A charged particle is moving in a uniform magnetic field. Which of the following statements concerning the magnetic force exerted on the particle is false?
A) It does not change the kinetic energy of the particle.
B) It can act only on a particle in motion.
C) It increases the speed of the particle.
D) It changes the velocity of the particle.
E) It does no work on the particle.
What is your thinking on this? The magnetic force acts perpendicular to the path of motion.
answer is c
D) it changes the velocioty of the particle, because to find the velocity we need to know the mass, the gravational pull and the heigh of the particle (potential energy) and if any one of these things change then the velocity also changes. And because the magnetic force is acting on the partical the gravational pull would change meaning the veolcity changes.
Actually, the correct answer is E) It does no work on the particle.
To understand why, let's consider the magnetic force equation: F = qvBsinθ, where F is the magnetic force, q is the charge of the particle, v is its velocity, B is the magnitude of the magnetic field, and θ is the angle between the velocity and the magnetic field.
1) A) It does not change the kinetic energy of the particle: The magnetic force acts perpendicular to the velocity of the particle, which means θ is 90 degrees. Therefore, the sinθ term becomes 1, and the magnitude of the force only depends on the charge, velocity, and the magnitude of the magnetic field, without affecting the kinetic energy.
2) B) It can act only on a particle in motion: Since the magnetic force equation involves velocity (v), the force can act only on a particle in motion.
3) C) It increases the speed of the particle: This statement is false. The magnetic force acts perpendicular to the velocity, making the force independent of the speed. It only changes the direction of the charged particle's motion.
4) D) It changes the velocity of the particle: This statement is true. Even though the magnetic force changes only the direction of the velocity, the velocity itself (magnitude and direction) is affected since the path of the particle is altered.
5) E) It does no work on the particle: This statement is true. Work is defined as the dot product of force and displacement. The magnetic force is always perpendicular to the displacement of the particle, meaning the angle θ is 90 degrees. In this case, the sinθ term becomes 1, resulting in zero work done by the magnetic force.
Therefore, the false statement is C) It increases the speed of the particle.