Question

two point charges Q and 4Q are seperated by a distance x. A neutral point is found at a distance r from the weaker charge in between the charges. express r in terms of x
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Answer 1

Answer:

Correct options are A) , B) and C)

Let r be the distance on the right of −Q/4 where potential is zero. so,

kQ/(r+x)−kQ/4r=0⇒4r−r−x=0⇒r=x/3

When r be the distance on the left of −Q/4,

kQ/(x−r)−kQ/4r=0⇒4r−x+r=0⇒r=x/5

Let electric field is zero at a distance r on the right side of the charge Q/4, so

kQ/(r+x)

2

−kQ/4r

2

=0⇒4r

2

−(r+x)

2

=0⇒(2r+r+x)(2r−r−x)=0

∴2r+r+x=0⇒r=−x/3

2r−r−x=0⇒r=x