Question

SI unit of radioactivity is:
(A) Becquerel
(B) Curie
(C) Weber
(D) Gauss

Answer 1

You should know the SI unit of magnetic flux density, magnetic flux. You should also have the knowledge that Si unit of radioactivity was changed by the international system of units.

Complete Solution :
Going by the options;
(a) Gauss- This is the SI unit of magnetic induction (or magnetic flux density)
(b) Weber – This is the SI unit of magnetic flux.
Now we're left with Curie and Becquerel.
(c) Curie used to be the SI unit of radioactivity but in 1975, Becquerel replaced Curie.

- The activity of a quantity of radioactive material in which one nucleus decays per second is termed as one Becquerel. Becquerel is named after the physicist Henry Becquerel, who was the first person to discover evidence of radioactivity.
Hence, the SI unit of radioactivity is Becquerel.
So, the correct answer is “Option A”.

Additional Information : 1. Curie is named after Pierre curie and Marie Curie. One Curie is approximately the activity of 1 gram of radium.
2. Henri Becquerel discovered the phenomenon of radioactivity but the student, Marie Curie named it so. Marie Curie also discovered radioactivity elements radium, thorium and polonium.

Note: 1 Curie = $3.7\times {{10}^{10}}$ disintegrations per second. On the other hand, 1 Becquerel equals 1 disintegration per second. Therefore, we can say that, $1\text{ }Curie=3.7\times {{10}^{10}}Becquerel\left( Bq \right)$.
Other units of radioactivity are:
- millicurie (mCi)
- microcurie ($\text{ }\\!\\!\mu\\!\\!\text{ Ci}$)
- Rutherford (rd)