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In a mass spectrometer, a single-charged particle (charge e) has a speed of 1.0 × 10 6 m/s and enters a uniform magnetic field of 0.20 T. The radius of the circular orbit is 0.020 m. What is the mass of the particle?

Answer :

Answer:

The mass is  [tex]m =6.4*10^{-28} \ kg[/tex]

Explanation:

From the question we are told that

   The  speed of the charge is  [tex]v = 1.0 *10^{6} \ m/s[/tex]

    The  magnetic field is  [tex]B = 0.20 \ T[/tex]

     The radius is [tex]r = 0.02 \ m[/tex]

      The value of the charge is  [tex]e = 1.60 *10^{-19} \ C[/tex]

The centripetal acting on the charge moving in the circular orbit is mathematically represented as

        [tex]F_c = \frac{mv^2}{r }[/tex]

Now this centripetal force is due to the force exerted on the charge by the magnetic field on the charge which is mathematically represented as

     [tex]F_m = qv B sin\theta[/tex]

At the maximum of this magnetic force [tex]\theta = 90 ^o[/tex]

So  

     [tex]F_m = e v B sin(90)[/tex]

      [tex]F_m = e v B[/tex]

Now given that it is this  magnetic force that is causing the circular motion we have that

       [tex]F_c = F_m[/tex]

=>     [tex]\frac{mv^2}{r } = ev B[/tex]

=>     [tex]m = \frac{e * B * r }{v }[/tex]

substituting values

       [tex]m = \frac{ 1.60 *10^{-19} * 0.20 * 0.020 }{1.0*10^{6} }[/tex]

     [tex]m =6.4*10^{-28} \ kg[/tex]

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