Advertisements
Advertisements
Question
A strong current of trivalent gaseous boron passed through a silicon crystal decreases the density of the crystal due to part replacement of silicon by boron and due to interstitial vacancies created by missing Si atoms. In one such experiment, one gram of silicon is taken and the boron atoms are found to be 1000 ppm by weight, when the density of the Si crystal decreases by 12%. The percentage of missing vacancies due to silicon, which are filled up by boron atoms will be ____ g. [Given · Atomic wt. Si= 30, B = 11]
Options
3
7
5
2
Solution
A strong current of trivalent gaseous boron passed through a silicon crystal decreases the density of the crystal due to part replacement of silicon by boron and due to interstitial vacancies created by missing Si atoms. In one such experiment, one gram of silicon is taken and the boron atoms are found to be 1000 ppm by weight, when the density of the Si crystal decreases by 12%. The percentage of missing vacancies due to silicon, which are filled up by boron atoms will be 2 g.
Explanation:
`1000 = w_"B"/1 xx 10^6`
`w_"B" = 10^-3` gm
`1 - w_("Si") + w_"B" = 0.88` gm
`1 - w_"Si" + 0.001` = 0.88
`w_"Si" = 1.001 - 0.88`
`w_"Si"` = 0.121 gm
`10^(-3)/10 xx 30/0.121 xx 100 = 2.47 ~~ 2`
