# two point charges +36 and -16 microcoulumb are placed 10 cm apart. at a point x, there is no resultant force on positive charge. the distance of x from +36 microcoulumb charge is

Chetan Mandayam Nayakar
312 Points
12 years ago

if there is no resultant force, it implies that forces due to the charges are equal and opposite. this can happen only on the line connecting the two charges. this cannot happen between the two charges for obvious reasons. larger charge exerts greater magnitude force,because of which resultant force on positive charge is zero only on the line connecting two charges such that the zero force point and the -16 microcoulomb charge lie on the same side of the +36 microcoulomb charge

(1/4pik)(36/(x^2))=(1/4pik)(16/(x-10)^2)), ((x-10)^2)/16 =(x^2)/36,((x-10)^2)/4= (x^2)/9

(x-10)/2 =±x/3,3x-30=±2x, x=30 or 6, x>10, therefore x=30 cm

12 years ago

Hello Eshita !

Good morning :)

Well this is very easy question ...try to understand the steps of solving ...

First of all given that distance between the two charge is 10 cm ..

And if you will place the charge between the two charges ...then it will always experience a force..I mean to say that between the two charges there can't be any point where force is zero .. Understand by figure

So the only options is to put the charge either side of the two charges . okay ..

Cosider this figure ..

Then net force on the charge is ...

K 36/ (10+x)^2  - ( K 16/ (x)^2 ) = 0   ( because we have to find x for which net force is zero) ..

36(x)^2 = 16(10+x)^2

6x = 40 + 4x

x = 20 cm ..

Hence from 36 columb charge distance is ...10+20 = 30 cm ...Refer the figure ...

Regards

Yagya