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A Van de Graaff generator is one of the original particle accelerators and can be used to accelerate charged particles like protons or electrons. You may have seen it used to make human hair stand on end or produce large sparks. One application of the Van de Graaff generator is to create x-rays by bombarding a hard metal target with the beam. Consider a beam of protons at 1.10 keV and a current of 4.65 mA produced by the generator.
(a) What is the speed of the protons?
(b) How many protons are produced each second?

Respuesta :

Solution :

Given that :

The energy of the protons, K.E. = 1.10 keV

                                                    [tex]$= 1.10 \times 10^3 \ eV $[/tex]

The current produced by the generator is I = 5 mA

                                                                        [tex]$= 5 \times 10^{-3} \ A$[/tex]

Now [tex]$1 \ eV = 1.6 \times 10^{-19 }\ J$[/tex]

Mass of the proton, m = [tex]$1.67 \times 10^_{-27} $[/tex] kg

Charge of the proton, [tex]$q_p = 1.6 \times 10^{-19} \ C$[/tex]

a). Therefore using the formula for K.E. we can find out the velocity of the proton.

[tex]$K.E. =\frac{1}{2}mv^2$[/tex]

[tex]$v=\sqrt{\frac{2K.E.}{m}}$[/tex]

[tex]$v=\sqrt{\frac{2\times 10^3 \times 1.6 \times 10^{-19}}{1.67 \times 10^{-27}}}$[/tex]

  [tex]$= 4.38 \times 10^5 \ m/s$[/tex]

b). We know that the current is :

 [tex]$I=\frac{\Delta Q}{\Delta t}$[/tex]

Therefore, the total charge in one second is given by :

[tex]$\Delta Q = I \times \Delta t$[/tex]

     [tex]$= 5 \times 10^{-3} \times 1$[/tex]

    [tex]$= 5 \times 10^{-3}\ C$[/tex]

So, the number of protons in this charge is given by :

[tex]$n = \frac{\Delta Q}{q_p}$[/tex]

  [tex]$=\frac{5 \times 10^{-3} }{1.6 \times 10^{-19}}$[/tex]

  [tex]$= 3.13 \times 10^{16}$[/tex] protons