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If two point charges \(q\) of a sufficiently large mass move parallel to one another with the same non-relativistic velocity "' (shown in the figure), the ratio of the qe\(\longrightarrow \vec{v}\) magnitude of the magnetic and electric interaction forces q between charges is: (a) \(\frac{v}{c}\) (b) \(\frac{c}{v}\) (c) \(\frac{c^{2}}{v^{2}}\) (d) \(\frac{v^{2}}{c^{2}}\)

Short Answer

Expert verified
The correct answer is (d) \(\frac{v^2}{c^2}\).

Step by step solution

01

Understanding the forces involved

The two point charges exert both electric and magnetic forces on each other. The electric force is given by Coulomb's Law, and the magnetic force arises due to their motion and is described by the Biot-Savart Law and Lorentz Force Law.
02

Calculating the Electric Force

The electric force between two point charges is determined using Coulomb's Law: \[ F_e = \frac{k q^2}{r^2} \]where \( k \) is Coulomb's constant, \( q \) is the charge magnitude, and \( r \) is the distance between the charges.
03

Calculating the Magnetic Force

According to the Biot-Savart Law, a charge moving with velocity \( v \) will create a magnetic field. The resultant magnetic force on another moving charge \( q \) is given by:\[ F_m = q v B \]where the magnetic field \( B \) due to a moving charge is given by:\[ B = \frac{ k q v}{c^2 r^2} \]Thus, the magnetic force is:\[ F_m = \frac{k q^2 v^2}{c^2 r^2} \]
04

Calculate the Ratio of Forces

The ratio of the magnitudes of the magnetic to electric interaction forces is:\[ \frac{F_m}{F_e} = \frac{\frac{k q^2 v^2}{c^2 r^2}}{\frac{k q^2}{r^2}} \]Simplifying gives:\[ \frac{F_m}{F_e} = \frac{v^2}{c^2} \]
05

Identify the Correct Answer

The ratio \(\frac{v^2}{c^2}\) matches option (d), so the correct answer is option (d).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Coulomb's Law
Coulomb's Law is a fundamental principle that explains how electric charges interact with each other. It describes how the force between two charges depends on their magnitudes and the distance separating them. Here’s how Coulomb’s Law works:
  • The electric force (\( F_e \)) between two point charges is directly proportional to the product of their charges. Mathematically, this is expressed as \( F_e \propto q_1 q_2 \).
  • It is also inversely proportional to the square of the distance between the charges, denoted as \( F_e \propto \frac{1}{r^2} \).
  • The constant of proportionality is Coulomb’s constant \( k \), which equals approximately \( 8.99 \times 10^9 \, \text{N m}^2/\text{C}^2 \).
The equation for Coulomb’s law is written as: \[ F_e = \frac{k q_1 q_2}{r^2} \] Thus, it is essential for understanding the electric force, which can be attractive or repulsive, depending on whether the charges are unlike or like respectively. Coulomb's Law helps us realize the crucial role electric force plays in the interactions at an atomic and molecular level.
Biot-Savart Law
The Biot-Savart Law explains how a magnetic field (\( B \)) is generated by moving electric charges. It is particularly useful for calculating the magnetic field resulting from a current or moving point charges.Consider the fundamentals of the Biot-Savart Law:
  • The law states that a magnetic field is created by a moving charge or current, and its magnitude is proportional to both the current and the velocity of the charge.
  • This magnetic field is inversely proportional to the square of the distance from the moving charge, similar to the inverse-square relationship in Coulomb's Law.
  • The magnetic field direction is given by the right-hand rule, following the direction of current flow or velocity.
The mathematical form of the Biot-Savart Law for point charges is often written as: \[ B = \frac{\mu_0 q v}{4 \pi r^2} \] In this scenario, \( \mu_0 \) is the permeability of free space, and it connects the electric current or charge to the magnetic field.By understanding the Biot-Savart Law, one can calculate the strength and orientation of the magnetic field produced by moving charges, laying the groundwork for more complex magnetic force interactions.
Lorentz Force Law
The Lorentz Force Law is crucial for determining the force exerted on a charged particle moving through electromagnetic fields. It combines the effects of electric and magnetic fields on charged particles.Key aspects of the Lorentz Force Law include:
  • The total force (\( F \)) acting on a charged particle is the sum of the electric and magnetic forces.
  • The electric component is given by \( q \times E \), where \( E \) is the electric field.
  • The magnetic component is expressed as \( q (v \times B) \), where \( v \) is the velocity of the particle and \( B \) is the magnetic field.
In mathematical terms, the Lorentz Force is: \[ F = q(E + v \times B) \] This equation shows how every charge experiences a force influenced by both its movement and the fields it encounters.It's important to note:- The force derived from the electric field is parallel, while the magnetic part is perpendicular to the velocity.- The Lorentz Force Law is the foundation for understanding phenomena like the motion of charged particles in magnetic fields and the operation of technologies like the cyclotron.By mastering the Lorentz Force Law, one gains insights into how charged particles behave in various electromagnetic conditions, which is vital for applications ranging from everyday electronics to advanced scientific research.

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Most popular questions from this chapter

A coil carrying electric current is placed in uniform magnetic field. Then: (a) torque is formed (b) emf is induced (c) both (a) and (b) are correct (d) none of the above.

In a certain region uniform electric field \(E\) and magnetic field \(B\) are present in the opposite direction. At the instant \(t=0\), a particle of mass \(m\) carrying a charge \(q\) is given velocity \(v_{0}\) at an angle \(\theta\), with the \(y\) -axis, in the \(y-z\) plane. The time after which the speed of the particle would be minimum is equal to: (a) \(\frac{m v_{0}}{q E}\) (b) \(\frac{m v_{0} \sin \theta}{q E}\) (c) \(\frac{m v_{0} \cos \theta}{q E}\) (d) \(\frac{2 \pi m}{q B}\)

Two long parallel wires are placed on a smooth horizontal table. They have equal and opposite charges. Work required to increase the separation between wires from \(a\) to \(2 a\) if magnitude of charge per unit length on them is \(\lambda\), will be : (a) \(\frac{\lambda^{2} \ln 2}{4 \pi \varepsilon_{0}}\) (b) \(\frac{\lambda^{2}}{\pi \varepsilon_{0}} \ln 2\) (c) \(\frac{\lambda^{2}}{4 \pi \varepsilon_{0} a}\) (d) \(\frac{\lambda^{2}}{2 \pi \varepsilon_{0}} \ln 2\)

Mark correct option or options: (a) The current sensitivity of a galvanometer is defined as the deflection in milimeters produced on a scale placed at a distance of one metre from the galvanometer mirror, when a current of \(10^{-6}\) A passes through galvanometer coil (b) Current sensitivity \(=\mathrm{NAB/C}\) (c) Charge sensitivity \(=\frac{2 \pi}{T} \times\) current sensitivity (d) all the above

A wire of arbitrary shape carries a current \(I=2 \mathrm{~A}\). consider the portion of wire between \((0,0,0)\) and \((4 \mathrm{~m}\), \(4 \mathrm{~m}, 4 \mathrm{~m}\) ). A magnetic field given by \(\overrightarrow{\mathrm{B}}=1.2 \times 10^{-4} \mathrm{~T} \hat{\mathrm{i}}+2.0 \times 10^{-4} \mathrm{~T} \hat{\mathrm{j}}\) exists in the space. The force acting on the given portion is: (a) incalculatable as length of wire is not known (b) \(\overrightarrow{\mathrm{F}}=[(\hat{\mathrm{i}}+\hat{\mathrm{j}}+\hat{\mathrm{k}}) \times(1.2 \hat{\mathrm{i}}+2.0 \hat{\mathrm{j}})] \mathrm{N}\) (c) \(\overrightarrow{\mathbf{F}}=8 \times 10^{-4}[(\hat{1}+\hat{j}+\hat{k}) \times(1.2 \hat{i}+2.0 \hat{j})] \mathrm{N}\) (d) \(\overrightarrow{\mathbf{F}}=8 \times 10^{-4}[(1.2 \hat{\mathbf{i}}+2.0 \hat{\mathbf{j}}) \times(\hat{\mathbf{i}}+\hat{\mathbf{j}}+\hat{\mathbf{k}})] \mathrm{N}\)

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