PHY 106 (Spring 2017): Exam I Directions Feel free to work is out of 20 points.

Question

PHY 106 (Spring 2017): Exam I Directions Feel free to work is out of 20 points. Multiple Choice ouf any problents on scrap pieces of paper or on the exam itself. Be sure to record all your answers in ou are only allowed to use a calculator and the formula sheet. Each question is worth I pt. Exam . You will recieve one point extra credit for writing your name and Ct on the scantron and exam sheeis. any will Identify the choice that best completes the statemeni or answers the question. At one point in space, the clectric potential energy of a 35 nC charge is 65 what is the electric potential at this point? a. 1.9 v b. 19 V C. 190 900 V 2. How many clectrons are necessary to produce 1.0 C of negative charge? a. 6.3 x 1018 b. 6.0 x 1023 I

Explanation / Answer

1. charge q = 35 nC and potential energy is u = 65*10^-6 J

from the relation  

V = W/q = U/q

we know that the potential is v = U/q = 65*10^-6/35*10^-9 V = 1857.143 V = 1900 V

2. Q = 1.0 C

we know that the charge of electron is 1.6*10^-19 C

so Q = N*q

N = Q/q = 1 /(1.6*10^-19) = 6.25*10^18

3.

mass m = 4 g , charge q = -3*10^-6 C

here the gravitaional force is F = mg = Eq

E = mg/q

E = 4*10^-3*9.8 /(3*10^-6) N/C

E = 13066.667 N/C

4. area of the plates is A = 0.03*0.03 m^2

separation is d = 1.5 mm

we knwo the capacitance is C = epsilon not*A/d

C = 8.854*10^-12*(0.03*0.03)/(1.5*10^-3) F

C = 5.3124*10^-12 F

5 . Equivalent capacitance of series of capacitors is  

1/C = 1/c1+1/c2+1/c3

1/C = 1/100 + 1/220 +1/470

C = 59.976 F = 60 F

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