Electrical Charges and its Properties

Electrical Charges (q)

Electrical charges are the intrinsic property of the elementary particles of matter which give rise to an electric force between various objects.It is a scalar quantity.

Minimum possible charge is $\pm\ 1.6 \times 10^{-19} C$

Electrical Charges on an,

  • Electron is $-\ 1.6 \times 10^{-19} C$
  • Proton is $+\ 1.6 \times 10^{-19} C$
  •  $\alpha\ – $ particle is $+ 2e$

Electric charges can be positive or negative and the property which differentiates these two kinds of charges is called the ‘Polarity of charge.

Positive Charge means the shortage of electrons while Negative charge means an excess of electrons.

If there are two bodies of equal mass. If we give a positive charge to the first body and same amount of negative charge to the second body. Then, the mass of the second body will increase as the number of electrons increases.

Like charges repel each other and the unlike charges repel each other.

SI unit of electrical Charges is coulomb (C). CGS unit of electrical charges statcoulomb (stat C) and the dimensional formula of charge is [q] = [AT].

\[\text{1 columb}= 3\times10^9 \text{esu} = \frac{1}{10}\text{ emu}\]

\[\text{1 columb}= 6.25 \times 10^{18} \text{electons} \]

The charged particle at rest, produces an electrical field.

Under the accelerated and unaccelerated motion, charged particle produces both Electrical field and Magnetic field.

If we observe with reference to release of energy, the accelerated charged particle radiate energy while the charged particle under unaccelerated motion doesn’t radiate energy.

Properties of electrical charges

Addivity of charge – This means the charges are added similar to the real numbers. while adding electrical charges, their signs$(\pm)$ must be taken into account.

\[q_{\ \text{net}}=q_{1}+q_{2}\]


Sum of $+2q$ and $+q$ is $+3q$ whereas the sum of $+2q$ and $-q$ is $+q$ only.

Charged is conserved – Charge carried by an isolated system is neither be created nor destroyed. It can only be transferred from one body to another body.

i.e. Charges can be created or destroyed only in equal and opposite pairs.

Quantisation of charge – The charge on anybody can be expressed as the integral multiple of the basic unit of charge.any free particle has no charge at all or a charge of $+15\ e^{-}$ or $-10\ e^{-}$ but not a free particle with a charge, say $5.89\ e^{-}$

\[q=\pm\ ne\]

Where, n = 1, 2, 3, 4, …

Unit used – $q$ and $e$ are in columb, $n$ is a number having no units.

Concept: 1  Calculation of remaining charge on the body.

When electrons are removed from a neutral body and to calculate remaining charge on the body

\[\text{Charge on the body} = \text{Number of electrons removed} \times 1.6 \times 10^{-19} C\]

Concept: 2 Calculaton of electrons when +ve or -ve charge on the body is given.

  • To calculate the number of the electron on a body, when the positive charge on the body is given.

\[\text{Number of electron} = \frac{\text{Positive charge on the body}}{1.6 \times 10^{-19} C}\]

  • To calculate the number of the electron on a body, when the negative charge on the body is given.

\[\text{Number of electron} = \frac{\text{Negative charge on the body}}{1.6 \times 10^{-19} C}\]

Conductor and Insulators

Conductors are the substances through which electrical charges can easily flow. e.g. Metals, graphite etc.

Insulators are the substances through which electrical charges cannot flow easily. e.g. Plastic, wood etc.

Methods of charging

Actually charging occur due to the actual transfer of electrons from one material to another. The insulating material becomes positively charge because of lower work function and vice-versa

The main methods of charging of a body are: charging by rubbing, charging by contact, and charging by induction.

Charging by rubbing

When two bodies are rubbing to each other, some electrons pass from one body to other. The electron donating body become positively charge while the body which receives electrons become negatively charged

For Example,

  1. Rubbing a glass rod with silk cloth,
    • Glass rod loses electrons and becomes negatively charged.
    • Silk cloth receives electrons and becomes Positively charged.
  2. On rubbing ebonite with wool,
    • Ebonite becomes negatively charged by receiving electrons.
    • Wool acquires positively charged by losing electrons.
  3. When a comb runs through one’s dry hairs the atoms in the paper get polarised by the charged comb. Due to this, it attracts small bits of papers.

Charging by contact or conduction

Two conductors, one charged and other uncharged are brought in contact with each other. The -ve or +ve charge spread over both conductors. Thus, both conductors will be charged with the same sign.

When a body is connected to earth, then electrons flow from earth to the body till it becomes neutral. when the connected body is negatively charged the electrons flow from the body to the earth till its get neutralized.

Charging by induction

In this process, the charging is done without actual contact of bodies. If a charged body is brought near an uncharged body, the near side of the uncharged body becomes oppositely charged while another side becomes similarly charged as the charged body.

Difference between Electrical Charges and Mass

  • Electrical charges can be positive, negative or zero while the mass of a body is a positive quantity.
  • The charge of a body doesn’t depend upon the velocity of the body but the mass of a body increases with its velocity.
  • Electrical charges are always conserved but mass can be changed into energy and vice-versa. Thus, the mass of a body is not conserved.
  • The force between charges can be attractive or repulsive depends upon the nature of charges. The gravitational force between two mass is always attractive.

Read – Concentration calculation in solutions