Question

two point charges 8q and -2q are located at x=0 and x=L . the location of a point on the x axis at which the net electric field due to these two point charges is zero is
(a) 4L
(b)8L
(c)L/4
(d)2L

Answer 1

must be C

Answer 2

reason please ?

Answer 3

"on the x axis at which the net electric field due to these two point charges is zero "

Answer 4

even the others are on the x axis

Answer 5

Answer is a) 4L

Answer 6

yep @srivatsa1995

Answer 7

in which schul do u study @srivatsa1995

Answer 8

kv iisc

Answer 9

@shivam_bhalla how did u get 4L

Answer 10

Reason : Net field at the point must be zero

Assume r-->distance of the point where electric field is zero from origin.

Therefore

\[(k)(8q)/r^2 + k (-2q) / (r-2L)^2 = 0\]

therefore
\[(r/r-2L)^2=4\]

Therefore
\[(r/r-2L)=2\]

\[r = 2r-4L\]

Therefore

r=4L

Answer 11

why did u take r- 2l the whole square

Answer 12

E-field of 8q
=8q/(4 pi ε (x^2))

E-field of -2q
=-2q/(4 pi ε ((L-x)^2))

total E-field
=8q/(4 pi ε (x^2)) + -2q/(4 pi ε ((L-x)^2))

8q/(4 pi ε (x^2)) + -2q/(4 pi ε ((L-x)^2))=0
8(L^2 -2xL +x^2)-2x^2 =0
3x^2 -8xL +4L^2=0
(3x-2L)(x-2L)=0
x=2L