There are 3 charges+ 1muC, -3muC and -3muC. They are placed at comers of an equi

Question

There are 3 charges+ 1muC, -3muC and -3muC. They are placed at comers of an equilateral triangle given in the diagram below. Calculate the magnitude and direction of the force on the +1muC charge. There are 2 charges, each 2 C, which are 0.4 m apart, calculate the repulsive force. Some glass rod can carry a charge of +0.24muC after being rubbed with a silk cloth. How many electrons were removed from this rod? Consider two point charges +2mutC and -3muC that is 0.4 m apart. (a) Calculate the electrostatic force at the point midway between them, and then (b) calculate the electrostatic force at some point 0.3 m from each charge.

Explanation / Answer

1) let q1 = +1 micro C

q2 = q3 = - 3 micro C

F21 = F31 = k*q1*q2/r^2

= 9*10^9*1*10^-6*3*10^-6/0.5^2

= 0.108 N

angle between F21 and F31 is 60 degrees

so, Fnet = sqrt(F21^2 + F31^2 + 2*F21*F31*cos(60))

here, F21 = F31

so, Fnet = sqrt(3)*F21

= sqrt(3)*0.108

= 0.187 N (downward)

2)
F = k*q^2/r^2

= 9*10^9*2^2/0.4^2

= 2.25*10^11 N

3) Q = n*e

n = Q/e

= 0.24*10^-6/1.6*10^-19

= 1.5*10^12 electrons

4) E = k*q1/r1^2 + k*q2/r2^2

= 9*10^9*2*10^-6/0.2^2 + 9*10^9*3*10^-6/0.2^2

= 1.125*10^6 N/c ( towards -3 micro C)

b) at a point close to + 2 micro C

E = k*q1/r1^2 - k*q2/r2^2

= 9*10^9*2*10^-6/0.3^2 - 9*10^9*3*10^-6/(0.4+0.2)^2

= 1.25*10^5 N/c ( away from +2 micro C)

at a point close to - 3 micro C

E = k*q2/r2^2 - k*q1/r1^2

= 9*10^9*3*10^-6/0.3^2 - 9*10^9*2*10^-6/(0.4+0.2)^2

= 2.5*10^5 N/c ( towards - 3 micro C)

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