A proton is moving North in a region where the magnetic field is pointing downwa
ID: 1554582 • Letter: A
Question
A proton is moving North in a region where the magnetic field is pointing downward. In what direction does the magnetic force on the proton point?
The magnetic force on the proton points downwards.
The magnetic force on the proton points North.
The magnetic force on the proton points West.
d. The magnetic force on the proton points East.
Uniform electric and magnetic fields are tuned so that an electron moving at a particular speed v in the positive x direction feels no net force (the electric and magnetic forces balance). What will happen to a proton traveling in the positive x direction at the same speed v?
The proton will also feel no net force.
The proton will feel a net force in the positive y direction.
The proton will feel a net force in the negative y direction.
The proton will feel a net force in the negative x direction.
a.The magnetic force on the proton points downwards.
b.The magnetic force on the proton points North.
c.The magnetic force on the proton points West.
d. The magnetic force on the proton points East.
Uniform electric and magnetic fields are tuned so that an electron moving at a particular speed v in the positive x direction feels no net force (the electric and magnetic forces balance). What will happen to a proton traveling in the positive x direction at the same speed v?
a.The proton will also feel no net force.
b.The proton will feel a net force in the positive y direction.
c.The proton will feel a net force in the negative y direction.
d.The proton will feel a net force in the negative x direction.
Explanation / Answer
1) Using fleming's left hand rule, in which fore finger points towards magnetic field, middle finger towards the direction of the velocity of the charged particle and thumb points toward the direction of the magnetic force experienced by it, when kept in mutually perpendicular direction. Therefore, placing middle finge towards north and forefinger toward downward direction, the thumb points towards the east. Hence, the correct option is (d)
2) The electron is moving in positive x direction. Let a magnetic force be applied on the electron perpendicular to its direction of velocity. According to the above stated rule, the force due to magnetic field will act perpendicular to the plane containing the velocity vector and magnetic field vector. Now, electric force will be in opposite direction to the magnetic force i.e., making an angle of 180o with the magnetic force. We know that the electric force due to electric field acts in a direction opposite to that of electric field, therefore, the electric field applied is in the direction of the magnetic force.i.e., positive y direction. Hence the proton movine in positive x direction will experience a force in positive y direction. Therefore the correct option is (b)
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