A charged particle moves through a magnetic field perpendicular to its direction. Then

  • Option 1)

    kinetic energy changes but the momentum is constant

  • Option 2)

    the momentum changes but the kinetic energy is constant

  • Option 3)

    both momentum and kinetic energy of the particle are not constant

  • Option 4)

    both, momentum and kinetic energy of the particle are constant

 

Answers (1)

As we learnt in

Radius of charged particle -

r=\frac{mv}{qB}=\frac{P}{qB}=\frac{\sqrt{}2mk}{qB}=\frac{1}{B}\sqrt{}\frac{2mV}{q}

-

 

 

Due to Lorentzian force, F=qv\times B , When a charged particle enters a field with its velocity perpendicular to the magnetic field, the motion is circular with qvB=\frac{mv^{2}}{r}.    v constantly changes its direction (but not the magnitude). Therefore its tangential momentum changes its direction but its energy remains the same \left (\frac{1}{2}mv^{2}=constant \right ).

Therefore the answer is (b).

 


Option 1)

kinetic energy changes but the momentum is constant

Incorrect option

Option 2)

the momentum changes but the kinetic energy is constant

Correct option

Option 3)

both momentum and kinetic energy of the particle are not constant

Incorrect option

Option 4)

both, momentum and kinetic energy of the particle are constant

Incorrect option

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