Exams › JEE Main › Physics
Given below are two statements: One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): In an uniform magnetic field, speed and energy remains the same for a moving charged particle. Reason (R): Moving charged particle experiences magnetic force perpendicular to its direction of motion.
- Both (A) and (R) are true and (R) is the correct explanation of (A).
- Both (A) and (R) are true but (R) is NOT the correct explanation of (A).
- (A) is true but (R) is false.
- (A) is false but (R) is true.
Correct answer: Both (A) and (R) are true and (R) is the correct explanation of (A).
Solution
The assertion is correct because in a uniform magnetic field, the magnetic force acts perpendicular to the velocity of the charged particle, causing it to move in a circular path without changing its speed or kinetic energy. The reason accurately explains this phenomenon, as the perpendicular force does not do work on the particle, thus maintaining its speed and energy.
Related JEE Main Physics questions
- A tightly wound solenoid has 2000 turns and a cross-sectional area of $1.5 \times 10^{-4}\,\text{m}^2$. It carries a current of 2.0 A and is hung at its center with its axis perpendicular to its length so that it can rotate in a horizontal plane. If it is placed in a uniform magnetic field of strength $5 \times 10^{-2}\,\text{T}$, and the field makes an angle of $30^\circ$ with the solenoid axis, what torque acts on the solenoid?
- A cyclotron with dee radius $R$ is used to speed up protons of mass $m$. An alternating electric field of frequency $\nu$ is applied across the dees. For the cyclotron to operate, the magnetic field $B$ and the kinetic energy $K$ of the emerging proton beam are related by:
- A long, straight conductor of radius $a$ carries a constant current $I$ that is spread uniformly over its cross-sectional area. What is the ratio of the magnetic field at a distance $a/2$ from the axis to the magnetic field at a distance $2a$ from the axis?
- Two tangent galvanometers, A and B, have coil radii of 8 cm and 16 cm respectively, and each has a resistance of 8 $\Omega$. They are joined in parallel. When the applied voltages are 4 V and 6 V respectively, the corresponding deflections in A and B are 30$^\circ$ and 60$^\circ$. If galvanometer A has 2 turns, the number of turns in B is
- A charge of $2\,\mu\text{C}$ revolves with a frequency of $6.25\times 10^{12}\,\text{Hz}$ and creates a magnetic field of $6.28\,\text{T}$ at a point on the circle. What is the radius of the circular path?
- An electron beam travels through a region where uniform electric and magnetic fields act mutually perpendicular to each other, and both are also perpendicular to the direction of motion of the electrons. If the electric field strength is $20\,\text{V m}^{-1}$ and the magnetic field strength is $0.5\,\text{T}$, the speed of the electrons must be
⚔️ Practice JEE Main Physics free + battle 1v1 →