JAMB - Physics (1990 - No. 41)
A substance has a half of 3mins. after 6mins. the count rate was observed to be 400. What was its count rate at zero time?
200
1200
1600
2400
Vysvetlenie
Let the count rate at zero time be K
Count rate after 3mins, = \(\frac{K}{2}\)
Count rate after 6mins = \(\frac{K}{4}\)
but count after 6mins = 400 ( given )
Then = \(\frac{K}{4}\) = 400
K = 4 X 400 = 1600
∴ = count rate at zero time = 1600.