Electrostatics Question 511
Question: Charges 4Q, q and Q and placed along x-axis at positions $ x=0,x=l/2 $ and $ x=l $ , respectively. Find the value of q so that force on charge Q is zero [DPMT 2005]
Options:
A) Q
B) Q / 2
C) -q / 2
D) -q
Show Answer
Answer:
Correct Answer: D
Solution:
The total force on Q $ \frac{Qq}{4\pi {\varepsilon _{0}}{{( \frac{l}{2} )}^{2}}}+\frac{4Q^{2}}{4\pi {\varepsilon _{0}}l^{2}}=0 $
$ \frac{Qq}{4\pi {\varepsilon _{0}}{{( \frac{l}{4} )}^{2}}}=-\frac{4Q^{2}}{4\pi {\varepsilon _{0}}l^{2}}\Rightarrow q=-Q. $
