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Electric Charge – Definition, Formulae, Properties

In this article, we are going to learn about the definition of charge, its properties, some of the terms, formulae, and laws related to it, etc.

Table of Contents
  • What is a Charge?
  • Types of Electric Charges
  • How an Object gets Charged?
  • Unit of Charge
  • Properties of Electric Charge

What is a Charge?

Charge or Electric Charge is the basic property of any matter due to which it produces or experiences electro-magnetic effects.

An object that has an electric charge, it is said to be electrified or charged. When an object has no charge, it is said to be neutral.

Types of Electric Charges

There are basically two types of charges:

  • Positive Charge, e.g. charge of a proton
  • Negative Charge, e.g. charge of an electron

The terms positive charge and negative charge were coined by the American scientist Benjamin Franklin.

Note

Matter can have no charge at all, i.e. it may be neutral. It’s not essential for all matter to have either positive or negative charge.

This gives rise to two kinds of electrification effects.

  • Like charges repel each other – So, two positive charges repel each other. Also, two negative charges repel each other. For example, if you place two electrons together, they will move away from each other.
  • Unlike charges attract each other – So, a positive and negative charge will attract each other. For example, if you place an electron and a proton together, they will move towards each other.

When equal positive and negative charges meet, they neutralize each other.

How an Object gets Charged?

It was a mystery for a long time. Till Benjamin Franklin gave the concepts of positive and negative charges.

An object can get electrified in two ways:

  • It can get positively charged, either by gaining a positive charged particle, or by losing a negative charged particle.
  • It can get negatively charged, either by gaining a negative charged particle, or by losing a positive charged particle.

However, the most common way in which various objects get charged/electrified is by losing or gaining electrons.

As electrons are negative charges, a body that gains electrons gets negatively charged, and the body that loses electrons gets positively charged.

The number of electrons that an object needs to gain or lose to get charged are very small as compared to the total number of electrons in their body.

Static Electricity

Some of the loosely bound electrons of a matter can be transferred from it to another matter even just by rubbing.

Have you ever experienced the shock of Static Electricity. Sometimes, we receive a shock of static electricity just by touching some matter. Even a spark can be witnessed in some cases.

In around 600 BC Greece, Thales of Miletus rubbed amber with wool or silk cloth. He observed that amber had acquired some unique properties – it started to attract light-weight objects towards it. What he had basically done, was to charge or electrify amber by rubbing it. This is Static Electricity.

In fact, the term Electricity has come from a Greek word Elektron, which means amber.

Unit of Charge

Just like other properties of matter, we can measure charge in a matter too. For this purpose, we use a variety of units.

Coulomb

In the International System of Units (SI), a unit of charge is called a Coulomb. It is denoted by the symbol C.

However, Coulomb is a big unit. So, in electrostatics we often use a smaller unit of Micro Coulomb (μC) or Milli Coulomb (mC).

  • 1 μC = 10-6 C
  • 1 mC = 10-3 C

Basic Unit of Charge (e)

Charge on 1 electron or proton is considered the basic unit of charge.

  • The charge on one proton is denoted as +e
  • The charge on one electron is denoted as -e

Let’s find out its value.

To make a charge of -1 Coulomb we need 6 × 1018 electrons.
So, charge of 1 electron, i.e. e is 1.602192 × 10-19 C.

Same applies to protons.
To make a charge of 1 Coulomb we need 6 × 1018 protons (or we need to lose these many electrons).
So, charge of 1 proton, i.e. e is 1.602192 × 10-19 C.

In general, objects generally gain positive charge by losing their electrons, rather than by gaining protons. Some atoms can easily lose electrons. However, gaining or losing protons is not that simple a process.

Definition of Coulomb

It is the charge that flows through a wire if we run a current of 1 Ampere through it for 1 second.

Now, let’s have a look at some of the other basic properties related to charges.

Properties of Electric Charge

Charge is a Scalar Quantity

Charge is a scalar quantity, which means that it only has magnitude but no direction.

However, it is a bit different from some other matter properties like mass. Mass is also a scalar quantity, just like charge. Both have magnitude, but no direction. But mass cannot be negative. While charge can be positive or negative.

Note

You guys may have heard about Antimatter. When matter and antimatter come together mass is destroyed and pure energy is produced.

However, it does not mean that antimatter has negative mass. There’s nothing as negative mass, at least in the universe we live in. Mass is always positive.

Charges can add up or nullify each other

If a system contains multiple charges, then we can add them algebraically to find the total charge.

So, if there are n charges q1, q2, q3, …, qn in a system, then:
Total charge of the system = q1 + q2 + q3 + … + qn

Note

When we say that we need to add algebraically, we mean that we need to keep in mind the signs.

Quantization of Charge

All charges are integral multiples of the basic unit of charge, i.e. e.

So, total charge in a system (q) may be denoted as:
q = ne
Where n is any integer, positive or negative.

Note

The quantisation of charge was first suggested by Faraday. It was proved experimentally by Millikan in 1912.

Law of Conservation of Charges

If a system is isolated, then the total charges within it will remain the same. It will neither increase nor decrease. This is the law of Conservation of Charges.

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