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»

1000 days
300 days
10 days
100 days

Solution :Activity `(-(dN)/(dt)) prop N`
`N = N_(0) ((1)/(2))^(n) RARR (N)/(N_(0)) = ((1)/(2))^(n)`
`(1)/(10) = ((1)/(2))^(n) rArr 10 = 2^(n)`
`LOG 10 = n log 2 rArr n = (1)/(0.301) = 3.32`
`t = n XX t_(1//2) = 3.32 xx 30 = 99.6` days


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