A mixture consists of two radioactive materials A₁ and A₂ with half lives of 20s and 10s respectively. Initially the mixture has 40g of A₁ and 160g of A₂. The active amount of the two in the mixture will becomes equal after :
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Question

A mixture consists of two radioactive materials A₁ and A₂ with half lives of 20s and 10s respectively. Initially the mixture has 40g of A₁ and 160g of A₂. The active amount of the two in the mixture will becomes equal after :

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G1 Physics · Accepted Answer

Step 1: Use N(t) = N₀ exp(−λt), A = λN and T₁/₂ = ln2/λ. Step 2: For two samples, write the decay law separately and equate the required activities/numbers. Final: B: 40s.