The right-hand rule is typically used to determine the direction of the magnetic force exerted on a charged particle as it moves through a magnetic field. The rule is generally applied in the following way:
- Point your thumb in the direction of the velocity of the positive charge.
- Point your fingers in the direction of the magnetic field.
- The direction your palm pushes indicates the direction of the force experienced by a positive charge.
Based on the provided options, the most appropriate circumstance for using the right-hand rule would be:
When the particle is positive.
When dealing with a negative charged particle, you would actually need to reverse the direction of the force indicated by the right-hand rule to determine the force on that particle. However, the right-hand rule itself is defined for positive charges.