What percentage of original radioactive atoms is left after five half lives 
(a) 0.3%                (b) 1%
(c) 31%                  (d) 3.125%

Concept Questions :-

Radioactivity
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Beta rays emitted by a radioactive material are

(a) Electromagnetic radiation
(b) The electrons orbiting around the nucleus
(c) Charged particles emitted by nucleus
(d) Neutral particles

Concept Questions :-

Types of decay
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Alpha rays emitted from a radioactive substance are

(a) Negatively charged particles
(b) Ionised hydrogen nuclei
(c) Doubly ionised helium atom
(d) Uncharged particles having the mass equal to proton

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Half life of Bi210 is 5 days. If we start with 50,000
atoms of this isotope, the number of atoms left over after 10
days is 
(a) 5,000                (b) 25,000
(c) 12,500              (d) 20,000

Concept Questions :-

Radioactivity
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A nucleus of atomic mass A and atomic number Z emits β-particles. The atomic mass and atomic number of the resulting nucleus are 
(a) A, Z              (b) A + 1, Z
(c) A, Z + 1        (d) A-4, Z-2 

Concept Questions :-

Types of decay
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The radioactivity of a certain radioactive element drops to 1/64 of its initial value in 30 seconds. Its half life is

(a) 2 seconds               (b) 4 seconds
(c) 5 seconds               (d) 6 seconds

Concept Questions :-

Radioactivity
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Radioactivity was discovered by
(a) Becquerel            (b) Pierre Curie
(c) Roentgen             (d) Rutherford

Concept Questions :-

Radioactivity
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The average life T and the decay constant λ of a radioactive nucleus are related as 
(a) =1               (b) T=0.693λ
(c) Tλ=1               (d) T=cλ

Concept Questions :-

Radioactivity
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If T is the half life of a radioactive material, then the fraction that would remain after a time T2 is 
(a) 12              (b) 34
(c) 12           (d) 2-12

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If the decay or disintegration constant of a radioactive substance is λ, then its half life and mean life are respectively 
(a) 1λ and  loge2λ              (b) loge2λ and 1λ

(c) λloge2 and 1λ               (d) λloge2 and 1λ

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