Moving Charges and Magnetism: Important Questions

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Namrata Das

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The flow of charge or moving charges induce magnetism. Magnetism and moving charges illustrate magnetic fields exercise forces on the flow of charge, which deploys a force on other magnets. This phenomenon occurs because of the existence of constant moving charges. Here in this article, we will discuss some important questions on the topic “moving charges and magnetism”. 

Moving Charges and Magnetism
Moving Charges and Magnetism

Also check: Semiconductor Diode


Very Short Answer [1 Marks Questions]

Ques. What is an electric current?

Ans. An electric current is a flow of electric charge that takes place through a conductor.

Ques. What is an electromagnet?

Ans. An electromagnet is a magnet made from a coil of wire that carries an electric current. The magnetic field created by the current in the wire can be used to pick up metal objects.

Ques. Does the charge provided to a metallic sphere rely on whether it is solid or hollow? Give explanation.

Ans. An electric current will flow through a metal sphere, whether it is solid or hollow. The charge on the outside of the sphere will be equal to the charge on the inside.

Ques. How is the strength of an electromagnet controlled?

Ans. The strength of an electromagnet is controlled by the amount of electric current that flows through it.

Ques. What is an electric field?

Ans. An electric field is a region of space around a charged object where the force of electric attraction or repulsion can be felt.

Ques. How is the direction of an electric field determined?

Ans. The direction of an electric field is determined by the direction of the force it exerts on a charged object.

Ques. What is electric potential?

Ans. An electric potential is the amount of work that needs to be done to move a unit of electric charge from one point in an electric field to another point.

Ques. How is the electric potential at a point in space determined?

Ans. The electric potential at a point in space is determined by the amount of charge at that point and the strength of the electric field.

Ques. What is an equipotential surface?

Ans. An equipotential surface is a surface where the electric potential is the same at all points.

Also check: Potential Energy


Short Answer Questions [2 Marks Questions]

Ques. What is an electric potential difference?

Ans. An electric potential difference is a difference in electric potential between two points. It is measured in volts.

Ques. What is an electric field line?

Ans. An electric field line is a visual representation of the electric field at a point in space. It shows the direction of the force that the electric field exerts on a charged object.

Ques. How does an electric field vary with distance?

Ans. The electric field decreases as the distance between the charged object and the point of measurement increases.

Ques. What is an electric flux?

Ans. Electric flux is a measure of the amount of electric field passing through a given area. It is measured in volts per meter.

Ques. What is the purpose of an electric field?

Ans. The purpose of an electric field is to force charged objects to move in a particular direction. It also creates an electric potential difference between the two points.

Ques. What is the difference between voltage and potential difference?

Ans. Voltage is the measure of the potential difference between two points in an electric circuit. Potential difference is the measure of the electric potential difference between two points in an electric field.

Ques. What is the equation for electric potential?

Ans. The equation for electric potential is V=Q/4πεr. Where V is the electric potential, Q is the charge, and εr is the permittivity of free space.

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Long Answer Questions [3 Marks Questions]

Ques. An electron and a proton crossing along parallel routes enter a territory of the uniform magnetic field, working perpendicular to their ways. Which of them will go in a circular route with a higher frequency? 

Ans. The frequency of revolution is presented by

v = Bq/2πm ⇒ v ∝ 1/m.

As for me < mp, therefore, ve >vp

The proton will move in a circular path with a higher frequency. This is because the proton has more mass than the electron. The magnetic field strength (B) is the same for both particles, but the proton has a larger radius of revolution (rp) than the electron (re). This means that the proton will move in a circle with a higher frequency (v) than the electron.

Ques. A stationary electric charge creates an electric field around it. What is the direction of the electric field?

Ans. The electric field is directed away from the positive charge and towards the negative charge. This is because the positive charge creates a force on the negative charge and vice versa. The electric field is also perpendicular to the direction of the particle motion.

Ques. What is the electric field at a point in space? 

Ans. The electric field at a point in space is the force that the electric field exerts on a unit of positive charge at that point. It is measured in newtons per coulomb (N/C).

Ques. How does the electric field vary with distance? 

Ans. The electric field decreases as the distance between the charged object and the point of measurement increases. This is because the electric field is a direct result of the electric charge at that point. As the distance between the two points increases, the charge decreases, and so does the electric field.

Ques. What is an electric flux? (CBSE 2017)

Ans. Electric flux is a measure of the amount of electric field passing through a given area. It is measured in volts per meter (V/m).

Electric flux is related to the electric field by the following equation:

Φ = E A

Where Φ is the electric flux, E is the electric field, and A is the area. This equation states that the electric flux is equal to the electric field multiplied by the area.

Also check: P-n Junction


Very Long Answer Questions [5 Marks Questions] 

Ques. What is the potential difference between two points if a charge of 1 coulomb is placed at one point and a charge of 2 coulombs is placed at the other point?

Ans. The potential difference between the two points is 1 volt.

The potential difference between two points is equal to the work done in moving a unit of charge from one point to the other point. In this case, 1 coulomb of charge is moved from one point to the other. The work done is 1-volt x 1 coulomb = 1 volt.

Ques. A point charge of 1 coulomb is placed at the origin of an x-y coordinate system. A second point charge of 2 coulombs is placed at the point (2, 3). What is the electric potential at the point (4, 5)?

Ans. The electric potential at the point (4, 5) is 4 volts.

The electric potential at a point in space is determined by the amount of charge at that point and the strength of the electric field. In this case, there are two point charges: 1 coulomb at the origin and 2 coulombs at (2, 3). The electric potential at (4, 5) is the sum of the electric potentials at those two points.

Ques. What is the electric flux through a square with sides of length L if the electric potential at one corner is V?

Ans. The electric flux through a square with sides of length L is Φ = EL.

The electric flux through a square is proportional to the electric potential at each corner. In this case, the electric potential at one corner is V. Therefore, the electric flux through the square is Φ = EL = (V)L.

Ques. What is the purpose of an electric field?

Ans. The purpose of an electric field is to force charged objects to move in a particular direction. It also creates an electric potential difference between the two points.

An electric field is a force that acts on charged objects. It creates an electric potential difference between the two points. 

The greater the charge of the object, the greater the force of the electric field. The electric field also causes charged objects to move in a particular direction.

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CBSE CLASS XII Related Questions

  • 1.
    Write any two features of nuclear forces.


      • 2.
        A ray of light MN is incident normally on the face corresponding with side AB of a prism with an isosceles right-angled triangular base ABC. Trace the path of the ray as it passes through the prism when the refractive index of the prism material is \( \sqrt{2} \), and \( \sqrt{3} \).


          • 3.
            A 500 nm photon is incident normally on a perfectly reflecting surface and is reflected. The value of momentum transferred to the surface is:

              • \( 3.87 \times 10^{-43} \, \text{kg} \, \text{ms}^{-1} \)
              • \( 2.5 \times 10^{-30} \, \text{kg} \, \text{ms}^{-1} \)
              • \( 2.65 \times 10^{-27} \, \text{kg} \, \text{ms}^{-1} \)
              • \( 1.33 \times 10^{-27} \, \text{kg} \, \text{ms}^{-1} \)

            • 4.
              A circular coil of 100 turns and radius \( \left(\frac{10}{\sqrt{\pi}}\right) \, \text{cm}\) carrying current of \( 5.0 \, \text{A} \) is suspended vertically in a uniform horizontal magnetic field of \( 2.0 \, \text{T} \). The field makes an angle \( 30^\circ \) with the normal to the coil. Calculate:
              the magnetic dipole moment of the coil, and
              the magnitude of the counter torque that must be applied to prevent the coil from turning.


                • 5.
                  Suppose a pure Si crystal has \( 5 \times 10^{28} \) atoms per \( \text{m}^3 \). It is doped with \( 5 \times 10^{22} \) atoms per \( \text{m}^3 \) of Arsenic. Calculate majority and minority carrier concentration in the doped silicon. (Given: \( n_i = 1.5 \times 10^{16} \, \text{m}^{-3} \))


                    • 6.
                      The energy of an electron in an orbit in hydrogen atom is \( -3.4 \, \text{eV} \). Its angular momentum in the orbit will be:

                        • \( \dfrac{3h}{2\pi} \)
                        • \( \dfrac{2h}{\pi} \)
                        • \( \dfrac{h}{\pi} \)
                        • \( \dfrac{h}{2\pi} \)
                      CBSE CLASS XII Previous Year Papers

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