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Elbobo

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## Homework Statement

A magnetic field of 0.1 T forces a proton beam

of 1.5 mA to move in a circle of radius 0.1 m.

The plane of the circle is perpendicular to the

magnetic field.

Of the following, which is the best estimate

of the work W done by the magnetic field on

the protons during one complete orbit of the

circle?

1. W = 0 J

2. W = 10^22 J

3. W = 10^−22 J

4. W = 10^20 J

5. W = 10^−5 J

## Homework Equations

F = qVB = ILB

F = mv^2 / r

C = 2 pi*r

## The Attempt at a Solution

Since work is energy, I used the formula for kinetic energy...

W = 1/2 mv^2

F

_{centripetal}= F

_{magnetic}

mv^2 /r = qvB

v = rqB / m

W = 1/2 m (rqB / m)^2

W = 1/2 (1.6725 x 10^-27) * (0.1 * 1.602 x 10^-19 * 0.1 / 1.6725 x 10^-27) ^2

W = 7.67235874 x 10^-16 J

This isn't close to any of the answer choices. Can someone help me?

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