Question

Two long, thin, parallel conductors are kept very close to each other, without touching. One carries a current i, and the other has charge λ per unit length. An electron moving parallel to the conductors is undeflected. Let c = velocity of light.

(a) v = λc2/i

(b) v = i/λ

(c) c = i/λ

(d) The electron may be at any distance from the conductor.

Answer 1

Correct Answer is: (a, d)

At P, electric field = E = λ/2πɛ0x (to the right),

and magnetic field = B = μ0i/2πx (into the paper).

For no deflection, E = vB

or v = E/B

or v = λ/2πɛ0x X 2πx/μ0i = λ/i 1/ɛ0μ0 =λc2/i .