Part B. Three charged particles, each of charge Q=2 Coulombs are placed at the c
ID: 1307117 • Letter: P
Question
Part B. Three charged particles, each of charge Q=2 Coulombs are placed at the corners of an equilateral triangle, as shown in the picture. The triangle sides are 1 m long.
Possible answers are stated in terms of the Coulomb constant. The points S and T are located at the mid point of the sides of the triangle while Y is at the center of the triangle.
(A) -4k (B)-2k (C)0 (D)2k (E) 4k
8. What is the direction of the force on the top charge?
(A) No direction, zero force (B)Left (C)Right (D)Up (E) Down
9. What is the direction of the total electric field at the center of the triangle (point Y)?
(A) No direction, zero field (B)Left (C)Right (D)Up (E) Down
10. What is the direction of the total electric field at the center of the bottom side of the triangle (point T)?
(A) No direction, zero field (B)Left (C)Right (D)Up (E) Down
11. A negative particle is set free, with a certain initial speed, far away from the triangle. It is later observed at position S. Use conservation of energy ideas to identify the correct statement:
(A) The particle has a larger speed at S (than at its initial position)
(B) The particle has a smaller speed at S.
(C) The particle has the same speed at S.
(D) The particle has no speed at S.
(E) More information is needed to determine the relative magnitude of the speed at S.
Part C. Three currents entering or exiting this page, run parallel to each other, as shown in the figure. The three currents have magnitude I. The currents are arranged in a triangular structure. The triangle sides are 1 m long. The points S and T are located at the mid point of the sides of the triangle while Y is at the center of the triangle.
12. What is the direction of the magnetic field acting on the top wire due to the bottom wires?
(A) No direction, zero field (B)Left (C)Right (D)Up (E) Down
13. What is the direction of the magnetic field at the center of the triangle (point Y)?
(A) No direction, zero field (B)Left (C)Right (D)Up (E) Down
14. What is the direction of the magnetic field, due to the three currents, at the midpoint of the bottom side of the triangle (point T)?
(A) No direction, zero field (B)Left (C)Right (D)Up (E) Down
15. What is the direction of the force on the top current due to the bottom wires?
(A) No direction, zero field (B)Left (C)Right (D)Up (E) Down
16. A positive charge moves upwards within the page, just above the top current. What is the direction of the force on this charge?
(A) No direction, zero field (B)Left (C)Right (D)Out of page (E) Into page
17. Which pair of currents experiences a mutual attraction due to their magnetic interaction?
(A) All three pairs of currents.
(B) The pair at the bottom.
(C) The top and left currents.
(D) The top and right currents.
(E) None.
18. Ignoring the small changes in magnetic filed across the rectangle, what is the magnitude of the magnetic flux through the rectangle?
(A) abImo/(2pr) (B) aImo/(2pr) (C) brImo/(2pa)
(D) arImo/(2pb) (E) rImo/(2pab)
19. As the wire moves down the page, which statement best describes the changes in the magnetic field?
(A) It increases in the direction out of the page.
(B) It increases in the direction into the page.
(C) It does not change.
(D) It decreases in the direction out of the page.
(E) It decreases in the direction into the page.
20. The induced electromotive force in the rectangle creates a current. What is the direction of the current?
(A) Circulates clockwise.
(B) Circulates counterclockwise.
(C) It first circulates clockwise then counterclockwise.
(D) It first circulates counterclockwise then clockwise.
(E) More information is needed to determine the circulation direction.
21. At the center of the loop, what is the direction of the magnetic field created by the induced current?
(A) Out of the page.
(B) Into the page.
(C) Left.
(D) Right.
(E) No direction, the field is zero.
22. What is the best description of the relation between the electric and magnetic field in an electromagnetic wave?
(A) They are always parallel, with fixed ratio of magnitudes.
(B) They are always parallel, with independent magnitudes.
(C) They are always perpendicular, with fixed ratio of magnitudes.
(D) They are always perpendicular, with independent magnitudes.
(E) They are perpendicular for sinusoidal waves, but independent in more general cases.
Part E.
An optical system consists of two lenses, the first with a focal length f1=20, and the second with a focal length f2=-20. The position of the object used is specified in each of the questions below. The distance between the lenses is 30. All distances in centimeters.
23. Assume that the object is placed at 30 cm to the left of the first lens as shown in the figure. What is the position of the image created by the first lens?
(A) At the position of lens 2. (B) 30 cm to the right of lens 2.
(C) 10 cm to the left of lens 1. (D) 10 cm to the right of lens 2.
(E) 30 cm to the right of lens 2.
24. Assume that the object is placed in such a way that the image formed by the second lens is located at 20 cm to the right of the second lens. What is the location of the image created by the first lens?
(A) 20 cm to the right of lens 1. (B) 10 cm to the right of lens 1.
(C) 10 cm to the right of lens 2. (D) 5 cm to the right of lens 2.
(E) 5 cm to the left of lens 1.
25. For a particular placement of an object in this system, we obtain magnifications m=-1/2 and m=1/4 after passing through lenses 1 and 2 respectively. If the object has a height of 4 cm, what is the height of the final image in centimeters?
(A) 8 (B) 6 (C) -3 (D) 1/2 (E) -1/2.
26. What is a real image?
(A) One that can be projected on a screen.
(B) One that cannot be projected on a screen.
(C) One from which rays diverge.
(D) One onto which rays converge.
(E) One where the image is oriented in the same way as the object.
This is a practice test for my physics final, I know some of the answers but cant figure some out. Our professor didnt put the answers up. Thanks, I am offering a lot of points for any help.
Explanation / Answer
7. (E) 4k
8. (D)Up
9. (A) No direction, zero field
10. (E) Down
11. (A) The particle has a larger speed at S (than at its initial position)
12. ((E) Down
13. (C)Right
14. (C)Right
15. (D)Up
16. (D)Up
17. (B) The pair at the bottom.
18. (A) abImo/(2pr)
19. (B) It increases in the direction into the page.
20. (B) Circulates counterclockwise.
21. (A) Out of the page.
22. (C) They are always perpendicular, with fixed ratio of magnitudes.
23. (B) 30 cm to the right of lens 2.
24. (A) 20 cm to the right of lens 1.
25. (D) 1/2
26. (A) One that can be projected on a screen.