Three fourth of the active nuclei decay in a radioactive sample in 3/4 s. The half-life of the sample is

(1) 12 s          (2) 1 s             (3) 38 s             (4) 34 s

Concept Questions :-

Radioactivity
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What is the radius of iodine atom? (atomic no. 53, mass no. 126) [1988]

(1) 2.5×10-11 m

(2) 2.5×10-9 m

(3) 7×10-9 m

(4) 7×10-6 m

Concept Questions :-

Mass-energy equivalent
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Which of the following statements is true for nuclear forces? [1990]

(1) They obey the inverse square law of distance.

(2) They obey the inverse third power law of distance.

(3) They are short range forces.

(4) They are equal in strength to electromagnetic forces.

Concept Questions :-

Mass-energy equivalent
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The ratio of the radii of the nuclei A13l27 and T52e125 is approximately [1990]

(1) 6 : 10               (2) 13 : 52              (3) 40 : 177                (4) 14 : 73

Concept Questions :-

Mass-energy equivalent
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Bragg's law for X-rays is 

(1) d sin θ= 2 nλ                          (2) 2d sin θ= nλ

(3) n sin θ= 2 λd                          (4) None of these

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The relationship between disintegration constant λ and half-life [T] will be:

(1) λ=log10 2T                    (2) λ=loge 2T

(3) λ=Tloge 2                      (4) λ=log2 eT

Concept Questions :-

Radioactivity
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Alpha particles are 

(1) 2 free protons

(2) helium atoms

(3) singly ionized helium atoms

(4) doubly ionised helium atoms

Concept Questions :-

Mass-energy equivalent
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A radioactive sample with a half-life of 1 month has the label: 'Activity = 2 microcurie on 1-8-1991'. What would be its activity two months earlier? 

(1) 1.0 microcurie       

(2) 0.5 microcurie           

(3) 4 microcurie             

(4) 8 microcurie

Concept Questions :-

Radioactivity
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If the nuclear force between two protons, two neutrons and between proton and neutron is denoted by Fpp, Fnn and Fpn respectively, then [1991]

(1) FppFnnFpn

(2) FppFnn and Fpp=Fnn

(3) Fpp=Fnn=Fpn

(4) FppFnnFpn

Concept Questions :-

Nuclear binding energy
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A radioactive element has half-life period 800 yr. After 6400 yr, what fraction will remain? [1989]

(1) 12              (2) 116            (3) 18              (4) 1256

Concept Questions :-

Radioactivity
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