What Is Electric Charge?

What Is Electric Charge?

Electrification of Bodies

When two bodies are rubbed together, they acquire the property of attracting light objects like small bits of paper, dust particles, etc. The bodies that acquire this property are said to be electrified or charged with electricity.

Charge

Charge is the basic property associated with matter, due to which it produces and experiences electrical and magnetic effects.

Types of Charges:

• Benjamin Franklin named the two types of charges positive and negative.

• Similar charges repel each other, and opposite charges attract each other.

Charging of Bodies: Charging of bodies takes place due to the transfer of electrons from one body to another.

List of Materials and Their Charging Behavior

The list below shows materials that will be positively charged when rubbed with any other material coming later in the list. The other material will naturally be negatively charged.

1. Fur

2. Flannel

3. Shellac

4. Sealing Wax

5. Glass

6. Paper

7. Silk

8. Human Body

9. Wood

10. Metals

11. India Rubber

12. Resin

13. Amber

14. Sulphur

15. Ebonite

16. Gutta Percha

Surface Density of Charge

Surface density of charge is defined as the amount of charge per unit area on the surface of a conductor.

• Dependence on Shape and Proximity: The surface density of charge at a point on the surface of a conductor depends on the shape of the conductor and the presence of other conductors or insulators near the given conductor.

• Radius of Curvature: The surface density of charge at any part of the conductor is inversely proportional to the radius of curvature of the surface of that part. This is why the surface density of charge is maximum at the pointed parts of the conductor.

Conductor

Conductors are those materials that allow electricity (charge) to pass through them. Good conductors have loosely bound electrons.

Examples of Conductors:

• Metals like silver, iron, and copper

• Earth (especially the moist part) acts as a huge conductor.

Best Conductor:

• Silver is the best conductor.

Insulator or Dielectric

Insulators are those materials that do not allow electricity to flow through them.

Examples of Insulators:

• Wood

• Paper

• Mica

• Glass

• Ebonite

Coulomb's Law

According to Coulomb's law, the force of attraction or repulsion between two point charges at rest is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them.

This force acts on the line joining the two charges.

Electric Field

The region in space around a charge or charged body where the charge has its electrical effect is called the electric field of the charge.

Electric Field Intensity

• The electric field intensity at a point in an electric field is the force experienced by a unit positive charge placed at that point.

Electric Field of a Hollow Conductor

• The electric field intensity inside a charged hollow conductor is zero.

• The charge given to such a conductor (or conductor of any shape) remains on its surface only.

• This explains why a hollow conductor acts as an electrostatic shield. It is for this reason that it is safer to sit in a car or bus during lightning.

Electric Potential

• The electric potential at a point in an electric field is the work done in bringing a unit positive charge from infinity to that point.

SI Unit: The SI unit of electric potential is the volt. It is a scalar quantity.

Potential Difference

• The work done in bringing a unit positive charge from one point to another point is the potential difference between the two points.

SI Unit: Its SI unit is the volt and is a scalar quantity.

Electric Capacity

• The electric capacity of a conductor is defined as the charge required to increase the potential of the conductor by unity.

• If the potential of a conductor is increased by V when a charge Q is given to it, the capacity of the conductor is C = Q/V.

SI Unit: The SI unit is farad (F).

Electrochemical Cell

An electrochemical cell is a device that converts chemical energy into electrical energy.

There are two types of cells:

• Primary Cell

• Secondary Cell

Primary Cell

In primary cells, electrical energy is obtained from the irreversible chemical reaction taking place inside the cell.

After complete discharge, the primary cell becomes unserviceable.

Examples of Primary Cells:

• Voltaic Cell

• Leclanché Cell

• Daniel Cell

• Dry Cell, etc.

Secondary Cell

• A secondary cell is one that has to be charged at first from an external electric source and then can be used to draw current.

• Such cells are rechargeable.

Discovery: The production of electricity by chemical reaction was first discovered by Alessandro Volta (the voltaic cell is named after him) in 1794.

Voltaic Cell

In a voltaic cell:

• A zinc rod is used as the cathode.

• A copper rod is used as the anode.

These rods are placed in sulfuric acid kept in a glass vessel.

Leclanché Cell

In a Leclanche cell:

• The carbon rod acts as the anode.

• The zinc rod acts as the cathode.

These rods are placed in ammonium chloride kept in a glass vessel.

The emf (electromotive force) of the Leclanche cell is 1.5 volts.

This cell is used for intermittent work, i.e., work in which continuous electrical energy is not required, such as an electric bell.

Dry Cell

• In a dry cell, a mixture of MnO₂, NH₄Cl, and carbon is kept in a zinc vessel.

• A carbon rod is placed in the mixture, which acts as the anode.

• The zinc vessel itself acts as a cathode.

• The emf of a dry cell is 1.5 volts.

Final Thoughts

Electric charge is a fundamental property of matter, existing in positive and negative forms.

According to Coulomb's Law, like charges repel and opposite charges attract. Charging occurs when electrons transfer between bodies, making one positively charged and the other negatively charged.

Materials can be conductors, like metals, that allow charge to flow, or insulators, like wood and glass, that prevent it. The surface density of charge is highest at the pointed parts of a conductor. Hollow conductors also shield their interiors from electric fields, making them useful for protecting sensitive equipment. These principles are key to understanding the behavior of electricity and electrical devices.