At time t_1, an electron is sent along the positive direction of an x axis, thro

Question

At time t_1, an electron is sent along the positive direction of an x axis, through both an electric field E and a magnetic field B, with E directed parallel to the y axis. The figure gives the y component F_net, y of the net force on the electron due to the two fields, as a function of the electron's speed v at time t_1. The scale of the velocity axis is set by v_s = 110 m/s. The x and z components of the net force are zero at t_1. Assuming B_x = 0, find (a) the magnitude of the electric field and (b) B in unit-vector notation.

Explanation / Answer

in y- direction,

Fnet = Fe + Fm

Fe is independent of v. (it will be constant throughout) but Fm increases with velocity.

so from it, we can say that Fe is negative and Fm is positive.

( v is in -ve x direction so B will be along -z axis)

Fnet = (q B) v + Fe

putting v = 0

Fnet at 0sec = Fe = q E

2 x 10^-9 = 1.6x 10^-19 E

E = 1.25 N/C ,,,,,,,,,,Ans(A)

(B) slope of F vs v is q B .

q B = (4 x 10^-19) / 110

B = 0.0227 T

vector B = - 0.0227 T k

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