An electron and a proton move in circular orbits in a plane perpendicular to a uniform magnetic field B > . Find the ratio of the radii of their circular orbits when the electron and the proton have (a) the same momentum and (b) the same kinetic energy.

Respuesta :

[tex]\frac{mv}{qB}[/tex]Answer:  

a)  ratio of radii for same momentum  = 1

b)   ratio of radii for same energy           = 2.3 × [tex]10^{-2}[/tex]

Explanation:

using formula  for radius

                            r =   [tex]\frac{mv}{qB}[/tex]

                       where m is mass

                        v is velocity

                        q is charge

                        B is magnetic field

a) for same momentum radius will be inversely proportional to                                              roduct of charge and magnetic and magnetic field

                       r ∝  [tex]\frac{1}{qB}[/tex]

  since for proton and electron s charge and magnetic field is same so

                     [tex]\frac{r_{1} }{r_{2} } =\frac{1}{1}[/tex]

b) using relation b/w kinetic energy and momentum

                 p = [tex]\sqrt{2 KEm}[/tex]   ............(1)

where p is momentum and

   K.E is kinetic energy

 we know   [tex]r =\frac{mv}{qB}[/tex]

                  [tex]mv =qBr[/tex]

                  [tex]p = mv[/tex] = [tex]qBr[/tex]

 from first equation  

                 [tex]qBr = \sqrt{2KEm}[/tex]

since qB is same for electron and proton and energy is also         same(given)  

so we get

          [tex]\frac{r_{e} }{ r_{p} }[/tex][tex]= \sqrt{\frac{m_{e} }{m_{p } }[/tex]

         

           [tex]\frac{r_{e} }{r_{p} }[/tex][tex]= \sqrt{\frac{9.1 x 10^{-31} }{1.67 x 10^{-27} } } = 2.3 x 10 ^{-2}[/tex]