Electric Charge - Definition, Properties, Formula, Types, Unit, FAQs

What is the Electric Charge?

In the class 12 Physics electric charge is the important topic and numerical questions and its types are often asked in the exams. Let's discuss the Electric charges and fields in detail.

Electric Charge Definition

Electric charge is a basic property of matter that causes it to experience a force when placed in an electric or magnetic field. It can be positive or negative, just like the charges on protons and electrons. Objects with the same type of charge repel each other, while those with opposite charges attract.

Students are confused whether Charge is a scalar and vector quantity. Answer to this question is that Charge is a scalar quantity.

S.I. Unit of Electric Charge

The SI unit of electric charge is the coulomb, represented by the symbol "C".

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Types of Charge:

There are two types of electric charges-positive and negative.

• Protons have a positive charge.
• Electrons have a negative charge.
• Neutrons have no charge and are neutral

Interaction of Charges

Like charges (Positive-Positive or Negative-Negative) repel each other (glass rods rubbed with wool or silk repel each other) and unlike charges ( Positive-Negative) attract each other (glass rod and wool attract each other).

Properties of charge:

1. Additivity: If a system contains n charge $q_1, q_2, q_3 \ldots \ldots q_n$, then the total charge of the system is $q_1+q_2+\ldots \ldots q_n$.

2. Conservation of Charge: The charge can be neither created nor destroyed. When we rub a glass rod with silk there is a transfer of charge and not creation. The total charge of an isolated system is always conserved.

3. Unit of Charge: The unit of electric charge is the coulomb (C).
   The charge of a single electron is approximately $-1.6 \times 10^{-19}$ coulombs.
   Similarly, a proton has a charge of $+1.6 \times 10^{-19}$ coulombs.

4. Quantization: The charge on a body will be some integral multiple of e, where e is the charge of the electron.
   $e=1.6 \times 10^{-19} \mathrm{C}$

Coloumb's Law

Force between two points charges is explained by the Coloumb's law.

Coloumb's law states that: "The magnitude of the electrostatic force (F) between two point charges is directly proportional to the product of the magnitudes of the charges and inversely proportional to the square of the distance between them."

it is represented by:

$
F=k \frac{\left|q_1 \cdot q_2\right|}{r^2}
$

where:

• $F$ is the magnitude of the electrostatic force between the charges,
• $q_1$ and $q_2$ are the magnitudes of the two charges,
• $r$ is the distance between the centers of the two charges,
• $k$ is the electrostatic constant, also known as Coulomb's constant, with a value of approximately $9 \times 10^9 \mathrm{Nm}^2 / \mathrm{C}^2$ in a vacuum.

Methods of Charging

• Charging by Friction – When two neutral objects are rubbed together, electrons are transferred from one object to another. For example, rubbing a balloon on hair makes it charged.
• Charging by Conduction – When a charged object touches a neutral object, electrons move from one to the other, and both objects get the same type of charge.
• Charging by Induction – In this method, a charged object is brought near (but not touching) a neutral object. The presence of the charged object causes a separation of charges in the neutral object.

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Solved Examples Based on Electric Charge

Example 1: Charge on $\alpha$-particle is:

1) $4.8 \times 10^{-19} \mathrm{C}$
2) $1.6 \times 10^{-19} \mathrm{C}$
3) $3.2 \times 10^{-19} \mathrm{C}$
4) $6.4 \times 10^{-19} \mathrm{C}$

Solution:

Electric charge

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

Alpha particles have a charge of +2 ,
Hence, the charge on an alpha particle is twice the electron charge

$
\begin{aligned}
& =2 \times 1.6 \times 10^{-19} \mathrm{C} \\
& \mathrm{q}=3.2 \times 10^{-19}
\end{aligned}
$

Hence, the answer is the option (3).

Example 2: Which of the following charges is not possible?
1) $1.6 \times 10^{-18} \mathrm{C}$
2) $1.6 \times 10^{-19} \mathrm{C}$
3) $1.6 \times 10^{-20} \mathrm{C}$
4) None of these

Solution:

$1.6 \times 10^{-20} \mathrm{C}$, because this is $\frac{1}{10}$ of electronic charge and hence not an integral multiple.

Hence, the answer is the option (3).

Example 3: When 10¹⁹ electrons are removed from a neutral metal plate, the electric charge on it is

1) $ -1.6 C$
2) $+1.6 C$
3) $10^{+19} \mathrm{C}$
4) $10^{-19} \mathrm{C}$

Solution:

Electric charge -The loss of electrons gives a positive charge.

By using

$Q=n e \Rightarrow Q=10^{19} \times 1.6 \times 10^{-19}=+1.6 C$

Hence, the answer is the option (2).

Example 4: When a body is earth-connected, electrons from the earth flow into the body. This means the body is

1) Unchanged

2) Charged positively

3) Charged negatively

4) An insulator

Solution:

When a positively charged body is connected to the earth, electrons flow from the earth to the body and the body becomes neutral.

Example 5: A conductor has $14.4 \times 10^{-19}$ coulombs positive charge. The conductor has (Charge on electron $=1.6 \times 10^{-19}$ coulombs )

1) 9 electrons in excess

2) 27 electrons in short

3) 27 electrons in excess

4) 9 electrons in short

Solution:

Electric charge

The loss of electrons gives a Positive charge

A positive charge shows the deficiency of electrons.

Number of electrons $=\frac{14.4 \times 10^{-19}}{1.6 \times 10^{-19}}=9$

Hence, the answer is the option (4).

Related Topics

• Electric Potential
• Electric Charge And Electrification
• Electric Dipole
• Equipotential Surface
• Kirchhoff first law