MCQ
For two statements are given $-$ one labelled Assertion $(A)$ and the other labelled Reason $(R).$ Select the correct answer to these questions from the codes $\ce{(a), (b), (c)}$ and $(d)$ as given below :
Assertion : When a charged particle moves perpendicular to magnetic field then its kinetic energy and momentum gets affected.
Reason : Force does not change velocity of charged particle.
  • A
    Both $A$ and $R$ are true, and $R$ is correct explanation of the assertion.
  • B
    Both $A$ and $R$ are true, but $R$ is not the correct explanation of the assertion.
  • C
    $A$ is true, but $R$ is false.
  • $A$ is false, but $R$ is true.

Answer

Correct option: D.
$A$ is false, but $R$ is true.
When a charged particle moves perpendicular to magnetic field, it experiences a force which changes the direction of motion of the particle without changing the magnitude of velocity of the particle. Hence, kinetic energy remains constant but momentum of electron changes.

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