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551.

The figure indicates the enegry level diagram of an atom and the origin of six spectral lines in emission (e.g. line no.`5` series from the transition from level `B` to `A`). The following spectral lines will also occur in the absorption spectrum A. 1,4,6B. 4,5,6C. 1,2,3D. 1,2,3,4,5,6

Answer» Correct Answer - C
Discussion
552.

The wavelength of yellow line of sodium is `5896 Å`. Its wave number will beA. `50883 xx 10^(10)` per secondB. `16961` per `cm`C. `17581` per `cm`D. `50883` per `cm`

Answer» Correct Answer - B
Wave number `bar(v) = (1)/(lambda) = (1)/(5896 xx 10^(-8)) = 16961` per m
Discussion
553.

An `alpha`-particle with a kinetic energy of `2.1eV` makes a head on collision with a hydrogen atom moving towards it with a kinetic energy of `8.4 eV`. The collisionA. must be perfectly elasticB. may be perfectly inelasticC. may be inelasticD. must be perfectly inelastic

Answer» Correct Answer - C
The maximum kinetic energy avaiable for transition to potential energy`//` exclination energy is:
`(1)/(2).(m_(alpha)m_(H))/(m_(alpha)+m_(H)).(V_(rel))^(2)`
`=(4m_(1),m_(H))/(5m).(v_(alpha)+v_(H))^(2) " "=(2m)/(5).(v_(alpha)^(2)+v_(H)^(2)+2v_(alpha)v_(H))`
`(2m)/(5)[(2.E_(alpha))/(4m)+(2E_(4))/(m)+2sqrt((2E.alpha)/(4m).(2E_(H))/(m))=(2)/(5)[(2.1)/(2)+2xx8.4+2xxsqrt(2.1xx8.4)]`
`=10.5 eV gt 10.2 eV`
Hence, inelastic collision is possible.
Discussion
554.

In an experiment on photoelectric effect, the emitter and the collector plates are placed at a separation of 10cm and are connected through an ammeter without any cell. A magnetic field B exists parallel to the plates. The work function of the emitter is 2.39 e V and the light incident on it has wavelengths between 400nm and 600nm. Find the minimum value of B for which the current registered by the ammeter is zero. Neglect any effect of space charge.

Answer» Correct Answer - `57`
Discussion
555.

A stationary hydrogen atom emits photon corresponding to the first line of Lyman series. If R is the Rydberg constant and M is the mass of the atom, then the velocity acquired by the atom isA. `(3)/(4) (R h)/(M)`B. `(R h)/(4 M)`C. `(R h)/(2 M)`D. `(R h)/(M)`

Answer» Correct Answer - A
From conservation of momentum:
`M V = (h)/(lambda) = h R (1 - 1/(4)) implies V = (3)/(4) (h R)/(M)`
Discussion
556.

A stationary hydrogen atom emits a photon corresponding to first line of the Lyman series. What velocity does the atom acquire?

Answer» Correct Answer - `(E)/(c ).(1)/(m)=(13.6xx3e)/(4cm_(p))=3.25m//s`
Energy of the first line in Lyman series
`E=13.6xx(1-(1)/(4))eV=10.2 eV`
Velocity of atoms `=(p)/(m)=(E)/(c ).(1)/(m)=(10.2xx1.6xx10^(-19))/(3xx10^(8)xx1.67xx10^(-24))m//s=3.25 m//s`
Discussion