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CBSE Class 12 Physics 2020 Delhi Set 2 Paper

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Question : 4 of 7
Marks: +1, -0
SECTION - B
(a) Define one Becquerel.
(b) A radioactive substance disintegrates into two types of daughter nuclei, one type with disintegration constant λ1\lambda_1 and the other type with disintegration constant λ2\lambda_2. Determine the half-line of the radioactive substance.
Solution:  
(a) Becquerel: One Becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second.
(b) λ=λ1+λ2\lambda = \lambda_1 + \lambda_2
Or,   0.693T1/2=λ1+λ2\; \frac{0.693}{T_{1 / 2}} = \lambda_1 + \lambda_2
∴    T1/2=  0.693λ1+λ2\therefore \; \; T_{1 / 2} = \; \frac{0.693}{\lambda_1 + \lambda_2}
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