Please explain how at a surface of a charged conductor electrostatic field must be normal to the surface at every point

in electrostatic condition , 
1- the field inside the conducter is 0 . 
2- the field just outside the surface will be just normal to the surface , this is beacuse the surface of the conducter is an equipotential surface , as we move along any path in the surface , the dot product of field and displacement will be 0 . 

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