A beam of alpha particles is fired horizontally with a speed of 4.8 105 m/s into a region where there is a vertical magnetic field of magnitude 0.123 T. An alpha particle is the nucleus of a helium atom and as such, consists of two protons, two neutrons, and has a mass of 6.64 10-27 kg.

How long does it take for an alpha particle to move halfway through a complete circle?

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Answer:

The time taken for the alpha particle is 5.301x10⁻⁷s

Explanation:

The centripetal force is equal:

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

The magnetic force is equal:

[tex]F_{m} =Bqv[/tex]

Matching both expressions:

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

Where

m = 6.64x10⁻²⁷kg

v = 4.8x10⁵m/s

B = 0.123 T

q = 1.6x10⁻¹⁹C

[tex]r=\frac{6.64x10^{-27}*4.8x10^{5} }{0.123*2*1.6x10^{-19} } =0.081m[/tex]

The time taken for the alpha particle is:

[tex]t=\frac{\pi r}{v} =\frac{\pi 0.081}{4.8x10^{5} } =5.301x10^{-7}s[/tex]

The time taken for the alpha particle is [tex]5.301*10^{-7}s[/tex]

Centripetal Force:

  • The force that is necessary to keep an object moving in a curved path and that is directed inward toward the center of rotation.
  • It is given by:

[tex]F_c=\frac{mv^2}{r}[/tex] .........(i)

where,

m= mass of the body

v= velocity

r= radius

The magnetic force will be:

[tex]F_m=Bqv[/tex]............(ii)

Thus, on computing two equations:

[tex]\frac{mv^2}{r} =Bqv\\\\r=\frac{mv}{Bq}[/tex].............(iii)

Given:

  • m = 6.64x10⁻²⁷kg
  • v = 4.8x10⁵m/s
  • B = 0.123 T
  • q = 1.6x10⁻¹⁹C

Substituting the values in equation (iii).

[tex]r=\frac{6.64*10^{27}*4.8*10^5}{0.123*2*1.6*10^{-19}} \\\\r=0.081m[/tex]

The time taken for the alpha particle is:

[tex]t=\frac{\pi*r}{v}\\\\ t=\frac{3.14*0.081}{4.8*10^5} \\\\t=5.301*10^{-7}s[/tex]

Thus, the time taken for the alpha particle is [tex]5.301*10^{-7}s[/tex].

Find more information about Centripetal force here:

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