The angle between the electric lines of force and the equipotential surface is:

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Accepted Answer

1. **Definition:** An equipotential surface is a region where the electric potential ($V$) is constant at every point. Therefore, the potential difference ($dV$) between any two points on the surface is zero.
2. **Work Done:** The work done to move a charge $q$ on an equipotential surface is $dW = q dV = 0$.
3. **Relation to Field:** Work is also defined as the dot product of force and displacement: $dW = \mathbf{F} \cdot d\mathbf{r} = q \mathbf{E} \cdot d\mathbf{r} = q E dr \cos 	heta$, where $	heta$ is the angle between the electric field ($\mathbf{E}$) and the displacement ($d\mathbf{r}$) along the surface.
4. **Conclusion:** For $dW$ to be zero (where $q, E, dr 
eq 0$), $\cos 	heta$ must be zero. This implies $	heta = 90^\circ$. Thus, electric field lines are always perpendicular to equipotential surfaces.

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