Question

Which of the following properties of a proton can not change while it moves freely in a magnetic field ?
(Multiple option can be correct)
A) Mass
B) Speed
C) Velocity
D) Momentum

Answer 1

Hint
The magnetic field is full of charges and the proton gets repelled, resulting in a change in its direction. So, the property based on direction changes, whereas the property based on the magnitude value remains constant throughout the magnetic field.

Complete Step By Step Solution
As we know that magnetic field consists of free charges, where the attract or repel the particle entered. Here we have a proton, which is inserted in the magnetic field. As we know that, the magnetic field does not change in mass of any particle travelled. It just repels and changes the direction of motion of the particle. So, as we go through the options.
Option (A) denotes Mass, which is a scalar quantity and thus is the correct option where it remains unchanged throughout the motion of protons in the magnetic field.
Option (B) denotes speed, which is too a scalar quantity and leads to the correct answer.
Option (C) denotes a vector which depends upon direction and hence it changes throughout the motion. So, option (C) is an incorrect option.
Lastly, Option (D) denotes Momentum, which is mass into velocity. This is too not a scalar quantity. hence it changes in the magnetic field. Hence option (D) is an incorrect option.
Thus, Option (A) and (B) are correct.

Note
Magnetic field lines emerge from north pole to south pole and the density of magnetic field lines increases as distance decreases.