The electric field just outside the surface of a conductor is directed how relative to the surface?

• A. Normal to the surface
• B. Tangential to the surface
• C. At 45 degrees to the surface
• D. Opposite to the normal

Answer: (A)

In electrostatics, the field just outside a conductor must be perpendicular to the surface. This comes from the fact that the field inside a conductor is zero, so any tangential component at the surface would push charges to move along the surface until that tangential part disappears. That leaves only a normal (perpendicular) component to the surface. The direction along that normal depends on the surface charge: it points away from the surface for positive charge and toward the surface for negative charge. Descriptions involving a tangential component or an oblique angle don’t occur in electrostatic equilibrium.