 # Electrostatics Questions

The electric field is defined as the electric force per unit charge. The electric field is directed radially outward from a positive charge and inside towards a negative point charge. A static charge can generate only an electric field in the surrounding space. The electromagnetic field is a combination of both electric and magnetic fields. Stationary charges produce the electric field, and moving charges produce the magnetic field. These are the sources of the electromagnetic field.

Electrostatics is the branch of physics that deals with properties of charges at rest and slow-moving electric charges. When charged particles are transferred from one body to another, we can experience the existence of static electricity. One of the most common examples of the electrostatic force is sticking plastic wrap to one’s hand after it is removed from a package.

This concept arises from the forces applied by the electric charges and is explained by Coulomb’s law.

The formula gives coulomb’s Law of electrostatics:

The electric force on a charge Q1 under these conditions, due to a charge Q2 at a distance r, is given by Coulomb’s law:

$$\begin{array}{l}F=k\frac{q_{1}q_{2}}{d^{2}}\end{array}$$

Electric field (\vec{E})is a vector quantity defined as the electrostatic force \vec{E} in newtons on a hypothetical small test charge at the point due to Coulomb’s Law, divided by the magnitude of the charge q in coulombs

\vec{E}=\frac{\vec{F}}{q}

Electric field lines start on a positive charge and end on a negative charge. The density of electric field lines gives the amount (magnitude) of the electric field at any given point.

The smallest unit charge is 1.6021 x 10^-19 Coulomb (C). Neutral particles contain the same amount of electrons and protons.

Gauss’ law states that “In any closed surface of any shape placed in free space, the total electric flux in an electric field is proportional to the total electric charge enclosed by the surface”.

$$\begin{array}{l}\oint_{s}^{} \vec{E}.\vec{dA} = \frac{1}{\varepsilon_{0}}Q_{enclosed}=\int_{v}^{}\frac{\rho}{\varepsilon _{0}}.d^{3}r \end{array}$$

Gauss’s Law in differential form:

$$\begin{array}{l}\vec{\bigtriangledown} \vec{E} = \frac{\rho }{\varepsilon_{0}}\end{array}$$

### Poisson and Laplace equations

$$\begin{array}{l}{\bigtriangledown}^{2} \phi = -\frac{\rho}{\varepsilon_{0}}\end{array}$$

This relationship is a form of Poisson’s equation. When there is no unpaired electric charge, the equation becomes Laplace’s equation:

$$\begin{array}{l}{\bigtriangledown}^{2} \phi = 0\end{array}$$

Coulomb force is also called electrostatic force or Coulomb interaction. It is the force of attraction or repulsion of particles that arises due to the electric charges of particles. The force created by the electric field is much stronger than the force created by the magnetic field.

## Important Electrostatics Questions with Answers

1. Define electrostatics.

Electrostatics is the branch of physics that deals with phenomena and properties of stationary or slow-moving electric charges.

2. State Coulomb’s Law.

The force of attraction or repulsion between two charged bodies is directly proportional to the product of their charges and inversely proportional to the square of the distance between them.

3. What is the value of the electron (e) charge?

1. 1.60217662 × 10^-29
2. 1.60217662 × 10^-27
3. 1.60217662 × 10-9
4. 1.60217662 × 10-19

Explanation: The value of electron charge is 1.60217662 × 10^-19.

4. Neutral particles contain _____.

1. Equal numbers of protons and electrons
2. More protons than electrons
3. More electrons than protons
4. None of the options

Answer: a) Equal numbers of protons and electrons.

5. Which of the following is an example of electrostatics?

1. Shining of star
2. The attraction of paper to a charged scale
3. The explosion of grain silos
4. Option b) and c)

Answer: d) Option b) and c)

6. The electrostatic force is also known as the _____.

1. Charge force
2. Coulomb force
3. Electron force
4. None of the option

7. Coulomb’s law is given by the formula

1. $$\begin{array}{l}F=k\frac{q_{1}+q_{2}}{d^{2}}\end{array}$$
2. $$\begin{array}{l}F=k\frac{q_{1}-q_{2}}{d^{2}}\end{array}$$
3. $$\begin{array}{l}F=k\frac{q_{1}q_{2}}{d^{2}}\end{array}$$
4. $$\begin{array}{l}F=k\frac{2*q_{1}q_{2}}{d^{2}}\end{array}$$

8. Electric field is a _____.

1. Scalar quantity
2. Vector quantity
3. Dimensionless quantity
4. None of the options

Explanation: Electric field is a quantity that has both magnitude and direction.

9. In Coulomb’s law, ε is known as ____._

1. Relative permittivity
2. The permittivity of free space
3. Absolute permittivity
4. None of the option

Explanation: Absolute permittivity is a measure of the electric polarizability of a dielectric.

10. Define Static electricity.

Static electricity is an electrical event where charged particles are transferred from one body to another.

## Practice Questions

1. Explain Gauss Law in brief.
2. Give some examples to explain the electrostatic force.
3. List some properties of the electric field.
4. Give the formula of Coulomb’s law.
5. State true or false: Coulomb force is the attraction or repulsion of particles or objects because of their electric charge.

Watch the video below to understand electrostatics better. 