Which force field can increase a moving electron’s speed?
a. both of these
b. electric field
c. magnetic field
d. neither of these
The correct answer and explanation is:
The correct answer is b. electric field.
An electric field is the force field that can increase the speed of a moving electron. Here’s why:
- Electric Field: An electric field exerts a force on a charged particle such as an electron. The force is given by F=qEF = qE, where qq is the charge of the electron and EE is the electric field strength. Since the electric field acts in the direction of the field, it can accelerate the electron by imparting kinetic energy to it. The kinetic energy of the electron increases, and as a result, its speed increases. In simple terms, an electric field can do work on the electron, speeding it up.
- Magnetic Field: On the other hand, a magnetic field does not change the speed of a moving electron. The magnetic force on a moving electron is given by F=qvBsin(θ)F = qvB \sin(\theta), where vv is the velocity of the electron, BB is the magnetic field strength, and θ\theta is the angle between the velocity and the magnetic field. The magnetic force is always perpendicular to the electron’s velocity, meaning it does not affect the electron’s speed, only its direction of motion. The electron’s trajectory can be bent by the magnetic field, but its speed (magnitude of velocity) remains unchanged.
In conclusion, while a magnetic field can alter the direction of the electron’s motion, it cannot increase or decrease its speed. In contrast, an electric field can accelerate the electron, thus increasing its speed by doing work on it.