Physics · Electrostatic Potential And Capacitance · NEET
Both. Whether the conductor is neutral or charged, and whether or not there is an outside field, the static field inside is always zero. If you put a neutral conductor in an external field, its free electrons shift and induce charges on the surface. These induced charges create an opposing field inside that exactly cancels the external field. So the net field inside is zero in every case. This is why NCERT calls E = 0 inside a conductor the defining property of a conductor.
A conductor has free electrons that can travel large distances, so they keep moving until the internal field is fully cancelled (E = 0). A dielectric has no free electrons; its molecules only stretch or turn a little (polarisation). This induced field opposes the external field but does not fully cancel it, it only reduces it by a factor of the dielectric constant K. So conductor: field fully cancelled. Dielectric: field only weakened.
No, this is a common mix-up. Zero field means the potential does not change from point to point (E = -dV/dr, so if E = 0 then V is constant). The conductor is at one constant potential throughout its volume and surface. But that constant value is usually not zero. Zero field means constant potential, not zero potential.
Only in the static (final steady) situation. The moment charge is added or an external field is switched on, there is briefly a field inside and electrons rush to rearrange. This takes an extremely tiny time (about 10^-16 s for metals). After that rearrangement, the field is zero everywhere inside. NEET questions always mean this final static state.
Use Gauss's law. Take any tiny closed surface inside the conductor. Since E = 0 everywhere inside, the flux through it is zero, so the enclosed charge must be zero. This is true for every point inside. Therefore no net charge can sit in the interior, and all excess charge must reside on the outer surface.
Which of the following statements are correct? A. Inside a conductor, the electrostatic field is zero. B. Electric field at the surface of a charged conductor does not depend on its surface charge density. C. The interior of a charged conductor can have no excess charge in the static situation. D. At the surface of a charged conductor, the electrostatic field must be normal to the surface at every point. E. The electrostatic potential is zero everywhere inside a charged conductor.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Because a conductor has free electrons. If any field existed inside, these electrons would feel a force and keep moving. They rearrange onto the surface until the field they create cancels the outside field, making the net internal field zero in the static state.
No. It holds for neutral or charged conductors, with or without an external field. For a neutral conductor in an external field, induced surface charges cancel the field inside just the same.
Because the field inside a conductor (and inside a hollow cavity with no charge) is zero, the cavity is protected from outside electric fields. This is why sensitive instruments are placed inside metal enclosures. It is a direct use of E = 0 inside a conductor.
No. Zero field means the potential is constant everywhere inside and on the surface, but this constant value is usually not zero. Constant potential is not the same as zero potential.
All excess charge resides on the outer surface. Gauss's law shows that since E = 0 inside, no net charge can exist in the interior.
