# 3 - Atomic Physics Questions Answers

A point source of light is placed at the centre of curvature

of a hemispherical surface. The radius of curvature is r

and the inner surface is completely reflecting. Find the

force on the hemisphere due to the light falling on it if

the source emits a power W.

**Asked By: ANKIT SHARMA**

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*Consider an electron trapped in an infinite well whose width is 98.5 pm. If it is in a state with n = 15, what are (i) its energy? (ii) the uncertainty in its momentum? (iii) the uncertainty in its position?*

**Asked By: ANKIT SONI**

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**Joshi sir comment**

$Letwidth=b\phantom{\rule{0ex}{0ex}}Fornthstaten\frac{\lambda}{2}=b\Rightarrow \lambda =\frac{2b}{n}\phantom{\rule{0ex}{0ex}}NowE=\frac{{p}^{2}}{2m}=\frac{{\left({\displaystyle \raisebox{1ex}{$h$}\!\left/ \!\raisebox{-1ex}{$\lambda $}\right.}\right)}^{2}}{2m}\phantom{\rule{0ex}{0ex}}Solveafterputtingthevalueof\lambda \phantom{\rule{0ex}{0ex}}Uncer\mathrm{ta}intyinposition=b\phantom{\rule{0ex}{0ex}}Nowuse\u2206p.\u2206x=nh/2\mathrm{\pi}\mathrm{for}\mathrm{finding}\mathrm{uncertainty}\mathrm{in}\mathrm{momentum}$

a toy car of mass 500g travels with a uniform velocity of 25m/s for 5 seconds, the brakes are then applied and the car is uniformly retarded and comes to rest in further 10s calculate the retardation

**Asked By: SARABJEET**

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**Joshi sir comment**

use v = u + at

u = 25, v = 0 and t = 10