Inducing a Positive
Charge on a Sphere
A GIF Animation
There are a variety of ways to charge an object. One such way is
known as induction. In the induction process, a charged object is
brought near but not touched to a neutral conducting object. The
presence of a charged object near a neutral conductor will force (or
induce) electrons within the conductor to move. The movement of
electrons leaves an unbalance of charge on opposite sides of the
neutral conductor. While the overall the object is neutral (i.e., has
the same number of electrons as protons), there is an excess of
positive charge on one side of the object and an excess of negative
charge on the opposite side of the object. Once the charge has been
separated within the object, a "ground" is brought near and touched
to one of the sides. The touching of the ground to the object permits
a flow of electrons between the object and the ground. The flow of
electrons results in a permanent charge being left upon the object.
When an object is charged by induction, the charge received by the
object is opposite the charge of the object which was used to charge
it.
The animation below depicts the induction process. A neutral
conducting sphere is at rest on top of an insulating stand. A
negatively-charged tube is brought near to (without touching) the
neutral sphere. The presence of the negatively-charged tube forces
electron movement from the left to the right side of the sphere. This
movement of electrons is merely a reaction to the presence of
negative charge (like charges repel). Once touched by the ground, the
electrons leave the sphere. When the tube is moved away, there is an
overal positive charge left on the sphere.
During the induction process, there is never any movement of
electrons from the charged object to the sphere. The charged object
is only used to induce electron movement. Electrons, being negatively
charged, move about the conducting sphere as they are repelled by the
negatively-charged tube. Once the ground is touched to the sphere,
the electrons can even move further from the negatively-charged tube
by leaving the sphere and moving through the ground. It is at
this point that the sphere acquires an unbalance of charge. Since
there was a loss of negative charge in the form of electrons, the
overall charge on the sphere is positive.
The induction process is characterized by the following general
features:
- A charged object is needed to charge an object by
induction. Yet there is never any contact made between the charged
object and the object being charged.
- Only conductors can be charged by the induction process.
The process relies on the fact that a charged object can force or
induce the movement of electrons about the material being
charged.
- The object being charged ends up with a charge which is the
opposite of the object being used to charge it.
- A ground must be used to create the charge on the object.
The ground allows for electron movement into or out of the object
being charged.
Additional information on physical descriptions of optical
systems will soon be available at
The
Physics Classroom.
This page was created by
Tom
Henderson of
Glenbrook South
High School.
Comments and suggestions can be sent by e-mail to
Tom
Henderson.
This page last updated on 2/9/98.