NEET Physics Nuclei Questions Solved

BOARD

(a) State the law of radioactive decay. Write the SI unit of 'activity'.

(b) There are 42 ×106 radioactive nuclei in a given radioactive sample. If the half life of the sample is 20 s, how many nuclei will decay in 10 s?                               

                                                                                                             3 marks

(a) Statement : Rate of decay of a given radioactive sample is directly propotional to the total number of undecayed nuclei present in the sample.                              (1)mark

[Alternatively: dNdtN]

Unit- becquerel(Bq)                                                                           (1/2)mark

(b) N=N0e-λt /NN0=12n                                                                                1/2markn=tT1/2=1020=12                                                                                    1/2markN=42×106×121/2                                                                         1/2mark=4×106nuclei                                      

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