Q. No.A radioactive sample has a half-life of 1770 years. At some instant, 20% of the sample has decayed. If taking this instant as , it is found that at , 20% of the sample is left, then is:
1. 1770 years
2. 885 years
3. 2655 years
4. 3540 years
If the half-life of a radioactive substance is 10 hours, then its mean life is:
1. 14.4 h
2. 7.2 h
3. 20 h
4. 6.93 h
In the given decay equation, \(\mathrm{A}\) and \(\mathrm{B}\) indicate:
| 1. | Electron and antineutrino |
| 2. | Positron and antineutrino |
| 3. | Positron and neutrino |
| 4. | Electron and positron |
| 1. | Decreases by \(4\) and mass number remains same. |
| 2. | Remains the same but the mass number increases by \(4\). |
| 3. | Remains the same but mass number decreases by \(8\). |
| 4. | Increases but mass number remains same. |
| 1. | \(\dfrac{8 A + 2}{A + 1}\) | 2. | \(\dfrac{8 A - 2}{A + 1}\) |
| 3. | \(\dfrac{8 A - 1}{A + 1}\) | 4. | \(\dfrac{8 A}{A + 1}\) |
The statement which is incorrect about nuclear force between two protons is?
| 1. | These are always attractive forces. |
| 2. | These are non-central forces. |
| 3. | These are charge independent. |
| 4. | These are short-range forces. |
1. \(V\propto M\)
2. \(V\propto \frac{1}{M}\)
3. \(V\propto M^3\)
4. \(V\propto \frac{1}{M^3}\)
A sample of radioactive material has initial mass A, decay constant B, molecular weight C and Avogadro's constant D. The activity of the sample after time, t, will be:
1.
2.
3.
4.
1. \(2X\)
2. \(\frac{X}{3}\)
3. \(4X\)
4. \(X\)
The activity of a radioactive substance decays from 8000 becquerel to 4000 becquerel in 5 days. The activity of the substance after the next 10 days will be:
1. 500 becquerel
2. 1500 becquerel
3. 2000 becquerel
4. 1000 becquerel
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