# Electromagnetism viva Questions and Answers

**• What is electromagnetism?**

Electromagnetism is a fascinating field of physics that studies the interactions between charged particles. It’s responsible for the electromagnetic force, one of the four fundamental forces in nature. This force is the reason why electrons are held in orbit around the nucleus, shaping the structure of atoms. Depending on the charges involved, the electromagnetic force can either attract or repel.

**• What is an electric field?**

An electric field is a vector field that represents the force experienced by a positive test charge placed at any point in space. It is defined as the force per unit charge.

**• What is a magnetic field?**

A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials.

**• What is Coulomb’s law? **

Coulomb’s law describes the force between two charged particles. It states that the force is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

\[ F = k \frac{|q_1 q_2|}{r^2} \]

\(F\) represents the force between the charges,

\(k\) is the Coulomb constant, approximately `8.99 x 10^9 N.m^2/C^2`

,

\(q_1\) and \(q_2\) are the magnitudes of the charges, and

\(r\) is the distance between the charges.

**• What is the difference between electric and magnetic fields?**

Electric fields originate from electric charges, or from time-varying magnetic fields. Magnetic fields originate from moving electric charges (currents) or from time-varying electric fields.

**• What is an electromagnetic wave?**

An electromagnetic wave is a wave that is generated by oscillating electric and magnetic fields. These fields oscillate in perpendicular planes to each other, and the direction of energy propagation is perpendicular to both fields.

**• What is the principle of electromagnetic induction?**

The principle of electromagnetic induction states that a change in the magnetic field within a closed loop of wire induces an electromotive force (EMF) in the wire. This is the fundamental principle behind many electrical devices such as transformers and electric generators.

**• How does a magnetic field interact with a moving charge?**

A moving charge in a magnetic field experiences a force perpendicular to both the direction of motion and the direction of the magnetic field.

This force is given by the equation \(F = qvB\sin(\theta)\),

where \(q\) is the charge,

\(v\) is the velocity,

\(B\) is the magnetic field strength,

and \(\theta\) is the angle between the velocity and the magnetic field.

**• What is Faraday’s law of electromagnetic induction?**

Faraday’s law of electromagnetic induction states that the electromotive force (EMF) induced in a circuit is directly proportional to the rate of change of magnetic flux through the circuit.

The law can be expressed as \(\epsilon = -\frac{d\Phi_B}{dt}\),

where \(\epsilon\) is the induced EMF,

\(\Phi_B\) is the magnetic flux,

and \(t\) is time.

**• What is the Biot-Savart law?**

The Biot-Savart law describes how currents produce magnetic fields. It states that the magnetic field \(d\vec{B}\) at a point due to a small current element \(Id\vec{l}\) is directly proportional to the current \(I\), the length of the current element \(d\vec{l}\), and the sine of the angle between \(d\vec{l}\) and the line joining the current element to the point, and inversely proportional to the square of the distance between the current element and the point.

The law is given by \(d\vec{B} = \frac{\mu_0}{4\pi}\frac{I d\vec{l} \times \hat{r}}{r^2}\),

where \(\mu_0\) is the permeability of free space,

\(\hat{r}\) is the unit vector pointing from the current element to the point,

and \(r\) is the distance from the current element to the point.

**• What is Ampere’s law?**

Ampere’s law relates the integrated magnetic field around a closed loop to the electric current passing through the loop. It states that the integral of the magnetic field \(\vec{B}\) around a closed loop is equal to \(\mu_0\) times the current \(I\) that passes through the loop. The law can be expressed as \(\oint \vec{B} \cdot d\vec{l} = \mu_0 I\), where \(d\vec{l}\) is an infinitesimal vector element of the closed loop.

**• What is the Lorentz force and how is it calculated? **

The Lorentz force is the force experienced by a charged particle moving in an electromagnetic field. It is the sum of the electric and magnetic forces on the particle, and is calculated using the equation \( \vec{F} = q(\vec{E} + \vec{v} \times \vec{B}) \),

where \(q\) is the charge of the particle,

\(\vec{E}\) is the electric field, \(\vec{v}\) is the velocity of the particle,

and \(\vec{B}\) is the magnetic field.

**• What is Gauss’s law in electromagnetism? **

Gauss’s law states that the total electric flux out of a closed surface is equal to the charge enclosed by the surface divided by the permittivity of free space. The law can be expressed as \( \oint \vec{E} \cdot d\vec{A} = \frac{Q}{\varepsilon_0} \),

where \(\vec{E}\) is the electric field,

\(d\vec{A}\) is an infinitesimal area element on the closed surface,

\(Q\) is the total charge enclosed by the surface,

and \(\varepsilon_0\) is the permittivity of free space.

**• What is the principle of superposition in electromagnetism?**

The principle of superposition states that the net electric field at a point due to a collection of charges is equal to the vector sum of the electric fields due to each individual charge. This principle is fundamental to many areas of physics, including electromagnetism.

**• How does the direction of the magnetic field produced by a current-carrying wire relate to the direction of the current? **

The direction of the magnetic field produced by a current-carrying wire can be determined using the right-hand rule. If you point your thumb in the direction of the current, your fingers will curl in the direction of the magnetic field.

**• What is the difference between a diamagnetic and a paramagnetic material? **

Diamagnetic materials are those that create an induced magnetic field in a direction opposite to an externally applied magnetic field, and are repelled by the applied magnetic field. On the other hand, paramagnetic materials create an induced magnetic field in the same direction as the applied magnetic field, and are attracted to the magnetic field.