - (1) 3 . 0 × 10 4 V/m (2) 1 . 5 × 10 4 V/m (3) 2 . 3 × 10 4 V/m (4) q 1 ε 0 A 1 + q 2 ε 0 A 2 (5) All other choices are incorrect. 10. Two parallel plate capacitors with an area of A 1 = 0 . 1 cm 2 , A 2 = 0 . 05 cm 2 and charges q 1 = q 2 = 4 . 0 pC . Both have an electrode separation of d = 0 . 02 mm. If the capacitors are brought into contact with each other to form a single capacitor (as shown in the figure), what is the final magnitude of the electric field between the plates? + + + + + + + + - - - - - - - - (1) 6 . 0 × 10 4 V/m (2) 3 . 0 × 10 4 V/m (3) 4 . 5 × 10 4 V/m (4) q 1 ε 0 A 1 + q 2 ε 0 A 2 (5) All other choices are incorrect. 11. A charge Q starts at point A and is moved along the dashed path to points B, C, and finally arriving at D, in the presence of a uniform electric field of magnitude 500 V/m and direction as shown in the figure. What is the change in potential that the charge undergoes? (1) 0 V (2) +9 V (3) - 16 V (4) +20 V (5) Depends on the sign of Q E A B C D 1 cm

Exam #77777 Exam #77777 12. A charge Q starts at point A and is moved along the dashed path to points B, C, and finally arriving at D, in the presence of a uniform electric field of magnitude 500 V/m and direction as shown in the figure. What is the change in potential that the charge undergoes? (1) 0 V (2) - 9 V (3) +16 V (4) - 20 V (5) Depends on the sign of Q E A B C D 1 cm 13. The V vs y graph shows the values of electric potential in a region of space where the electric field points in the + y direction or - y direction and no other orientations are observed. Based on the graph, at which labeled location(s) along the y -axis is the magnitude of the electric field the the smallest? (1) M only (2) M and O only (3) N only (4) O only (5) All other choices are incorrect. +V –V y M N O 14. The V vs y graph shows the values of electric potential in a region of space where the electric field points in the + y direction or - y direction and no other orientations are observed. Based on the graph, at which labeled location(s) along the y -axis is the magnitude of the electric field the largest? (1) M only (2) M and O only (3) N only (4) M, N, and O (5) All other choices are incorrect. +V –V y M N O 15. A negative charge, with unknown magnitude Q and M = 2 . 5 × 10 - 20 kg, is placed halfway between two positive charges (with q A = +7 nC, q B = +12 nC, and m A = m B = 5 . 5 × 10 - 18 kg separated by a distance 2 d = 10 cm as shown in the figure. The negative charge is then moved to a final location a distance d to the right of the positive charge A. The net change in the potential energy of the system is x q A q B Q d d (1) Positive (2) Negative (3) Zero (4) Depends on the magnitude of Q (5) Cannot be determined

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Exam #77777 Exam #77777 16. A negative charge, with unknown magnitude Q and M = 5 . 0 × 10 - 20 kg, is placed halfway between two positive charges (with q A = +12 nC, q B = +7 nC, and m A = m B = 15 . 5 × 10 - 18 kg separated by a distance 2 d = 10 cm as shown in the figure. The negative charge is then moved to a final location a distance d to the right of the positive charge A. The net change in the potential energy of the system is x q A q B Q d d (1) Positive (2) Negative (3) Zero (4) Depends on the magnitude of Q (5) Cannot be determined 17. The RHIC at Brookhaven National Laboratory can accelerate and collide heavy nuclei such as gold to study the underlying physics of subatomic particles. If two fully ionized gold nuclei (where the element number Z of gold is Z = 79), with a mass of 3 . 3 × 10 - 25 kg and whose radii are 4 . 1 fm are moving towards each other with a speed of 2 . 0 × 10 7 m/s each, will they collide, or if not what is the distance of closest approach that they will reach? (1) 11 fm (2) 22 fm (3) 870 fm (4) The nuclei will collide. (5) All other choices are incorrect. 18. The RHIC at Brookhaven National Laboratory can accelerate and collide heavy nuclei such as iron to study the underlying physics of subatomic particles. If two fully ionized iron nuclei (where the element number Z of iron is Z = 26), with a mass of 9 . 3 × 10 - 26 kg and whose radii are 1 . 9 fm are moving towards each other with a speed of 2 . 0 × 10 7 m/s each, will they collide, or if not what is the distance of closest approach that they will reach? (1) 4.2 fm (2) 8.4 fm (3) 110 fm (4) The nuclei will collide. (5) All other choices are incorrect. 19. The RHIC at Brookhaven National Laboratory can accelerate and collide heavy nuclei such as oxygen to study the underlying physics of subatomic particles. If two fully ionized oxygen nuclei (where the element number Z of oxygen is Z = 8), with a mass of 2 . 7 × 10 - 26 kg and whose radii are 0 . 51 fm are moving towards each other with a speed of 2 . 0 × 10 7 m/s each, will they collide, or if not what is the distance of closest approach that they will reach? (1) 1.4 fm (2) 2.8 fm (3) 11 fm (4) The nuclei will collide. (5) All other choices are incorrect. 20. Each plate of a capacitor remains connected to a 9V battery with ideal wires while its plates are pulled further apart. Which of the following are true of the process? I. The electric field between the plates decreases. II. The energy stored in the capacitor remains the same. III. Charge on the plates increases. (1) I and II only (2) I and III only (3) II only (4) II and III only (5) All other choices are incorrect. 21. Each plate of a capacitor remains connected to the terminals of a 9V battery with ideal wires while its plates are pushed closer together. Which of the following are true of the process? I. The electric field between the plates decreases. II. The energy stored in the capacitor remains the same. III. Charge on the plates increases. (1) I only (2) I and III only (3) II only (4) II and III only (5) All other choices are incorrect. 22. A stream of charged Styrofoam beads, with mass m = 0 . 1 g and charge q = 2 . 0 pC each, are flowing through a pipe at a speed of v = 0 . 1 mm/s. There are 1000 beads/cm 3 throughout the pipe, which has a circular cross-sectional with radius r = 1 cm, and length L = 50 cm. There is a uniform electric field with magnitude | E | = 2 N/C within the pipe. What is the resistance of the pipe? (1) 1 . 6 × 10 10 Ω (2) 3 . 2 × 10 8 Ω (3) 0 Ω (4) E qnπr 2 vL (5) E qnrv

Exam #77777 Exam #77777 23. What happens to the speed of the beads and the potential difference between the ends of the pipe if the diameter of the pipe is doubled, while keeping the current the same? Speed of beads Potential Difference (1) Increases Increases (2) Decreases Increases (3) Increases Decreases (4) Decreases Decreases (5) Increases Remains Unchanged 24. A stream of charged Styrofoam beads, with mass m = 0 . 1 g and charge q = 2 . 0 pC each, are flowing through a pipe at a speed of v = 0 . 1 mm/s. There are 50000 beads/cm 3 throughout the pipe, which has a circular cross-sectional with radius r = 1 cm, and length L = 50 cm. There is a uniform electric field with magnitude | E | = 2 N/C within the pipe. What is the resistance of the pipe? (1) 3 . 2 × 10 8 Ω (2) 6 . 4 × 10 6 Ω (3) 0 Ω (4) E qnπr 2 vL (5) E qnrv 25. What happens to the speed of the beads and the potential difference between the ends of the pipe if the diameter of the pipe is halved, while keeping the current the same? Speed of beads Potential Difference (1) Increases Increases (2) Decreases Increases (3) Increases Decreases (4) Decreases Decreases (5) Increases Remains Unchanged 26. A 5.0 V battery stores 43 kJ of energy and supplies 1.5 A of current to a bulb through ideal wires. How much energy does the battery have left after lighting the bulb for half an hour? (1) 30 kJ (2) 14 kJ (3) 36 kJ (4) 7.5 kJ (5) 39 kJ 27. A 5.0 V battery stores 43 kJ of energy and supplies 1.5 A of current to a bulb through ideal wires. How much energy does the battery have left after lighting the bulb for 1.5 hours? (1) 2.5 kJ (2) 41 kJ (3) 36 kJ (4) 15 kJ (5) 28 kJ 28. Two wire segments, each made of different materials with resistivities ρ 1 and ρ 2 , are joined to form a conductor. Each segment has equal lengths and diameters. A current I passes through wire segment 1. If the ratio of the resistivities ρ 1 /ρ 2 = 2 . 0, what is the ratio of the power dissipated by each wire segment P 1 /P 2 ? (1) 1.0 (2) 2.0 (3) 0.5 (4) 0.25 (5) 4.0 ρ 1 ρ 2 29. Two wire segments, each made of different materials with resistivities ρ 1 and ρ 2 , are joined to form a conductor. Each segment has equal lengths and diameters. A current I passes through wire segment 1. If the ratio of the resistivities ρ 1 /ρ 2 = 0 . 5, what is the ratio of the power dissipated by each wire segment P 1 /P 2 ? (1) 1.0 (2) 2.0 (3) 0.5 (4) 0.25 (5) 4.0 ρ 1 ρ 2 >>>>>>>> END OF EXAM <<<<<<<< Proofread your ANSWER FORM Rows 1-15 contain only one bubbled answer in each row, corresponding to your intended response. Rows 76-80 contain your test form number. Your name and UFID are bubbled.

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Exam #77777 Exam #77777 Exam 1 Reference Sheet Kinematics and Geometry Fundamental Principles Fundamental Constants Prefixes f p n µ m c k M G Δ ⃗ p = ⃗ F net Δ t ⃗ p = m ⃗ v ⃗ F net = m ⃗ a v f , x = v i , x + a x Δ t v 2 f , x = v 2 i , x + 2 a x Δ x x f = x i + v i , x Δ t + 1 2 a x ( Δ t ) 2 x f = x i + v x Δ t A circ = π R 2 A sphere = 4 π R 2 ⃗ F el = q ⃗ E net F g = mg Δ U el = q Δ V K = 1 2 mv 2 E Q = 1 4 πϵ 0 Q r 2 E cap = Q / A ϵ 0 E = Δ V d V Q = 1 4 πϵ 0 Q r Δ V = IR I = Δ q Δ t = neAv d C = κϵ 0 A d Q = C Δ V R = ρ L A U cap = 1 2 C ( Δ V ) 2 u E = 1 2 κϵ 0 E 2 g = 9.8 m/s 2 k = 8.99 × 10 9 Nm 2 /C 2 ϵ 0 = 8.85 × 10 − 12 C 2 /(Nm 2 ) m electron = 9.11 × 10 − 31 kg m n ≈ m p = 1.67 × 10 − 27 kg e = 1.60 × 10 − 19 C Δ U el = − W field F el = k qQ r 2 10 − 15 10 − 12 10 − 9 10 − 6 10 − 3 10 − 2 10 3 10 6 10 9 P = I Δ V = Δ U Δ t 1eV = 1.60 × 10 − 19 J a c = v 2 R Electrostatics Circuits Δ V = − ⃗ E ⋅ ⃗ x = − Ex cos θ

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