Question

The amount of work required to increase the distance between -6uC and 4uC from 6 cm to 18 cm will be:
(a) 1.8 J
(b) 2.4 J
(C) 1.8 uJ
(d) 2.4 uJ​

Answer 1

Answer:

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Explanation:

Answer 2

Given : Charge = -6μC , 4μC

            Initial distance = 6cm

            Final distance = 18cm

To find : work required to move increase the distance between two charges from 6cm to 18cm.

Solution :

Force = (k×q1×q2)/r²

          = (9×10^9 × |-6×10^-6| × |4×10^-6| )/ r²

          = (216 × 10^-3)/ r²

Now work required to increase the distance from 6cm to 18cm,

dW= F.dr

W = ∫F.dr

   = 216×10^-3∫1/r²dr

   =216×10^-3[-1/r]

   = 216×10^-3[ -1/18 - (-1/6)]

   =216×10^-3[2/18]

  = 24×10^-3

In joule work = 24× 10^-3 ×10^2

                      = 2.4 Joule

Therefore the option b is correct