NEET Physics Nuclei Questions Solved

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The half-life of a sample of a radioactive substance is 1 hour. If 8×1010 atoms are present at t = 0, then the number of atoms decayed in the duration t = 2 hour to t = 4 hour will be
(a) 2×1010          (b) 1.5×1010
(c) Zero               (d) Infinity

 (b) N=N012tT1/2 
No of atoms at t = 2hr, N1=8×10101221=2×1010
No. of atoms at t = 4hr, N2=8×10101241=12×1010
 No. of atoms decayed in given duration

=2-12×1010=1.5×1010

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