Physics 42 Exam 3 Spring 2016 Name: M T W

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Asher Martin Hines
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Physics 42 Exam 3 Spring 2016 Name: M T W Conceptual Questions & Shorty (2 points each) 1. Which magnetic field causes the observed force? 2. If released from rest, the current loop will move a.

In the frame of the coil, what is the direction of the induced electric field? a. right b. left c. up d. down e. into page f. out of page 4.

1 Physics 42 Exam 3 Spring 2016 Name: M T W Conceptual Questions & Shorty (2 points each) 1. Which magnetic field causes the observed force? 2. If released from rest, the current loop will move a. upward b. downward c. rotate CW d. rotate CCW 3. In the lab frame as shown the coil moves with velocity v into a static magnetic field B. In the frame of the coil, what is the direction of the induced electric field? a. right b. left c. up d. down e. into page f. out of page 4. The three loops of wire shown in the figure are all subject to the same uniform magnetic field that does not vary with time. Loop 1 oscillates back and forth as the bob in a pendulum, loop 2 rotates about a vertical axis, and loop 3 oscillates up and down at the end of a spring. Which loop, or loops, will have an emf induced in them? A) loop 1 B) loop 2 C) loop 3 5. Consider a solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire. If the radius of the solenoid were doubled (becoming 2b), and all other quantities remained the same, the magnetic field inside the solenoid would A) remain the same. B) become twice as strong. C) become one half as strong. 6. In the figure, two solenoids are approaching each other with speed v as shown. The induced current through the resistor R is A) from a to b. B) from b to a. 7. A resistor and an ideal inductor are connected in series to an ideal battery having a constant terminal voltage V0. At the moment contact switch is closed, (a) the voltage across the resistor is A) V0. B) V0/e. C) V0/2. D) zero. (b) the voltage across the inductor is A) V0. B) V0/e. C) V0/2. D) zero. 8. A transformer changes the 10,000 V power line to 120 V. If the primary coil contains 750 turns, how many turns are on the secondary? Show work. Box final answer.. A) 3 B) 6 C) 9 D) 63,000 E) 21,000

2 9. The magnitude of the Poynting vector of a planar electromagnetic wave has an average value of W/m2. What is the maximum value of the magnetic field in the wave? Show work. Box final answer. A) 77.9 nt B) 55.1 nt C) 38.9 nt D) 108 nt E) 156 nt 10. Unpolarized light passes through three polarizing filters. The first one is oriented with a horizontal transmission axis, the second filter has its transmission axis 25.7 from the horizontal, and the third one has a vertical transmission axis. What percent of the light gets through this combination of filters? Show work. Box final answer. A) 0.00% B) 7.6% C) 50.0% D) 92.4% Problems (20 points each.) Show your work. Box final answers. 1. A proton is first accelerated from rest through a potential difference ΔV and then enters a uniform T magnetic field oriented perpendicular to its path, going into the page. The proton follows a circular arc having a radius of curvature of 1.84 cm. What was the potential difference ΔV? Sketch the situation and start Newton s Second Law and conservation of energy to derive the equations you use to solve the problem.

3 2. A segment of wire is formed into the shape shown and carries a current I. Use Bio-Savart Law to find the magnetic field at the point P and express it as a vector. Show all the vectors on the path too. You can use the diagram for that.

4 3. The figure shows the cross-section of a hollow cylinder of inner radius a and outer radius b. A non-uniform current density J = αr with total current I flows through the cylinder parallel to its axis coming out of the page. a. Derive an expression in terms of the given variables (α, a, b, r, etc) for the magnetic field at a distance d from the axis of the cylinder. This is a derivation so justify your steps, draw diagrams, etc. Keep it brief! b. Calculate the magnitude of B for I = 1.00 A, a = 5.00 cm, b = 7.00 cm, d = 10.0 cm

4. A long, straight wire carries a current that is given by I = I max sin(ωt) and lies in the plane of a rectangular coil of N turns of wire, as shown. The quantities I max, and ω, are constants.

5 4. A long, straight wire carries a current that is given by I = I max sin(ωt) and lies in the plane of a rectangular coil of N turns of wire, as shown. The quantities I max, and ω, are constants. Determine the emf induced in the coil by the magnetic field created by the current in the straight wire at the moment t = 5.00s. What is the direction of the induced current? Assume I max = 50.0 A, ω = 200πs 1, N = 100, h = 2.50 cm, w = 5.00 cm, and L = 10.0 cm. Show how the units work out.

PRACTICE EXAM 1 for Midterm 2

PRACTICE EXAM 1 for Midterm 2 Multiple Choice Questions 1) The figure shows three identical lightbulbs connected to a battery having a constant voltage across its terminals. What happens to the brightness