1.

A radioactive element gets spilled over the floor of a room. Its half-life period is 30 days. If the initial activity is ten times the permissible value, after how many days will it be safe to enter the room ?

Answer»

300 days
10 days
100 days
1000 days.

Solution :LET the PERMISSIBLE activity limit be x, then INITIAL activity would be 10x
`lamda=(0.693)/(30"days")`
`t=(2.303)/(lamda)log"([A]_(0))/([A])`
`=(2.303xx30)/(0.693)"log"(10x)/(x)`
`=99.7"days"~~100` days.


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