The half-life of C-14 is 5730 years. The measurement of the percentage of the C-

Question

The half-life of C-14 is 5730 years. The measurement of the percentage of the C-14 remained in a tree died was found to be 10.8%, how long the tree was left undisturbed after it died? 19, 680 yrs 945 yrs 18, 400 yrs A Geiger-Muller counter is a: photographic detector Cloud chamber gas ionization counter Which of the following processes decreases the atomic mass by two? alpha emission two neutrons emission two positrons emission Electron-capture which is also called K-Capture is associated with Conversion of a neutron to a proton Decrease in the atomic number Increase in mass number.

Explanation / Answer

(29) For a first order reaction rate constant , k = ( 2.303 /t )x log ( Mo/ M)

Where

Mo = initial mass = 100

M= Mass left after time t = 10.8

K = rate constant = 0.693 /t1/2

= 0.693 / 5730 yr-1

= 1.21x10-4 yr-1

t = time = ?

Plug the values we get t = ( 2.303 /k )x log ( Mo / M)

t = ( 2.303 /(1.21x10-4) )x log ( 100/10.8)

= 18406 years

(30) geiger muller counter is a type of gas-filled radiation detector

so option (c) is correct

(31) (a) alpha emission

(32) electron capture( -1 e0)

0n1 ---> 1H1 +  -1 e0

So option (a) is correct

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