<h3 id="back-link"><a href="/#10.2">$\leftarrow$Back</a></h3>

    <h3> Statement </h3>
    <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>

    <h3>Solution</h3>
    <p>
      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).
      $$evB = eE$$
      $$v = \frac{E}{B}$$
      As $E=\frac{V}{h}$,
      $$\boxed{v = \frac{V}{Bh}}$$
      This device is known as speed's selector.
    </p>


    <p 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>



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