JAMB - Physics (1987 - No. 42)
A radioactive sample initially contains N atoms. After three half-lives the number of atoms that have disintegrated is
\(\frac{N}{8}\)
\(\frac{3N}{8}\)
\(\frac{5N}{8}\)
\(\frac{7N}{8}\)
คำอธิบาย
N \(\to\) \(\frac{N}{2}\) \(\to\) \(\frac{N}{4}\) \(\to\) \(\frac{N}{8}\)
Number of atoms left = 1-1/8=\(\frac{7N}{8}\)