Medium
MCQ
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PYQ · JEE Mains 2025
Given below are two statements :
Statement (I): It is impossible to specify simultaneously with arbitrary precision, both the linear momentum and the position of a particle.
Statement (II) : If the uncertainty in the measurement of position and uncertainty in measurement of momentum are equal for an electron, then the uncertainty in the measurement of velocity is $\geqslant \sqrt{\frac{h}{\pi}} \times \frac{1}{2 m}$.
In the light of the above statements, choose the correct answer from the options given below :
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A
<p><b>Statement I</b> is false but <b>Statement II</b> is true</p>
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B
<p>Both <b>Statement I</b> and <b>Statement II</b> are true</p>
Correct answer
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C
<p>Both <b>Statement I</b> and <b>Statement II</b> are false</p>
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D
<p><b>Statement I</b> is true but <b>Statement II</b> is false</p>
Solution
<p>Statement I : Correct</p>
<p>This statement is describing the uncertainty principle.</p>
<p>It states that it is impossible to measure both the position and the momentum of an object.</p>
<p>Statement II : Correct.</p>
<p>If the uncertainty in the measurement of position ($\Delta x$) and the uncertainty in the measurement of momentum ($\Delta p$) are equal for an electron, then the uncertainty in the measurement of velocity ($\Delta v$) is greater than or equal to $\sqrt{\frac{h}{\pi}}\frac{1}{2m}$</p>
<p>This is derived from the Heisenberg uncertainty principle, $\Delta x\,.\,\Delta {p_x} \ge {h \over {4\pi }}$</p>
<p>Given, $\Delta x = \Delta p$</p>
<p>Substitute this in $\Delta x\,.\,\Delta p \ge {h \over {4\pi }}$ as</p>
<p>$\Delta p\,.\,\Delta p \ge {h \over {4\pi }}$</p>
<p>$\Delta {p^2} \ge {h \over {4\pi }}$</p>
<p>$\Delta {p^2} \ge {h \over {4\pi }}$</p>
<p>$$\left\{ \matrix{
The\,formula\,for\,momentum\,(P)\,is\,P = mV \hfill \cr
For\,uncerta{\mathop{\rm int}} y\,\Delta P = m\Delta v \hfill \cr} \right.$$</p>
<p>So, $m\Delta v \ge \sqrt {{h \over {4\pi }}}$</p>
<p>$\Delta v \ge \sqrt {{h \over {4\pi }}} \times {1 \over m}$</p>
<p>$\Delta v \ge {1 \over 2} > \sqrt {{h \over \pi }} > {1 \over m}$</p>
<p>$\Delta v \ge \sqrt {{h \over \pi }} {1 \over {2m}}$</p>
<p>Both the statements are true (correct). So answer is (2) Both statement I and statement II are true.</p>
About this question
Subject: Chemistry · Chapter: Atomic Structure · Topic: Bohr's Model
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