1. A uniform magnetic field points upward, parallel to the page, and has a magni

Question

1. A uniform magnetic field points upward, parallel to the page, and has a magnitude of 7.85 mT. A negatively charged particle (q = ?3.32 ?C, m = 2.05 pg) moves through this field with a speed of 67.3 km/s at a 42° with respect to the magnetic field, parallel to the page as shown. What is the direction of the magnetic force on this particle?

2. A uniform magnetic field points upward, parallel to the page, and has a magnitude of 7.85 mT. A negatively charged particle (q = ?3.32 ?C, m = 2.05 pg) moves through this field with a speed of 67.3 km/s perpendicular to the magnetic field, as shown. The magnetic force on this particle is a centripetal force and causes the particle to move in a circular path. What is the radius of the particle’s circular path?

A. To the left, parallel to the page B. Into the page C. Downward, parallel to the page D. To the right, parallel to the page E. Upward, parallel to the page F. Out of the page ???????? 42 9

Explanation / Answer

1) (B) Into the page.

Using right hand palm rule:

The right hand rule states that, to find the direction of the magnetic force on a positive moving charge, the thumb of the right hand point in the direction of v, the fingers in the direction of B, and the force (F) is directed perpendicular to the right hand palm.

The direction of the force F on a negative charge is in the opposite sense to that above (so pointed away from the back of your hand).

2)

Equate magnetic force with centripetal force:

FB = Fc

=> qvB = mv2/r

=> r = mv/qB

= 5.29mm

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