# Conductors

A conductor is a material that allows electric charges to move freely throughout its surface or volume. Some of the key properties of conductors are:

1. Any charges placed inside the conductor will distribute themselves uniformly on the surface of the conductor, causing the electric field within the conductor to become zero.
2. The excess charges on conductors will distribute themselves uniformly on the surface of the conductor, resulting in a high charge density at sharp points or edges.
3. When a charged object is brought near a conductor, the charges on the conductor's surface will redistribute themselves in response to the external electric field. This redistribution of charges will result in the creation of induced charges on the surface of the conductor.

## Conductors with Cavity

When a conductor with a cavity is placed in an electrostatic field, the charges on the surface of the conductor will redistribute themselves in response to the external electric field. This redistribution of charges will result in the creation of induced charges on the surface of the conductor, including the surface of the cavity. Some important features of conductors with cavities are:

1. When a conductor with a cavity is placed in an electrostatic field, the charges on the surface of the conductor will redistribute themselves, creating induced charges on the surface of the cavity.
2. The electric field within the cavity of a conductor with a cavity depends on the shape and size of the cavity and the surrounding material.
3. Conductors with cavities can act as electrostatic shields, preventing electric fields from penetrating the interior of the cavity.
4. The potential distribution within a conductor with a cavity depends on the location of any charges and the shape of the cavity. The potential inside the cavity can be different from the potential outside the cavity, which can lead to the generation of electric fields within the cavity.

## Problems from IIT JEE

Problems (IIT JEE 2007): Consider a neutral conducting sphere. A positive point charge is placed outside the sphere. The net charge on the sphere is then,

1. negative and distributed uniformly over the surface of the sphere.
2. negative and appears only at the point on the sphere closest to the point charge.
3. negative and distributed non-uniformly over the entire surface of the sphere.
4. zero.

Solution: The positive point charge induces negative charge in its vicinity but an equal amount of positive charge is induced in the remaining portion of the sphere. The net charge on the sphere remains zero.

Problems (IIT JEE 1996): A metallic solid sphere is placed in a uniform electric field. The lines of force follow the path(s) shown in the figure as

1. 1
2. 2
3. 3
4. 4

Solution: In electrostatics (i.e., when charges are not moving or the charge density does not vary with the time), electric field inside a conductor is zero. The field lines are normal to the surface and never enter inside a conductor.

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