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  <h4>Statement</h4>
  <p>
    $10.2.8$
    A plane capacitor is placed in a homogeneous magnetic field od induction $B$ parallel to the plates. From point A, electrons enter perpendicularly to magnetic field direction. The tension (voltage) applied to the plates is $V$. What is the condition for which electrons pass through the capacitor? 
  </p>
  <center>
    <figure>
      <img src="statement.png"
        loading="lazy" alt="10.2.8" width="300" />
      <figcaption>
        For problem 10.2.8
      </figcaption>
    </figure>
  </center>
  <h4>Solution</h4>
  <p class="TxtSolutions">
    Electrons pass through capacitor if they don't collide with plates. So, supposing a capacitor of infinite length, electron's velocity must be parallel to the plates (or its horizontal range over a plate greater than its enter's height). This is possible if electric and magnetic forces are in equilibrium (equal absolute values and opposed directions).
  </p>
  <center>
    $evB = eE$
  </center>
  <center>
    $v = \frac{E}{B}$
  </center>
  <p calss="TxtSolutions">
    As $E=\frac{V}{h}$,
  </p>
  <center>
    $\boxed{v = \frac{V}{Bh}}$
  </center>
  <p class="TxtSolutions">
    This device is known as speed's selector.
  </p>
    <p class="TxtSolutions" style="text-align: right; font-style: italic; font-size: 14;">   
        BSc. Luis Daniel Fernández Quintana<br>
        Physics Department (FCNE)<br>
        Universidad de Oriente, Cuba<br>
    </p>
</article>