CBSE 2026 · Region 3 · Set 1 · Q20 · 2 marks
A particle of mass M at rest splits up into two particles of masses $\displaystyle \mathrm{m}_{1}$ and $\displaystyle \mathrm{m}_{2}$ having non-zero velocities. Calculate the ratio of the de Broglie wavelengths associated with the two particles.
Marking-scheme solution
Calculating the ratio of de-Broglie ccording to law of conservation of m
\[\begin{aligned}
\mathrm{m}_{1} v_{1}-\mathrm{m}_{2} v_{2} & =0 \\
\mathrm{m}_{1} v_{1} & =\mathrm{m}_{2} v_{2} \\
\frac{v_{1}}{v_{2}} & =\frac{\mathrm{m}_{2}}{\mathrm{m}_{1}} \\
\frac{\lambda_{1}}{\lambda_{2}} & =\frac{h}{\mathrm{m}_{1} v_{1}} \times \frac{\mathrm{m}_{2} v_{2}}{h} \\
& =\frac{\mathrm{m}_{2} v_{2}}{\mathrm{m}_{1} v_{1}} \\
& =\frac{\mathrm{m}_{2}}{\mathrm{m}_{1}} \times \frac{\mathrm{m}_{1}}{\mathrm{m}_{2}} \\
& =1 \\
\lambda_{1}: \lambda_{2} & =1: 1
\end{aligned}
\] from
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