Question

The point charges Q and -2Q are placed at some distance apart. If the electric field at the location of Q is E. The electric field at the location of -2Q will be :

• A. $-\frac{3E}{2}$
• B. $-E$
• C. $-\frac{E}{2}$
• D. $-2E$

Answer 1

The correct option is C $-\frac{E}{2}$

As field at Q is E so force on Q is $F=QE$

Let the field at -2Q is $E^{\prime }$. So force on -2Q is $F^{\prime }=-2Q{E}^{\prime }$

According to Coulomb's law , the forces on both will be equal. so $F=F^{\prime }$ or $QE=-2Q{E}^{\prime }$ or $E^{\prime }=-E/2$