Question

Radioactive dating works by measuring the

	ratio of isotopes
	amount of radioactivity absorbed
	radioactivity left
	time it takes for the radioactivity to disappear

The half-life of Cr-51 is about a month. If only 12.5% of the original sample remains, the time passed is about

	3 months
	a year and a half
	4 days
	3 weeks

Uranium gets split into smaller atoms in

	black holes
	nuclear power plants
	CAT scans
	electrolytic cells

Answer 1

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The half-life of Cr-51 is about a month.

t_1/2 = 1 month

k = ln2 / t_1/2 (Decay constant)

12.5% of the original sample remains.

Let's time passed is t.

Use decay law:

N_t = N*e^-kt

12.5% = 100%*e^-kt

0.125 = e^-kt ( take natural logarithm both side)

ln 0.125 = -kt

ln 0.125 = -(ln 2/1 month)t (Put value of k.)

t = -(ln 0.125)/(ln 2) month

t = -(-3) month = 3 month

( 3 months is correct answer.)

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Uranium gets split into smaller atoms in nuclear power plants.