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suchintan mondal Grade: 12
        

1)a radioactive material has mean life 1620 yrs and 540 yrs for alpha-emission and beta- emission respectively.The time in which half of the material remains undecayed emitting both these radiations is________


2)mass of 2 curie uranium(234)is_______


3)Half life of radium is 1620yrs &its atomic weight =226kg/kilomole.No. of atoms that will decay from 1 gm. of sample per second will be _________


4)Ratio of momenta of an electron of mass me and an alpha particle of mass ma which are accelerated from rest by a potential difference of 250V is_______

7 years ago

Answers : (2)

Askiitians expert Anirudh iitk
8 Points
										

Answer to qsn no 4:


the kinetic energy = qV. In either case the q has same numerical value.( since an alpha particle is a hydrogen nucleus = +1 unit charge wheras an electron  has -1 unit charge)


so, the kinetic energy has same value


hence p^2/2m is the same. therefore,  (p1/p2)^2 = (m1/m2). the required ratio is therefore sqrt of (me/ma)

7 years ago
Askiitians expert Anirudh iitk
8 Points
										

nswer to qsn no 3:


226g/mol => 226 g of the material will have avagadros number of atoms. hence, 1 g will have A/226 atoms. Now in this case, this is the starting amterial ie N0 . And it is a first order eaction.


hence, N = N0e-kt


-dN/dt = kN0e-kt. U know K from half life and if u adjust the units in terms of seconds ie. 1620x365x24x60x60 sec,then put t=0 in the above eqn. You will get the rate of decomposition in terms of atoms/sec for initial conc. this is the answer u seek

7 years ago
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