Be sure to turn off all cell phones, tablets, and laptops. Do not use a phone, t

Question

Be sure to turn off all cell phones, tablets, and laptops. Do not use a phone, tablet, or laptop as a calculator. Do not share a calculator with a neighbor. Once you start the exam without submitting your exam do not leave the room Multiple Choice Section: (5 points each) 1. An electroscope, such as the one shown, is grounded as your finger touches the metal disk and the gold foil leaf falls straight down. A glass rod is rubbed with silk and made to touch the conducting disk of the electroscope. The gold foil rises to an angle of 45 degrees and remains so after the glass rod is taken away. By this we know that the electroscope is A) charged negatively B) charged positively neutral polarized A small copper metal spherical ball with a radius of 8 mm is insulated and given a 6 nC positive charge. What is the strength of the electric field 10 cm from the center of the ball? 2. A) 540 N/c B) 2400 N/C C) 5400 N/C D) 21600 N/C 3. The same small metal ball charged as in the previous problem has uniform surface voltage of A) 3375 V B) 6750 V C) 211 kV D) 844 kV A 12.0 C negative charge is released from rest and is attracted to a large positive charge. The negative charge moves through a potential difference of 4 mV. How much kinetic energy does the negatively charged object obtain? 4. )033 B) 48 n D) 72 n

Explanation / Answer

1.

when the glass rod is rubbed with silk, then the glas rod becomes positively charged because looses electrons  

when the glass rod touches the metal disc then the gold foil makes 45 degrees means the repulsive force  

so the electroscope is positively charged answer is option (B)

2. E = kq/r^2 = 9*10^9*6*10^-9/(0.1^2) N/C = 5400 N/C ===> answer is option (C)

3. V = kq/r = 9*10^9*6*10^-9/(0.008) V = 6750 v ===> answer is option B  

4. Given

q = 12*10^-6 C , V = 4 mV

V = W/q = dK.e/q

d k.e = V*q

d k.e = 4*10^-3*12*10^-6 J

d k.e = 4.8*10^-8 J

d k.e = 48*10^-9 J

answeris option B

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