Physics

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Summer 2007 Physics 212 Hour Exam 2 (25 questions)
The grading button and a description of the scoring criteria are at the bottom of this page. Basic questions are marked by a single star *. More difficult questions are marked by two stars **. The most challenging questions are marked by three stars ***. True-false questions are worth 2 points each, three-choice multiple choice questions areworth 3 points each, five-choice multiple choice questions are worth 6 points each. The maximum possible score is 100. The exam period was 90 minutes; the mean was 59.1; the median was 59. Click here to see page1 page2 of the formula sheet that came with the exam.

QUESTION 1***
When two identical resistors are connected in parallel across the terminals of a battery, the power delivered by thebattery is 10 watts. If these resistors are instead connected in series across the terminals of the same battery, what is the power delivered by the battery? (a) 2.5 W (b) 5 W (c) 10 W (d) 20 W (e) 40 W

QUESTION 2*
This and the next question refer to the situation described here. The resistance of the lamp is 70 Ω (assume this is constant). Initially both capacitors are uncharged, and switch S1is open. The switch S1 is then closed. Just after switch S1 is closed, what is the battery

current? (a) 0 A (b) 0.089 A (c) 0.12 A (d) 0.24 A (e) none of the above

QUESTION 3**
Which one of the following could be a graph of the brightness of the bulb, proportional to the power dissipated in the bulb?

(a) (b) (c)

QUES TION 4**
This and the next

question refer to the situationdescribed here. Fig. A: A square loop of sides a = 10 cm lies in the x-z plane with current I = 2 amps as shown. The loop is free to rotate about the x-axis without friction. A uniform magnetic field, B = 1.5 T points in the positive z direction. A person sits on the positive x-axis, looking toward the square loop at the origin. Fig. B: the square loop is rotated by 30 degrees from the z-axis inclockwise fashion. The dotted line is perpendicular to the plane of the loop. The torque on the wire loop in Fig. A. is (a) zero, and hence the loop will not tend to rotate. (b) along the negative x-axis tending to make the loop rotate clockwise as viewed by the observer. (c) along the negative x-axis tending to make the loop rotate counterclockwise as viewed by the observer. (d) along the positivex-axis tending to make the loop rotate clockwise as viewed by the observer. (e) along the positive x-axis tending to make the loop rotate counterclockwise as viewed by the observer. (see Fig. B)

QUESTION 5***
To rotate the wire loop 30° clockwise (see Fig. B) requires how much work by an external agent? (Positive is defined as inputting energy.) (a) +0.026 J (b) -0.026 J (c) +0.015 J (d) -0.015 J(e) 0 J

QUESTION 6**
An infinitely long coaxial cable consists of a solid conducting cylinder of radius R1 = 1 mm and a hollow conducting shell with inner radius R2 = 2 mm and outer radius R3 = 3 mm. The cable is

aligned along the z axis, and centered at x = y = 0. The inner conductor carries a uniformly distributed current I1 = 2 A in the +z direction (out of the page) and the conductingshell carries a uniformly distributed current of I2 = 5 A in the -z direction (into the page). The magnetic field at the point P is 0 (P is not necessarily shown to scale). How far is P from the center of the cable? (a) 2.00 mm (b) 2.40 mm (c) 2.45 mm

QUESTION 7**
This and the next question refer to the situation described here. A single wire is wrapped into a coil with 200 turns and diameter10 cm (see figures). The axis of the coil is aligned vertically. The coil is placed in a uniform magnetic field of magnitude 2.0 T in the upward direction. The direction of the field is suddenly reversed during a time interval of 0.2 s.

During the reversal, the current flows in the clockwise direction.

(T) True (F) False

QUESTION 8***
Find the average emf in the coil during the...

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