If an electron is not deflected in passing through a certain region of space can we be sure that there is no magnetic field in that region?

Explanation

To determine whether we can be sure that there is no magnetic field in a region of space where an electron is not deflected, we can analyze the situation using the Lorentz force equation. Here’s a step-by-step solution:

### Step 1: Understand the Lorentz Force Equation
The Lorentz force \( \mathbf{F} \) acting on a charged particle (like an electron) moving in electric and magnetic fields is given by:
\[ \mathbf{F} = q\mathbf{E} + q\mathbf{v} \times \mathbf{B} \]
where:
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