Final answer:
In a uniform magnetic field directed in the z direction, a sample with moving charges will experience a magnetic force perpendicular to the direction of the magnetic field and their velocity, determined by the right-hand rule. Charges moving parallel to the magnetic field do not experience any force.
Step-by-step explanation:
When a uniform magnetic field is applied to a sample in the z direction, the effect of the magnetic field on the sample depends on whether there are moving charges inside it. If there are moving charged particles within the sample, and they are moving in a direction other than the z direction, they will experience a magnetic force. However, if these charges are moving parallel to the uniform magnetic field (in the z direction), they will not experience any force, as the magnetic force acts perpendicular to the velocity of the moving charges and the magnetic field.
For example, an alpha particle moving in the positive x-direction will experience a force in the y direction, while one moving in the negative y-direction will experience a force in the x direction. Conversely, if the alpha particle is moving in the same direction as the magnetic field (positive z-direction), it will not experience any force.
To determine the direction of the magnetic force on a moving charge, one can employ the right-hand rule: Point your fingers in the direction of the velocity, align your palm with the direction of the magnetic field, and your thumb then points in the direction of the magnetic force on a positive charge. The strength of the magnetic force is determined by the charge's velocity, the magnetic field's magnitude, and the sine of the angle between the velocity and the magnetic field vectors.
Using this rule to calculate the force on an electron or proton shows that while the force on both will be equal in magnitude, they will be opposite in direction due to their opposite charges. However, because the electron has much less mass than the proton, it will experience a much greater acceleration.