Assertion :Two equal unlike charge particles of mass $m_{1}$ and $m_{2}$ are moving in a plane with speeds $u_{1}$ and $u_{2}$ respectively. A uniform magnetic field is applied perpendicular to the plane. Both the particle leave tracks as shown in the Figure. Then, $m_{1} u_{1} > m_{2} u_{2}$ Reason: Eventhough a uniform magnetic field does no work on the moving charge, lt may accelerate the charge.

Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

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Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion

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Assertion is correct but Reason is incorrect

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Both Assertion and Reason are incorrect

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Solution

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
$\frac{m_{1} u_{1}^{2}}{r_{1}} = q u_{1} B$ $∴ r_{1} = \frac{m_{1} u_{1}}{q B}, r_{2} = \frac{m_{2} u_{2}}{q B}$
Since $r_{1} > r_{2}, m_{1} u_{1} > m_{2} u_{2}$
No work is done by the field $(Δ K = 0)$ , speed remains same but the velocity is changed - circular motion, hence accelerated motion

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The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertionm1u21r1=qu1B ∴r1=m1u1qB,r2=m2u2qBSince r1>r2,m1u1>m2u2No work is done by the field (ΔK=0), speed remains same but the velocity is changed - circular motion, hence accelerated motion