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PHYS 232 QUIZ 102-18-2005

50 minutes.This quiz has 3 questions. Please show all your work. If your final answer is

not correct, you will get partial credit based on your work shown. Youare allowed to have one hand-written, one-sided page of equations.

Question I. (40points)

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2. Two infinite parallel surfaces carry uniform charge densities (0-)of+0.20 nC/ m2and -0.60 nC/ m2 respectively. What is the magnitude ofthe electric field at a point between the two surfaces?

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3. A particle (m =2.0 J-lg,q = -5.0 nC) has a speed of 30 m/ s at point A andmoves (with only electric forces acting on it) to point Bwhere its speedis 80m/ s. Determine the electricpotential difference ~V =VB-VA.

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4. A positively charged particle is moving in the +y-direction when itenters a region with a uniform electric field pointing in the +x-direction. Which of the diagrams below shows its path while it is in theregion where the electric field exists. The region with the field is theregion between the plates bounding each figure. The field lines alwayspoint to the right. The x-direction is to the right; the y-direction is up.

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5. What is the potential difference across C2 when Cl =5.0JlF,C2 =15 JlF, C3 = 30 JlF,and VO = 24 V?

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Question II. (30 points)

A Solid conductingsphere of radius a carries a net negative charge -Q. Concentricwiththis sphere is a conducting sphericalshell with inner radiush and outer radius c, havinganet positive charge +Q.

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1. Describe how the charges are distributed in the sphere and in theconductingshell. Show how you arrived at your answers.

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3. Sketch the variation of the Electric Field as a function of r on the axes here

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5. What is the potential difference between a point on the surface of theconducting sphere (at r=a) and a point on the inside surface of the shell (atr=b) A v fj

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What is the Electric potential just outside the conducting shell ?

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OS- 6. We now fill the space betweenthe sphere and the shell (space"betweena andb) with a dielectric material (K = 3.0). What now is your answer for part 5.above.

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Question III. (30 points)

The circuit shown consists of a 110 v battery with negligible internal resistance, threebulbs BI, B2, and B3 and four switches S1, S2, S3 and S4. Bulbs B I and B2 are rated110 V and 40 W, while bulb B3 is rated 110 V and 100 W. Switches SI, S2 and S3 areclosed while S4 is open.

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R~ := 0\0) -:. 12-1..5L /,C\ 110 /1 f~ 2. Calculate the power dissipated in each bulb. 'R 1.- Ct I-'\.cJ.. R3 f WIfYQ../Ie.-

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1~/3£'<l '" v'ZgA ~) C VOV\...h'Vl~ - - -)3. Calculate the currents through bulbs B2 and B3.

1. Calculate the resistance of each bulb. If= byL-302-' S- SL ~

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Describe what happens to the brightness of each bulb if switch S4 is also

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1>"'* R"t~ R1~ 302-.51- now; >;-0 WlO~+~S~-y\~,'5. A PHYS232 student connects a single light bulb (A) across a regular 9V

battery she bought at the store. Then she adds two more bulbs (B and C), withthe same resistance as A, in parallel with A. Since the new bulbs are added inparallel she expects the brightness of A to remain unchanged. However, theintensity of A goes down when Band C are added. Explain this observation

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