2) Find the potential energy associated with a pair of point-like electric charg

Question

2) Find the potential energy associated with a pair of point-like electric charges separated by a distance of 14.0 cm, assuming that the potential eneergy is zero when they are infinitely far apart. Let one charge be +80uC, and the other be -13uC.

3) Find identical capacitors are connected as shown below. the effective capacitance of the whole circuit, as viewed from the battery, is 15.0uF. What is the capacitance of each invidual capacitor?

* Do all these capacitors store the same amount of energy? If not, which have more energy?

Explanation / Answer

2.

Potential energy between the charges is given by

U=KQ1Q2/r

U=(9*109)(80*10-6)(-13*10-6)/0.14

U=-66.86 Joules

3.

Let the identical capacitor value be C ,equivalent capacitance

1/Ceq =1/(C+C+C) +1/C +1/C

Ceq=0.42857C

given Ceq=15 uF

15=0.42857C

C=35 uF

b)

No all capacitors wont store same amount energy

Let three capacitors in parallel be C3,C4 and C5 and remaining capacitors be C1 and C2

Total charge

Q=CeqV =15V uC

Q1=Q2=15V uC

Q3=Q4=Q5=15V/3 =5V uC

energy stored in capacitor is given by

U=Q2/2C

Therefore C1 and C2 will have more energy

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