1. Find the electrical potential at 0.15 m from a point charge of 0.90 µ C. ( ke

Question

1. Find the electrical potential at 0.15 m from a point charge of 0.90 µC.
(ke = 8.99 · 109 N·m2/C2)

2.

A point charge of +4.60 nC is located at the origin of a coordinate system and a second point charge of -3.50 nC is at

3. A parallel-plate capacitor has a capacitance of 20 µF. What potential difference across the plates is required to store 7.2 · 10 -4 C on this capacitor?

4. Two capacitors with capacitances of 13.1 and 18.1 µF, respectively, are connected in parallel. The system is connected to a 15-V battery. What charge accumulates on the 18.1-µF capacitor?
Give your answer in µC.

6. A 1.680 -µF capacitor is connected to a 410-V battery. What potential energy (in Joules) is stored in the capacitor?

7. The dielectric strength of Rutile is 6.0 ´ 106 V/m, which corresponds to the maximum electric field that the dielectric can sustain before breakdown. What is the maximum charge that a 10-10-F capacitor with a 1.0-mm thickness of Rutile can hold?

Explanation / Answer

1) r = 0.15 m , Q = 0.9 uC

V = kq/r

V = 9*10^9*0.9*10^-6/0.15

v= 54000 v

2) q1 = 4.6 nC , q2 = -3.5 nC ,

V = V1 +V2

V =(9*10^9*4.6*10^-9/0.57) -(9*10^9*3.5*10^-9/(1.8-0.57))

V = 47 V

3) C = 20 uF, Q = 7.2*10^-4 C

Q = VC

7.2*10^-4 = V*20*10^-6

V = 36 V

4) C12 = 13.1+18.1 = 31.2 uF

V = 15 V

in parallel combination potential is constant

Q2 = V2*C2

Q2 = 15*18.1 = 271.5 uC

5)

C23 = 8+6 =14 uF

C123 = 12*14/26= 6.5 uF

6) C = 1.68 uF, V = 410 V

U = 0.5 CV^2

U = 0.5*1.68*10^-6*410^2

U = 0.14 J

7) E = 6*10^6 V/m

C = Aeo/d

A = Cd/eo

E = Q/Aeo

E = Q*eo/cdeo

E = Q/cd

6*10^6 = Q/(10^-10*0.001)

Q = 0.6 uC

correct option is (b)

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