GATE 2022 PH – Question 33
A pulse lasts $10^{-3}$ s. Photon momentum uncertainty is of order $10^{-N}$ kg m/s. Find N, using $c=3\times10^8$ m/s and $h=6.6\times10^{-34}$ J s.
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Correct answer: 39
Explanation
The estimate $\Delta p\sim\hbar/(c\Delta t)$ is $3.5\times10^{-40}$ kg m/s, near the 10^-39 decade when uncertainty factors are ignored.