a)

Which of the following is incorrect regarding magnetic lines of the field?  

A. The direction of the magnetic field at a point is taken as the direction in which the north pole of a magnetic compass needle points. 

B. Magnetic field lines are closed curves. 

C. If magnetic field lines are parallel and equidistant, they represent zero field strength. 

D. The relative strength of the magnetic field is shown by the degree of closeness of the field lines.  

 

                                                                                 OR

b)

Which of the following proton characteristics can change when it freely flows through a magnetic field? (There may be more than one answer.)  

A. Mass

B. Speed

C. Velocity 

D. Momentum  

a) 

The incorrect statement is if magnetic field lines are parallel and equidistant, they represent zero field strength. Magnetic field lines appear parallel when they are far away from the magnet, but that doesn’t mean that field strength is zero.  

Some properties of magnetic field lines are  

1. Magnetic field lines are directed from the north pole to the south pole. 
2. Magnetic field lines are closed and continuous. 
3. If magnetic field lines are parallel and equidistant, they represent a uniform magnetic field.  

Hence the correct option is (c) If magnetic field lines are parallel and equidistant, they represent zero field strength. 

                                                                                               OR

b) When a proton enters a magnetic field, it starts moving in a circular path, and each moving charged particle in a magnetic field experiences a force. This force affects the velocity and momentum of a proton. The force can change the proton’s direction (velocity) but not its speed(magnitude). As a result, the momentum and velocity of the proton change. 

Hence, the correct options are (c) Velocity and (d) Momentum.