2021 Moving Charges and MagnetismLorentz Force Medium Question 1 of 10 in Lorentz Force

An infinitely long straight conductor carries a current of 5 A as shown. An electron is moving with a speed of $10^5\ m/s$ parallel to the conductor. The perpendicular distance between the electron and the conductor is 20 cm at an instant. Calculate the magnitude of the force experienced by the electron at that instant.

A $8\pi\times10^{-20}\ N$
B $4\pi\times10^{-20}\ N$
C $8\times10^{-20}\ N$
D $4\times10^{-20}\ N$

The answer is C.

Solution

Field due to the wire at the electron: $B = \frac{\mu_0 i}{2\pi r}$
$F = evB = ev\left(\frac{\mu_0 i}{2\pi r}\right) = \frac{1.6 \times 10^{-19} \times 10^5 \times 2 \times 10^{-7} \times 5}{0.2}$
$F = 8 \times 10^{-20}$ N

Concept force on an electron near a current-carrying wire

Lorentz Force in past papers

10 questions from this chapter have appeared across 8 exam years.