Question

Three point charges 4q, Q and q are placed in a straight line of length l at points distant
0, l/2 and l respectively. The net force on charge q is zero. The value of Q is
a) q
b) 2q
c) - 1⁄2 q
d) 4 q

Answer 1

Answer:

Sorry don't know really

Answer 2

Given info : Three point charges 4q , Q and q are placed in straight line of length l at point distant 0, l/2 and l respectively.

To find : the net force on the charge q is zero. the value of Q is ...

solution : (0,0) 4q-----Q(l/2,0) ------q (l,0)

force exerted by 4q on the charge q , F₁ = k(4q)(q)/(l)² = 4kq²/l² ...(1)

force exerted by Q on the charge q, F₂ = kQq/(l/2)² = 4Qq/l² ...(2)

now, net force acting on the charge q = 0 [a/c to question]

⇒F₁ + F₂ = 0

⇒4kq²/l² + 4kQq/l² = 0

⇒Q = -q

Therefore the charge Q = -q. [ and magnitude or value of Q = q]