In a radioactive substance at t = 0, the number of atoms is 8×104, its half-life period is 3 yr. The number of atoms equal to 1×104 will remain after an interval of:

1. 9 yr

2. 8 yr 

3. 6 yr 

4. 24 yr

Subtopic:  Radioactivity (OLD NCERT) |
 73%
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PMT - 2010
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What is the respective number of α and β-particles emitted in the following radioactive decay?

X90200Y80168   

1. 6 and 8

3. 6 and 6

3. 8 and 8

4. 8 and 6   

Subtopic:  Types of Decay |
 72%
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The half-life of radium is 1622 years. How long will it take for seven-eighth of a given amount of radium to decay

1. 3244 years

2. 6488 years

3. 4866 years

4. 811 years

Subtopic:  Radioactivity (OLD NCERT) |
 71%
From NCERT
PMT - 1999
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The mass of a proton is 1.0073 u and that of the neutron is 1.0087 u (u = atomic mass unit) The binding energy of H2e4 is (mass of helium nucleus = 4.0015 u)

1. 28.4 MeV

2. 0.061 u

3. 0.0305 J

4. 0.0305 erg

Subtopic:  Mass-Energy Equivalent |
 68%
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The binding energies of the nuclei A and B are Ea and Eb respectively. Three atoms of the element B fuse to give one atom of element A and an energy Q is released. Then Ea, Eb and Q are related as:

1. Ea-3Eb=Q 

2. 3Eb-Ea=Q

3. Ea+3Eb=Q 

4. Eb+3Ea=Q

Subtopic:  Nuclear Binding Energy |
 52%
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A free neutron decays into a proton, an electron and:

1. A beta particle.

2. An alpha particle.

3. An antineutrino.

4. A neutrino.

Subtopic:  Types of Decay |
 64%
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In a radioactive sample the fraction of initial number of radioactive nuclei, which remains undecayed after n mean lives is:

1. 1en 

2.  en   

3. 1-1en 

4. 1e-1n

Subtopic:  Radioactivity (OLD NCERT) |
 54%
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The activity of a radioactive sample is measured as 9750 counts/min at t = 0 and as 975 counts/min at t = 5 min. The decay constant is approximately:

1. 0.922/min           

2. 0.691/min         

3. 0.461/min           

4. 0.230/min

Subtopic:  Radioactivity (OLD NCERT) |
 54%
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The energy equivalent of one atomic mass unit is:
1. \(1.6\times 10^{-19}~\text{J}\)
2. \(6.02\times 10^{23}~\text{J}\)
3. \(931~\text{MeV}\)
4. \(9.31~\text{MeV}\)

Subtopic:  Mass-Energy Equivalent |
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Solar energy is due to:

1. fusion reaction. 2. fission reaction.
3. combustion reaction. 4. chemical reaction.
Subtopic:  Nuclear Energy |
 66%
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