22.4 Magnetic Field Strength: Force on a Moving Charge in a Magnetic Field

A proton moves in the –x-direction and encounters a uniform magnetic field pointing in the +x-direction. In what direction is the resulting magnetic force on the proton?

1. The proton experiences no magnetic force.
2. +x-direction
3. −y-direction
4. +y-direction

What is the maximum magnitude of the force on an aluminum rod with a $0 . \text{100} -\mu\text{C}$ charge that you pass between the poles of a 1.50-T permanent magnet at a speed of 5.00 m/s? In what direction is the force?

(a) A cosmic ray proton moving toward the Earth at $\text{5}.\text{00} \times \text{10}^{7} \text{m}/\text{s}$ experiences a magnetic force of $1 . \text{70} \times \text{10}^{- \text{16}} \text{N}$. What is the strength of the magnetic field if there is a $\text{45}º$ angle between it and the proton’s velocity? (b) Is the value obtained in part (a) consistent with the known strength of the Earth’s magnetic field on its surface? Discuss.

(a) A physicist performing a sensitive measurement wants to limit the magnetic force on a moving charge in her equipment to less than $1 . \text{00} \times \text{10}^{- \text{12}} N$. What is the greatest the charge can be if it moves at a maximum speed of 30.0 m/s in the Earth’s field? (b) Discuss whether it would be difficult to limit the charge to less than the value found in (a) by comparing it with typical static electricity and noting th…