1 mg of thorium emits 22 `alpha-` particles per minute per unit solid angle.Calculate average - life of thorium.Atomic weight of thorium-232.

The atomic weiht of radium is 226 .It is observed that 3.67 xx 10^(10) alpha - particles are emitted per second from one gramp of radium.Calculate in years the half-life period of radium.

A fresh radioactive mixture contians short lived sppecies A and B. Both emitting alpha -particles intially of 8000 alpha particles per minute. 20 minutes later, they emis at the rate of 3500 alpha -particles per minute. If the half-lives of the species A and B are 10 minutes and 500 hours respectively, then the ratio of activities of A: B the intial mixture was:

A current of 2.4 A flows through a wire of cross-sectional area 1.5 mm^2 . Find the current density in the wire. If the wire contains 8 xx 10^28m^-3 elecrtrons per unit volume calculate the average relaxation on time. Given that charge on electron = 1.6 xx 10^-19C and mass of electron =9.1 xx 10^-31 kg.

A rectangular coil 25 cm xx 10 cm and having 700 turns rotates about an axis at right angles to a magnetic field of 20 gauss at 1,500revolutions per minute. Calculate the maximum vlaue of the e.m.f. generated in the coil.

A face centred cubic lattice of a single type of atoms has same defects and it one corner and one face centre is left unoccupied per unit cell. Calculate the packing fraction of such solid.

The nucleus of an atom of ._(92)Y^(235) initially at rest decays by emitting an alpha particle. The binding energy per nucleon of parent and dougther nuclei are 7.8MeV and 7.835MeV respectively and that of alpha particles is 7.07MeV//"nucleon". Assuming the dougther nucleus to be formed in the unexcited state and neglecting its share of energy in the reaction, calculate speed of emitted alpha particle. Take mass of alpha particle to be 6.68xx10^(-27)kg .

The number of silicon atoms per m^3 is 5 xx 10^28 . This is doped simultaneously with 5 xx10^22 atoms per m^3 of Arsenic and 5xx 10^20 per m^3 atoms of Indium. Calculate the number of lectrons and holes. Given that n_i = 1.5xx 10^16 m . Is the material n-type or p-type?