PSI AP Physics C Sources of Magnetic Field. Multiple Choice Questions

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1 PSI AP Physics C Sources of Magnetic Field Multiple Choice Questions 1. Two protons move parallel to x- axis in opposite directions at the same speed v. What is the direction of the magnetic force on the upper proton? (A) to the right (B) to the left (C) out of the page (D) into the page (E) to the top of the page 2. A positive charge q moves at a constant speed v in the direction presented by the above diagram. What is the direction of the magnetic field due to the moving charge at point P? (A) to the right (B) to the left (C) out of the page (D) into the page (E) to the top of the page 3. A negative charge q moves at a constant speed v in the direction presented by the above diagram. What is the direction of the magnetic field due to the moving charge at point P? (A) to the right (B) to the left (C) out of the page (D) into the page (E) to the bottom of the page

2 4. A positive charge q moves at a constant speed v parallel to the x-axis. At which of the following points is the magnetic field strongest in magnitude? (A) A (B) B (C) C (D) D (E) E 5. Two positive charges of equal magnitude move in a reference frame shown on the above diagram. What is the direction of the net magnetic field at the origin? (A) into the page (B) out of the page (C) to the left (D) to the right (E) zero 6. Two opposite charges of equal magnitude move in a reference frame shown on the diagram. What is the direction of the net magnetic field at the origin? (A) into the page (B) out of the page (C) to the left (D) to the right (E) zero

3 7. A long, straight wire, shown above, carries an electric current I. What is the direction of the magnetic field at point P? (A) into the page (B) out of the page (C) to the right (D) to the left (E) to the top of the page 8. A long, straight wire carries an electric current I directed into the page. If B 0 is the magnitude of magnetic field due the current at point A, what is the magnitude of the field at point B? (A) 2B 0 (B) 4B 0 (C) B 0 (D) B 0 2 (E) B Two long, straight wires carry equal currents directed into the page. What is the direction of the magnetic field at the midpoint between the wires? (A) into the page (B) out of the page (C) to the top of the page (D) to the bottom of the page (E) zero

4 10. Two long, straight wires carry equal currents directed into the page. The wires are placed at two corners of an equilateral triangle. Which of the following is the correct direction of the net magnetic field at point P? (A) (B) (C) (D) (E) 11. Two long, straight wires carry equal, but opposite, currents perpendicular to the page as shown above. The wires are placed at two corners of an equilateral triangle. Which of the following is the correct direction of the net magnetic field at point P? (B) (B) (C) (D) (E)

5 12. Two long, straight wires carry equal but opposite currents perpendicular to the page as shown above. If B 0 is the magnitude of the magnetic field due to each current at distance r from the wire, what is the net magnetic field at point P due to the two currents in terms of B 0? (A) B 0 6 (B) B 0 5 (C) 5B 0 6 (D) B 0 3 (E) 7B Two long, straight wires carry equal currents perpendicular to the page as shown above. If B 0 is the magnitude of the magnetic field due to each current at distance r from the wire, what is the net magnetic field at point P due to two currents in terms of B 0? (A) B 0 6 (B) B 0 5 (C) 5B 0 6 (D) B 0 3 (E) 7B Two long, straight wires carry equal currents perpendicular to the page. There is an attractive magnetic force between the wires of magnitude F 0. What is the new force between the wires if the magnitude of each current is doubled? (A) 2F 0 (B) 3F 0 (C) 4F 0 (D) F 0 2 (E) F Two long, straight wires carry equal currents perpendicular to the page. There is an attractive magnetic force between the wires of magnitude F 0. What is the new force between the wires if the distance between the wires is doubled? (B) 2F 0 (B) 3F 0 (C) 4F 0 (D) F 0 2 (E) F 0 4

6 16. Three parallel wires are each carrying a current I in the direction shown on the diagram. What is the direction of the net magnetic force on the bottom wire? (A) out of the page (B) into the page (C) to the top of the page (D) to the bottom of the page (E) zero 17. Two circular loops of wire each carry a current I. Loop A has twice the radius of loop B. What is the ratio of the magnetic field at the center of loop A to that of loop B? (A) 2 (B) 4 (C) 1 1 (D) (E)

7 18. A circular conductor carries an electric current I. The loop is placed in the x-y-z reference frame in such way that the center of the loop is at the origin. The plane of the loop is parallel to the y-z axes and perpendicular to the x-axis. Which one of the following graphs represents the magnetic field strength along the x-axis? (A) (B) (C) (D) (E)

8 19. An electric current I passes through a wire with a semicircular section of radius a. What is the magnitude of the magnetic field at point P? (A) μ 0 I (B) μ 0 I 2a (C) μ 0I a (D) 3μ 0I (E) 5μ 0I 20. What is the magnitude of the magnetic field at point P due to two equal currents passing in the same direction through semicircular loops with one common center? (A) μ 0 I (B) μ 0 I 2a (C) μ 0 I a (D) 3μ 0I (E) zero 21. What is the magnitude of the magnetic field at point P due to two equal currents passing in opposite directions through semicircular loops with one common center? (A) μ 0 I (B) μ 0 I 2a (C) μ 0I a (D) 3μ 0I (E) zero

22. What is the magnitude of the magnetic field at point P due to the electric current I passing through a wire that curves into two semicircular loops as shown above?

9 22. What is the magnitude of the magnetic field at point P due to the electric current I passing through a wire that curves into two semicircular loops as shown above? (A) μ 0 I (B) μ 0 I 2a (C) μ 0I 8a (D) 3μ 0I (E) zero 23. A uniform magnetic field B is created by the electric current flowing through a long solenoid. What is the magnitude of the magnetic field inside the solenoid with the same current and twice the radius? (A) B (B) 2B (C) 3B (D) B 2 (E) B A cylindrical conductor with a radius a carries an electric current I. The current is uniformly distributed over the cross-sectional arear of the cylinder. What is the magnetic field B in the region r<a? (A) μ 0 I πa (B) μ 0 I (C) μ 0 Ir 8πa 2πa 2 (D) μ 0 I (E) μ 0 I 4πa 2πa

10 25. A cylindrical conductor with radius a carries an electric current I. The current is uniformly distributed over the cross-sectional arear of the cylinder. What is the magnetic field B in the region r>a? (A) μ 0 I πa (B) μ 0I 8πa (C) μ 0Ir 2πa 2 (D) μ 0I 4πr (E) μ 0I 2πr 26. A uniform magnetic field B is created by an electric current I flowing through a long solenoid with n turns per unit length and radius R. What is the magnitude of the magnetic field inside the solenoid? (B) μ 0 nir (B) μ 0 nir 2 (C) μ 0nI (D) μ 0nI R R 2 (E) μ 0 ni

11 27. A cylindrical conductor with radius a carries an electric current I. The current is uniformly distributed over the cross-sectional area of the cylinder. Which of the following graphs represents the magnetic field B as a function of distance r, both inside and outside the conductor? (A) (B) (C) (D) (E)

12 28. A solid conductor with radius a is surrounded by a tube with an inner radius b and outer radius c. The conductor and tube carry equal currents in opposite directions (conductor - out of the page, tube - into the page). An electron e travels to the right in the space between the conductor and tube at point P. What is the direction of the magnetic force on the electron at point P? (A) Into the page (B) out of the page (C) to the bottom of the page (D) to the top of the page (E) to the left 29. A solid conductor with radius a is surrounded by a tube with an inner radius b and outer radius c. The conductor and tube carry equal currents in opposite directions (conductor - out of the page, tube - into the page). What is the magnitude of the magnetic field in the space between the conductor and tube where a<r<b? μ 0 I (A) (B) μ 0I (C) μ 0Ir πr 2πr 2πa 2 (D) μ 0I 4πa (E) μ 0I 16πr

13 30. A solid conductor with radius a is surrounded by a tube with an inner radius b and outer radius c. The conductor and tube carry equal currents in opposite directions (conductor - out of the page, tube - into the page). What is the magnitude of the magnetic field outside the tube where r>c? (A) μ 0 I πr (B) μ 0I 2πr (C) μ 0Ir 2πa 2 (D) μ 0I 4πa (E) zero

14 Answer Key 1. E 6. B 11. D 16. D 21. B 26. E 2. C 7. A 12. A 17. D 22. C 27. C 3. D 8. E 13. C 18. C 23. A 28. A 4. D 9. E 14. C 19. A 24. C 29. B 5. E 10. A 15. D 20. E 25. E 30.E

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