X-ray are produced in coolidge tube. It consists of a thick glass bulb evacuated about `10^(-0)` cm of Hg so that no discharge can pass in it. A cathode serves as source of electron is made up of tungsten filament heated by a low voltage current. A cylindrical metal shield S surrounds the filament and is kept at negative potential with respect to the filament is focuses the electron emitted from the filament on the target T. the target is mounted on the surface of a copper block fixed to the end of a copper rod . The rod is fitted with fins with for air cooling or cooled by circulating water A potential difference of about 20.000 V is applied across the tube to acceleration the electrons. The acceleration electrons strike to the target and produces continous and characteristic x-rays.
In the coolidge tube experiment platinum is used as target material for the emission of k-series x-rays. The K,L and M energy level of this element are `7.8 xx 10^4 eV, 1.2 xx 10^4 eV and 3 xx 10^3 eV` respectively `C= 3 xx 10^8 m//s, 1 eV =1.6 xx 10^(-19) and h= 6.23 xx 10^(-34)` j-s. The wavelength of `k_(alpha)` lines will be

Options

A. 0.188 Å
B. 0.376 Å
C. 0.999 Å
D. 0.25 Å

Answer

A