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In a vacuum, a straight conductor has 18-A current that goes upward. An electron is traveling at 8.92 x 10^4 m/s. If the electron is 0.2 m from the conductor and its instantaneous velocity is parallel to the conductor (albeit heading downward), find the magnitude and direction of the force on the electron. Explain whether the force will be constant.

Here is my attempt:

Known:

I (current) = 18 A [upward]

v (speed) = 8.92 x 10^4 m/s

r (radius) = 0.2 m

q (charge) = 1.602 x 10^-19 C

Unknown:

Fe

F magnetic = F centripetal

qvB = (m x v^2) / r

Therefore,

B = mv / qr

= (9.11 x 10^-31) x (8.92 x 10^4) / (1.602 x 10^-19) x (0.20)

= 0.000002536 T

F magnetic = qvB sin[tex]Theta[/tex]

= (1.602 x 10^-19) x (8.92 x 10^4) x 0.000002536 x sin90

= 3.6 x 10^-20 N

I think it went horribly, horribly wrong. Was I supposed to use to F magnetic equation at all? It's difficult to know which F equation to use.

I'd appreciate any guidance with this problem. Thank you.

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# Homework Help: Force on electron as it travels through conductor

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