A positive, singly ionized atom of mass number $A_{\mathrm{M}}$ is accelerated from rest by the voltage $192…

A positive, singly ionized atom of mass number $A_{\mathrm{M}}$ is accelerated from rest by the voltage $192 \mathrm{~V}$. Thereafter, it enters a rectangular region of width $w$ with magnetic field $\vec{B}_0=0.1 \hat{k}$ Tesla, as shown in the figure. The ion finally hits a detector at the distance $x$ below its starting trajectory. [Given: Mass of neutron/proton $=(5 / 3) \times 10^{-27} \mathrm{~kg}$, charge of the electron $=1.6 \times 10^{-19} \mathrm{C}$.] Which of the following option(s) is(are) correct?
  1. The value of $x$ for $H^{+}$ion is $4 \mathrm{~cm}$.
  2. The value of $x$ for an ion with $A_{\mathrm{M}}=144$ is $48 \mathrm{~cm}$.
  3. For detecting ions with $1 \leq A_{\mathrm{M}} \leq 196$, the minimum height $\left(x_1-x_0\right)$ of the detector is $55 \mathrm{~cm}$.
  4. The minimum width $w$ of the region of the magnetic field for detecting ions with $A_{\mathrm{M}}=196$ is $56 \mathrm{~cm}$.

Solution

$ \begin{aligned} & \mathrm{x}=2 \mathrm{R} \\ & \Rightarrow \mathrm{x}=2 \frac{\mathrm{P}}{\mathrm{qB}} \Rightarrow \mathrm{x}=\frac{2 \sqrt{2 \mathrm{mqV}}}{\mathrm{qB}} \Rightarrow \mathrm{x}=\frac{2}{\mathrm{~B}} \sqrt{\frac{2 \mathrm{mV}}{\mathrm{q}}} \end{aligned} $ Option A For $\mathrm{H}^{+} \rightarrow \mathrm{m}=\frac{5}{3} \times 10^{-27} \mathrm{~kg}$ $\therefore x=\frac{2}{0.1} \sqrt{\frac{2 \times \frac{5}{3} \times 10^{-27} \times 192}{1.6 \times 10^{-19}}}=4 \mathrm{~cm}$ Option B For $\mathrm{A}_{\mathrm{m}}=144$ $x=\frac{2}{0.1} \sqrt{\frac{2 \times 144 \times \frac{5}{3} \times 10^{-27} \times 192}{1.6 \times 10^{-19}}}=48 \mathrm{~cm}$ Option C for $\mathrm{A}_m=1$ $\mathrm{x}=4 \mathrm{~cm} \&$ for $\mathrm{A}_{\mathrm{m}}=196$ $\mathrm{x}=56 \mathrm{~cm}$. so $\mathrm{x}_0=4 \mathrm{~cm} \& \mathrm{x}_1=56 \mathrm{~cm}$ $\therefore \mathrm{x}_1-\mathrm{x}_0=52 \mathrm{~cm}$. Option D Minimum width $=R$ for $\mathrm{A}_{\mathrm{M}}=196$ $\begin{aligned} & \mathrm{R}=\frac{\mathrm{P}}{\mathrm{qB}}=\frac{\sqrt{2 \mathrm{mqV}}}{\mathrm{qB}} \\ & \mathrm{R}=\frac{1}{\mathrm{~B}} \sqrt{\frac{2 \mathrm{mV}}{\mathrm{q}}} \\ & \mathrm{w}_{\min }=\mathrm{R}=\frac{1}{0.1} \sqrt{\frac{2 \times 196 \times \frac{5}{3} \times 10^{-27} \times 192}{1.6 \times 10^{-19}}}=28 \mathrm{~cm} \end{aligned}$

Asked in: JEE Advanced 2024 (Paper 2)

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