Question

$-10\mu c,40\mu C$ and q are the charges on three identical conductors P,Q and R respectively, Now P and Q attract each other with a force F when they are separated by a distance d. Now P and Q are made in contact with each other and then separated . Again Q and R are touched and they are separated by a distance 'd' . The repulsive force between Q and R is 4F . Then the charge q is:

• A. $10\mu C$
• B. $30\mu C$
• C. $40\mu C$
• D. $65\mu C$

Answer 1

The correct option is B $30\mu C$

$-10\mu C$ and $40\mu C$ and $q$ conductor $P,Q,R$.

distance $=d$

Now, $P$ and $Q$ are made in constant with each other and then separated. Again $Q$ and $R$ are to $Q$ and $R$ are to separated by distance $=d$

$F=\frac{10\times 40}{r^2}K$

or, $F=\frac{400}{r^2}K$

$F=\frac{400}{d^2}K$

$4F=\frac{40\times q}{d^2}\times K$

$4\times \frac{400K}{d^2}=\frac{40\times d}{d^2}\times K$

or, $q=\frac{400\times 4}{40}=40$

Now, $q=(40-10)C=30\mu C$