Electron Velocity in Crossed Fields

Electron Velocity in Crossed Fields (1996)

Question: Electrons move undeflected through perpendicular \( E = 20 \, \text{V/m} \) and \( B = 0.5 \, \text{T} \). Their velocity is:

(a) 8 m/s

(b) 5.5 m/s

(c) 20 m/s

(d) 40 m/s

Solution

Step 1: Force Balance
For undeflected motion: \[ qE = qvB \implies v = \frac{E}{B} \]

Step 2: Calculation
\[ v = \frac{20 \, \text{V/m}}{0.5 \, \text{T}} = 40 \, \text{m/s} \]

Answer: Option (d) \( 40 \, \text{m/s} \) is correct.