Methods of charging: Friction, Conduction, Induction, Examples and FAQ’s

Methods of Charging: We touch various objects throughout the day but somedays we feel a slight electric shock while touching surfaces like metallic handles or switches. In fact, in winters, sparks can be seen while donning or removing woollen clothes. These sparks are nothing but a discharge of electric charge. In general, we are surrounded by neutral objects.

A neutral body is one that contains an equal number of electrons and protons. At times this balance between the magnitude of these charges within a body gets disturbed and a neutral body becomes charged. Depending on the amount of charge on its surface, touching such a charged body can give us a slight shock. There are various methods by which we can charge an object. Let us learn about them in detail.

Learn About Charging by Friction

What is Charging?

All bodies, in general, are electrically neutral. All bodies are made of atoms, and a neutral atom as a whole consists of an equal number of positive and negative charges. The positively charged particles are called protons, while the negatively charged particles are called electrons. If the number of electrons and protons in an atom is not balanced, the body will possess an electric charge. If the number of protons is greater than the number of electrons, the body is positively charged. If the number of electrons exceeds the number of protons, the body is negatively charged.

An uncharged body becomes charged by gaining or losing electrons, and this process is called charging.
We can use the following three methods to charge an uncharged body:
1. Charging by friction
2. Charging by conduction
3. Charging by induction

Charging by Friction

The oldest known method of charging is charging by friction. Friction comes into play when two objects in contact are moved across each other. When two objects are rubbed against each other, the electrons from one object get transferred from one object to another. The rubbing of two surfaces involves friction. Thus, the transfer of electrons between two objects takes place due to friction. The object that loses electrons gains a positive charge, becoming positively charged.

The object that gains electrons gets a negative charge, becoming negatively charged. The charge lost by the positively charged object is equal to the charge gained by the negatively charged body; in other words, the charge always remains conserved. Thus, the objects become charged. The charge gained by the objects is called the friction charge. This method of charging is also called electrification by friction.

Examples of charging by friction: When a glass rod is rubbed with a silk cloth, the glass rod loses electrons and becomes positively charged, and silk cloth gains electrons and becomes negatively charged.

When an ebonite rod is rubbed with wool, negative charges move from the piece of wool to the ebonite rod. Thus, the piece of wool becomes positively charged while the ebonite rod becomes negatively charged.

Charging by Conduction

A neutral body has an equal number of electrons and protons, while a charged body contains an unequal number of positive and negative charges. When a charged body is brought in contact with an uncharged conductor, the charges are transferred from the charged body into the conductor. This method of charging is known as charging by conduction.

Consider the following example: A metallic uncharged rod \(A\) is kept on an insulated plastic stand when a negatively charged rod \(B\) is brought close to it. When rod \(B\) touches rod \(A\), the negative charges flow from the metal rod \(B\) into rod \(A\). Thus the uncharged rod \(A\) gains electrons and becomes negatively charged. In charging by conduction:

1. Both the charged and uncharged conductors possess the same type of charge.
2. Since the total charge remains conserved, when the two surfaces are brought in contact, charges get distributed over the two surfaces. Thus, when two same objects are brought in contact, the total charge gets equally distributed over the two objects.
3. When two similar bodies with the same magnitude of opposite charges are brought in contact, they become electrically neutral.
4. When two spheres are brought in contact, the charges are distributed over them proportional to their radius. When two spheres of radius \(r_1\) and \(r_2\) having charges \(q_1\) and \(q_2\) are brought in contact,
   \({q_{{\text{net}}}} = \frac{{{q_1} + {q_2}}}{{{r_1} + {r_2}}}\)
   Charge on each sphere after contact,
   Charge on the first sphere,
   \({q_1} = \frac{{{q_1} + {q_2}}}{{{r_1} + {r_2}}} \times {r_1}\)
   Charge on the second sphere,
   \({q_2} = \frac{{{q_1} + {q_2}}}{{{r_1} + {r_2}}} \times {r_2}\).

Charging by Induction

The method of charging in which an uncharged body is charged by bringing a charged body close to it is known as charging by induction. Both the bodies are brought close enough yet not in physical contact. When brought close to an uncharged body, the charged body induces a charge over it such that the polarity of the charges on the two bodies is opposite. An example of charging by induction – When a ruler is rubbed several times on the hair, it gets charged. When it is brought close to small pieces of paper, it attracts the bits by charging due to induction.

Lets us how understanding how charging by induction takes place. Consider two metal spheres \(A\) and \(B\), as shown in the figure given below:

Now a negatively charged balloon is brought close to the metal sphere \(A\). The negatively charged balloon will repel the electrons within the two spheres. Thus, the electrons within the two spheres will shift away from the negatively charged balloon. Therefore, the electrons from sphere \(A\) move towards sphere \(B\). Due to this transfer of electrons from sphere \(A\) to \(B\), sphere \(B\) becomes negatively charged. Due to the loss of electrons, sphere \(A\) becomes positively charged so that the overall two-sphere system remains electrically neutral. The two spheres are then separated using an insulated medium like the plastic stand or gloves.

When the spheres are separated by a reasonable distance and the charged balloon is removed, the charges on the two spheres get redistributed. The charge on each sphere spreads uniformly so that sphere \(A\) becomes positively charged while sphere \(B\) becomes negatively charged.

If instead of a negatively charged balloon, a positively charged balloon is brought close to the system of the two uncharged spheres, then sphere \(A\) will become negatively charged. At the same time, sphere \(B\) will become positively charged.

Gold Leaf Electroscope

A gold-leaf electroscope is a device that is used to detect the presence of an electric charge on a body. It is based on the principle of charging by induction. According to the principle of electrostatic induction, when a charged body \(A\) is brought close to an uncharged body \(B\), a charge of opposite polarity gets induced on the uncharged body \(B\).

A gold-leaf electroscope consists of a vertical metal rod fitted in an insulated container like a glass vessel, with a suitable rubber cork fitted in the mouth of that vessel. Two thin leaves of equal size are attached to the lower end of this metal rod. When a charged object is brought close to the metal knob attached at the top of the metal rod, a charge gets induced on the metal rod. The charge from the metal knob travels through the rod into the leaves. Since both the leaves acquire the same charge, a force of repulsion acts between the leaves, due to which the leaves diverge. The degree of divergence of the leaves gives an idea regarding the amount of charge flowing through the rod.

Thus, using a gold leaf electroscope, we can detect the presence of a charge, the polarity of charge, and the magnitude of the charge on a given charged body.

Summary

An uncharged body becomes charged by gaining or losing electrons, and this process is called charging. We can use the following three methods to charge an uncharged body:

1. Charging by friction
2. Charging by conduction
3. Charging by induction

A gold-leaf electroscope is a device that is used to detect the presence of an electric charge on a body. It is based on the principle of charging by induction.

Learn Basic Properties of Electric Charge

Frequently Asked Questions

Q.1. If a negatively charged metallic rod is brought in contact with an uncharged metal sphere. What type of charge will be produced on the metal sphere?
Ans: The metal sphere will gain a negative charge.

Q.2. What is charging by induction?
Ans: The method of charging by which an uncharged body gets charged when a charged body is brought close to it is known as charging by induction.

Q.3. What type of charge is produced on an ebonite rod when it is rubbed with wool?
Ans: The ebonite rod becomes negatively charged.

Q.4. Which device is used to detect the presence of charge?
Ans: An electroscope is used to detect the presence of a charge.

Q.5. How does a gold-leaf electroscope give an idea about the magnitude of the charge on a body?
Ans: The greater the divergence of leaves, the greater the charge on the body and vice versa.

Now you are provided with all the necessary information on the methods of charging and we hope this detailed article is helpful to you. If you have any queries regarding this article, please ping us through the comment section below and we will get back to you as soon as possible.