Answer to Question #324553 in Physics for Justin

Question

A long straight wire carries a current of 1.0 A.

(a) At what distance from the wire is the magnitude of the magnetic field

equal to 2.5 x 10^-5 T?

(b)What is the magnitude of the magnetic force that this wire will exert on a

3.0 nC particle moving at 4.2 x 10^4 m/s perpendicular to the field at that

distance?

Answer 1

(a)

$B=\frac{\mu_0I}{2\pi r}$

$r=\frac{\mu_0I}{2\pi B}=\frac{4\pi*10^{-7}*1.0}{2\pi*2.5*10^{-5}}=0.008\;\rm m$

(b)

$F=qvB\\ =3.0*10^{-9}*4.2*10^4*2.5*10^{-5}=3.2*10^{-9}\:\rm N$