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  • Stuck here, help me understand: - Electrostatics - JEE Main

Three charges 4q,Q and  q  are in a straight line in the position of 0, l/2 and l respectively. The resultant force on q will be zero, if  Q=

  • Option 1)

    -q\; \;

  • Option 2)

    \; -2q\;

  • Option 3)

    \; -\frac{q}{2}\;

  • Option 4)

    \; 4q

 

Answers (1)

best_answer

As we learned

Coulombic force -

F\propto Q_{1}Q_{2}=F\propto \frac{Q_{1}Q_{2}}{r^{2}}=F=\frac{KQ_{1}Q_{2}}{r^{2}}

- wherein

K - proportionality Constant 

Q1 and Q2 are two Point charge

 

 The force between 4q and q ;  F_{1}=\frac{1}{4\pi \varepsilon _{0}}.\frac{4q\times q}{l^{2}}

The force between Q and q ;  F_{2}=\frac{1}{4\pi \varepsilon _{0}}.\frac{Q\times q}{(l/2)^{2}}

We want   F_{1}+F_{2}=0\; or\; \frac{4q^{2}}{l^{2}}=-\frac{4Qq}{l^{2}}\Rightarrow Q=-q

 


Option 1)

-q\; \;

Option 2)

\; -2q\;

Option 3)

\; -\frac{q}{2}\;

Option 4)

\; 4q

Posted by

Plabita

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