Question

a)A very long, straight wire carries a current of 17.1 A out of the screen. An electron outside the wire is 1.29 cm to the right of the central axis of the wire and is moving with a speed of 4.45×10⁶ m/s. Find the magnitude of the magnetic force on the electron if it is moving directly away from the wire (i.e., rightward).

b) Find the magnitude of the force on the electron if it is moving parallel to the wire in the direction of the current (i.e., out of the screen)

c)Find the magnitude of the force on the electron if it is moving upward.

Answer 1

Magnetic field due to the wire,

B = u0*i / 2*pi*r

B = 4*pi*10^(-7)*17.1 / 2*pi*0.0129

B = 2.65*10^(-4) T (upwards)

(a)

magnitude of the magnetic force on electron,

F = q (v x B)

it is moving directly away from the wire (rightwards)

F = 1.6*10^(-19)*(4.45*10^6 * 2.65*10^(-4)) (i x j)

F = 1.88*10^(-16) N (outwards)

(b)

if it is moving parallel to the wire in the direction of the current,

F = 1.6*10^(-19)*(4.45*10^6 * 2.65*10^(-4)) (k x j)

F = 1.88*10^(-16) N (leftwards)

(c)

if it is moving upward,

F = 1.6*10^(-19)*(4.45*10^6 * 2.65*10^(-4)) (j x j)

F = 0