Question

Describe and diagram the processes of charging by induction and conduction (contact). Be sure to point out how the processes are similar and different, especially with reference to charges.

Answer 1

CHARGING BY CONDUCTION:

BASIC DEFINITION:

Charging by conduction involves the contact of a charged particle to a neutral particle. When an uncharged object is brought to a charged conductor, then there occurs the sharing of charge between the two conductors and hence the uncharged conductor gets charged.

We know that a current through a conductor flows when a difference in potential exists between its two ends. As due to the difference in potential, the electric field exists across the conductor. This electric field applies electrostatic force on the charges, due to which charges move and the movement of charges generates an electric current.

During charging by conduction, both the conductors acquire the same charge.

CHARGING BY INDUCTION:

BASIC DEFINITION:

When 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 induce (force) electrons within the conductor to move. The movement of electrons leaves an imbalance of charge on opposite sides of the neutral conductor. While the overall 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.

As we have already discussed that current in any conductor flows due to the movement of charge carriers.

Suppose we have a negatively charged body, so the movement of the charges inside the body generates an electric current. We know that when current flows through a conductor then the magnetic field is produced across it.

And according to Faraday when an uncharged body is placed in a region where the magnetic field is present then the electric field gets generated inside it.

  

More simply we can say charges of opposite polarity present in the charged body get induced to the uncharged body. Thus the generated electric field in the second body causes the flow of current through it in the opposite direction.

The magnetic field shows variation according to the change in the electric field of initially charged conductor and so the induced electric field in the other body.

So we can say that current flowing to one conductor gets induced in the other conductor placed near to it.

CHARGING BY INDUCTION USING A POSITIVE CHARGE:

Let us take a negatively charged rubber balloon. If we bring the charged balloon near the spheres, electrons within the two-sphere system will be induced to move away from the balloon due to the repulsion between the electrons of the balloon and the spheres. Subsequently, the electrons from sphere A get transferred to sphere B.The migration of electrons causes the sphere A to become positively charged and the sphere B to be negatively charged. The overall two-sphere system is hence electrically neutral. The spheres are then separated using an insulating cover such as gloves or a stand as shown in the figure (avoiding direct contact with the metal). When we remove the balloon, the charge gets redistributed, spreading throughout the spheres, as shown in the figure.

When a negatively charged balloon is brought near the sphere system, the electrons in the sphere will be forced to move away due to repulsion. The migration of electrons causes sphere A to become completely positive and sphere B to become negative.

CHARGING BY INDUCTION USING A POSITIVE CHARGE:

Take two spheres A and B, touching each other, as shown in the figure, if we bring a positively charged balloon near sphere A, the electrons from sphere B migrate towards sphere A due to the attraction between opposite charges, thus leaving the sphere B deficit of electrons. As a result, the sphere A is negatively charged and the sphere B is positively charged. The spheres are then separated using an insulating cover, a stand or gloves. When the balloon is removed, the charges in sphere A and B redistribute, spreading out evenly.

When a positively charged balloon is brought near the sphere system, the electrons from sphere B will migrate towards sphere A due to the force of attraction. Now, sphere A is negatively charged and the sphere B is positively charged.

SIMILARITIES BETWEEN CHARGING BY CONDUCTION AND INDUCTION:

Both conduction and induction involve a movement of electrons. Conduction is the transfer of electrons from a charged object to another object by direct contact. Induction does not involve direct contact. Instead, induction is the movement of electrons from one part of an object to another as a result of the electric field of the second object.

DIFFERENCE BETWEEN CHARGING BY CONDUCTION AND INDUCTION:

Basis for Comparison	Conduction	Induction
Basic	It results in a flow of current due to the electric field.	It results in a flow of current due to change in the magnetic field.
Arrangement of conductors	It requires direct contact between charged and uncharged conductors.	No direct contact is required between charged and uncharged bodies.
Direction of current	The current in both the conductors flows in the same direction.	The induced current is opposite in direction as that of actual current.
Gradient path	Due to transferring nature of charges, the gradient path is required.	Due to inducing nature of charges, the gradient path is not required.
Amount of charge	Decreases, due to distribution of charges.	Remains constant

The differences between the two methods of charging a body are as follows:

a) Charging a body by conduction is done by touching a charged body, whereas no touching is needed to charge a body by induction.

b) In charging by conduction, charge moves from charged body to uncharged body, whereas in charging by induction no charge flows from charged body to the uncharged body.

c) Some charge is lost in charging by conduction, whereas there is no loss in any charge in charging by induction.