MHT-CET : Physics Entrance Exam

### MHT - CET : Physics - Atoms Molecules and Nuclei Page 6

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Activity (A) of a radioactive sample is the number of disintegrations occurring per unit time,

 A = | dN | = Nl dt

Curie: The activity of a radioactive sample is said to be one curie (1 ci)
if 3.7 × 1010 disintegrations occur per second.

Other unit: The SI unit : bequerel (Bq)

1. 1 Bq = 1 disintegration/S.
2. 1 rutherford (rd) = 106 disintegration/S.

9.

Mass and Energy Relation

According to Einstein's special theory of relativity

1. Variation of mass of a body with its speed is given by
 m = m0
1.
 where m0 = mass of particle when it is at rest n = velocity of particle c = velocity of light
1.
2. Energy and mass are equivalent and related by the equation

E

= mc2

\ E

 = m0c2

\ E

= m0c2 + k

 where m0c2 = rest energy of particle k = kinetic energy of particle.

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