PHY2054 Practice Problems for Final Exam

1. Uncharged cat fur is released near a highly charged metallic sphere. What happens and why?A) The fur falls to the ground, unaffected by the sphere because the fur has a charge of zero.B) The fur is repelled by the sphere because the sphere transfers charge to the fur and like charges repel each other.C) The fur is repelled by the sphere because the sphere induces a like charge in the fur and like charges repel each other.D) The fur is attracted by the sphere because the sphere induces a polarization of charge in the fur, with the opposite charge closer to the sphere than the like charge and opposite charges attract each other.E) The fur is attracted by the sphere because the sphere creates a net opposite charge in the fur and opposite charges attract each other.

2. Two uncharged, conducting spheres, A and B, are held at rest on insulating stands and are in contact. A positively charged rod is brought near sphere A as shown in the figure. While the rod is in place, someone moves sphere B away from A. How will the spheres be charged, if at all?

Sphere A Sphere B

A) Positive PositiveB) Positive NegativeC) Negative PositiveD) Negative NegativeE) Zero Zero

3. The figure shows electrons passing through a resistor. The arrow shows the direction in which the electrons are moving. Three of the following statements are correct. Bubble in all three correct statements to receive credit for this question.

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A) The electrons are moving slower at point b than at point a.B) The electric potential is higher at point b than at point a.C) The electric potential is lower at point b than at point a.D) The electrons are losing electric potential energy as they move through the resistor from a to b.E) The speed of the electrons at point b is the same as it is at point a.

4. If the resistance in a constant voltage circuit is doubled, the power dissipated by that circuit willA) increase by a factor of two.B) increase by a factor of four.C) decrease to one-half its original value.D) decrease to one-fourth its original value.

5. Two equal and opposite charges are a small distance apart, forming an electric dipole. A positive charge +q is placed above these charges, as shown in the figure, equidistant from both of them. Which diagram below best gives the direction of the net force the dipole exerts on the charge +q?

6. The figure shows two unequal charges, +q and -Q. Charge -Q has greater magnitude than charge +q. Point X is midway between the charges. In what section of the line will there be a point where the resultant electric field is zero?

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A) VWB) WXC) XYD) YZ

7. Two point charges are held at the corners of a rectangle as shown in the figure. The lengths of sides of the rectangle are 0.050 m and 0.150 m. Assume that the electric potential is defined to be zero at infinity. Determine the electric potential at corner A.

A) +6.0 x 104 VB) -2.4 x 105 VC) +4.6 x 105 VD) -7.8 x 105 VE) zero volts

8. Two charges of opposite sign and equal magnitude Q = 0.82 C are held 2.0 m apart as shown in the figure. How much work is required to move a 1.0 C charge from infinity to the point P?

A) zero joulesB) 2.2 x 109 JC) 4.5 x 109 JD) 9.0 x 109 JE) infinity9. Which one of the following changes will necessarily increase the capacitance of a capacitor?A) decreasing the charge on the plates

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B) increasing the charge on the platesC) placing a dielectric between the platesD) increasing the potential difference between the platesE) decreasing the potential difference between the plates

10. Two stationary point charges q1 and q2 are shown in the figure along with a sketch of some field lines representing the electric field produced by them. What can you deduce from the sketch?

A) q1 is negative and q2 is positive; the magnitudes are equal.B) q1 and q2 have the same sign; the magnitudes are equal.C) q1 is positive and q2 is negative; the magnitude of q1 is greater than the magnitude of q2.D) q1 is negative and q2 is positive; the magnitude of q1 is less than the magnitude of q2.E) q1 and q2 have the same sign; the magnitude of q1 is greater than the magnitude of q2.

11. As shown in the figure, three small charges are equally spaced on the arc of a circle that is centered at the charge Q, where Q = +23 nC and all the other quantities are accurate to two significant figures. What is the magnitude of the net electric force on the charge Q due to the other three charges? (k = 1/4 0 = 9.0 × 10πε 9 N ∙ m2/C2)

A) 2.6 × 10-4 NB) 1.7 × 10-4 NC) 2.1 × 10-4 ND) 3.1 × 10-4 N

12. A system of four capacitors is connected across a 90-V voltage source as shown in the figure. What is the equivalent capacitance of this system?

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A) 1.5 FμB) 15 FμC) 3.6 FμD) 3.3 FμE) None of the above.

13. What is the equivalent resistance in the circuit shown in the figure?

A) 80 ΩB) 55 ΩC) 50 ΩD) 35 ΩE) None of the above.

14. An electron traveling due south enters a region that contains both a magnetic field and an electric field. The electric field lines point due west. It is observed that the electron continues to travel in a straight line due south. In which direction must the magnetic field lines point?A) upB) downC) eastD) westE) south

15. The figure shows an arrangement of two particles each having charge Q = -6.8 nC and each separated by 5.0 mm from a proton.If the two particles are held fixed at their locations

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and the proton is set into motion as shown, what is the minimum speed the proton needs to totally escape from these particles? (mproton = 1.67 × 10-27 kg, e = 1.60 × 10-19 C, k = 1/4πε0 = 9.0 × 109 N ∙ m2/C2)

A) 2.2 × 106 m/sB) 4.3 × 106 m/sC) 8.3 × 106 m/sD) 1.7 × 107 m/sE) None of the above.

16. A 22-A current flows into a parallel combination of 4.0- , 6.0- , and 12- resistors. Ω Ω ΩWhat current flows through the 12- resistor?ΩA) 18 AB) 11 AC) 7.3 AD) 3.7 AE) None of the above.

17. If V = 20 V and the battery is ideal, what is the current through R3 in the figure?

A) 0.050 AB) 0.20 AC) 1.0 AD) 4.0 AE) None of the above.

18. If you were to cut a small permanent bar magnet in half,A) one piece would be a magnetic north pole and the other piece would be a south pole.

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B) neither piece would be magnetic.C) each piece would in itself be a smaller bar magnet with both north and south poles.D) None of these statements is true.

19. A positive charge is moving to the right and experiences an upward magnetic force, as shown in the figure. In which direction must the magnetic field have a component?

A) to the rightB) to the leftC) upwardD) out of the pageE) into the page

20. An electron, moving horizontally over the ground toward the west, enters a magnetic field. Because of this field the electron curves upward. We may conclude that the magnetic field must have a componentA) towards the north.B) towards the south.C) upward.D) downward.E) towards the west.

21. A negatively charged particle -Q is moving to the right, directly above a wire having a current I flowing to the right, as shown in the figure. In what direction is the magnetic force exerted on the particle due to the current?

A) into the pageB) out of the pageC) downwardD) upwardE) The magnetic force is zero because the velocity is parallel to the current.22. A single current-carrying circular loop of radius R is placed next to a long, straight wire, as shown in the figure. The current I in the wire flows to the right. In which direction must

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current flow in the loop to produce a net magnetic field of zero at its center?

A) counterclockwiseB) clockwiseC) It could be either clockwise or counterclockwise.D) The current in the loop should be zero.

23. A flat circular coil of wire having 200 turns and diameter 6.0 cm carries a current of 7.0 A. It is placed in a magnetic field of 0.60T with the plane of the coil making an angle of 30° with the magnetic field. What is the magnitude of the magnetic torque on the coil?A) 2.1 N ∙ mB) 1.2 N ∙ mC) 3.9 N ∙ mD) 5.4 N ∙ mE) 1.0 N ∙ m

24. The wire in the figure carries a current I that is increasing with time at a constant rate. The wire and the three loops are all in the same plane. What is true about the currents induced in each of the three loops shown?

A) No current is induced in any loop.B) The currents are counterclockwise in all three loops.C) The currents are clockwise in all three loops.D) Loop A has clockwise current, loop B has no induced current, and loop C has counterclockwise current.E) Loop A has counterclockwise current, loop B has no induced current, and loop C has clockwise current.25. As shown in the figure, a coil of wire is placed in the xy-plane, centered on the z-axis. A solenoid is centered on the z-axis and is carrying a steady dc current. Which one of the following actions will not result induce an emf in the coil? There may be more than one

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correct answer. Bubble in all correct answers.

A) Rotate the coil about the x-axis.B) Rotate the coil about the y-axis.C) Rotate the coil about the z-axis.D) Move the coil toward point P.E) Change the current in the solenoid.

26. As shown in the figure, two solenoids are side by side. The switch S is initially open. When S is suddenly closed, the direction of the induced current through the resistor R is

A) from a to b.B) from b to a.C) No current is induced.

27. A transformer changes 120 V across the primary to 2400 V across the secondary. If the secondary coil has 800 turns, how many turns does the primary coil have?A) 40B) 80C) 100D) 400E) 4000

28. A variable capacitor is connected to an ac source. What effect does decreasing the capacitance have on the reactance and current in this circuit?

Reactance Current

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A) No change No change B) Decreases No changeC) Increases IncreasesD) Decreases IncreasesE) Increases Decreases

29. Which circuit elements act to oppose changes in the current in an ac circuit? If there is more than one, mark all to receive credit for this question.A) inductorsB) resistorsC) capacitors

30. What is the inductance of the inductor in a series RCL circuit with a resonant frequency of 640 Hz if the capacitor in the circuit is a 1.2-µF capacitor and the resistor is 13 Ohms?A) 52 mHB) 74 mHC) 0.12 HD) 2.1 HE) 13 H

31. As shown in the figure, a metal bar is in contact with a pair of parallel rails and is in motion with an upward velocity of magnitude . A uniform magnetic field is present, νdirected downward as shown. The direction of the induced current through the resistor R is

A) from a to b.B) from b to a.C) No current is induced.

32. According to Lenz's law, the induced current in a circuit always flows to oppose the external magnetic field through the circuit.A) True

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B) False

33. As shown in the figure, a laser positioned on a ship is used to communicate with a small research submarine resting on the bottom of a lake. The laser is positioned 12 m above the surface of the water, and it strikes the water 20 m from the side of the ship. The water is 58 m deep and has an index of refraction of 1.33. How far horizontally is the submarine from the side of the ship? (Assume all numbers are accurate to three significant figures.)

A) 69 mB) 49 mC) 89 mD) 59 mE) 79 m

I have deleted Problem 34 as it was on RLC Circuit.

35. The figure shows the path of a portion of a ray of light as it passes through three different materials. Note: The figure is drawn to scale.

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What can be concluded concerning the refractive indices of these three materials?A) n1 < n2 < n3

B) n1 > n2 > n3

C) n3 < n1 < n2

D) n2 < n1 < n3

E) n1 < n3 < n2

36. Two identical light waves, A and B, are emitted from different sources and meet at a point P. The distance from the source of A to the point P is LA; and the source of B is a distance LB from P. Which one of the following statements is necessarily true concerning the interference of the two waves?A) A and B will interfere constructively because their amplitudes are the same.B) A and B will interfere constructively if LA = LB.C) A and B will interfere destructively if LA - LB = m where m = 0, 1, 2, 3, ...D) A and B will interfere destructively if LA is not equal to LB.E) A and B will interfere constructively because their wavelengths are the same.

37. A glass block with an index of refraction of 1.7 is immersed in an unknown liquid. A ray of light inside the block undergoes total internal reflection as shown in the figure. Which one of the following relations best indicates what may be concluded concerning the index of refraction of the liquid, nL?

A) nL < 1.0B) nL 1.1C) nL 1.3D) nL 1.1E) nL 1.3

38. In a two-slit experiment, monochromatic coherent light of wavelength 600 nm passes through a pair of slits separated by 2.20x10-5 m. At what angle away from the centerline does the first bright fringe occur?

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A) 1.56°B) 2.22°C) 3.12°D) 4.70°E) 6.24°

39. A light beam with wavelength 500 nm is reflected constructively from a thin layer of oil having index of refraction 1.25. The oil floats on the top of water of index of refraction 1.33. What is the minimum thickness of the layer of oil?A) 100 nmB) 150 nmC) 175 nmD) 200 nmE) 225 nm

40. Two slits separated by 2.00 x 10-5 m are illuminated by light of wavelength 625 nm. If the screen is 6.00 m from the slits, what is the distance between the m = 0 and m = 1 bright fringes?A) 18.8 cmB) 12.5 cmC) 15.6 cmD) 20.3 cmE) 21.4 cm

Questions 41-42 refer to the following diagram. A 4.0-cm object is placed 30.0 cm from a converging lens that has a focal length of 10.0 cm as shown in the diagram. Note: The diagram is not drawn to scale.

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41. Where is the image located?A) 15 cm to the left of the lensB) 7.5 cm to the left of the lensC) 7.5 cm to the right of the lensD) 15 cm to the right of the lensE) 30 cm to the right of the lens

42. Determine the height and orientation of the image.A) 2 cm and uprightB) 1 cm and invertedC) 2 cm and invertedD) 8 cm and uprightE) 8 cm and inverted

43. A drawing is placed 40 cm in front of a thin lens. If a virtual image forms at a distance of 50 cm from the lens, on the same side as the drawing, what is the focal length of the lens?A) -45 cmB) 75 cmC) 90 cmD) 200 cm

44. Which of following statements about the image formed by a single converging lens are true? There could be more than one correct choice. Bubble in all correct choices to get credit for

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this question.A) The image is always real.B) The image is always virtual.C) The image is always inverted.D) The image is always upright.E) None of the above choices are correct.

45. Diffraction occurs when light passes through a single slit. Rank the following three choices in decreasing order, according to the extent of the diffraction that occurs (largest diffraction first):

A - blue light, narrow slitB - red light, narrow slitC - blue light, wide slit

Note: The blue light referred to in choices A and C is the same wavelength. Also, the narrow slit referred to in choices A and B is the same width.A) A, B, CB) B, A, CC) C, A, BD) A, C, BE) B, C, A

46. Name on this form. Name and PID on scantron. PID bubbled in on test form. Exam version bubbled in on scantron. Bubble in A here. All or nothing for 2 easy points.A. I want free points. B. I do not want free points.

47. A thin lens projects an image of a man as shown in the figure. Rays marked A, B, and C travel to the lens from the man's ear. Draw the paths of these three rays after they have passed through the lens. Note that C goes through the focal point on the left, and the point marked f is the focal point on the right of the lens. 3 points.

48. How far apart should two protons be if the electrical force of repulsion on each one is equal to its weight on the earth? Show all work. (mproton = 1.67 × 10-27 kg) 4 points.

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49. Three very long, straight, parallel wires each carry currents of 4.0 A, directed out of the page as shown in the figure. These wires pass through the vertices of a right isosceles triangle as shown. Assume that all the quantities shown in the figure are accurate to two significant figures. What is the magnitude of the magnetic field at point P at the midpoint of the hypotenuse of the triangle? (μ0 = 4 × 10π -7 T ∙ m/A) Show all work. Also indicate the direction of the magnetic field at P with a vector, and provide the angle of the vector from the +X axis (to the right). 8 points.

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