1.

An electric bulb of volume 250cc was sealed during manufacturing at a pressure of `10^(-3)`mm of mercury at `27^(@)`C. Compute the number of air molecules contained in the bulb.Avogadro constant `=6xx10^(23)mol^(-1),` density of mercury`=13600kgm^(-3)and g=10ms^(-2)`.

Answer» `V=250cc =250 xx 10^-3. l`
` P=(10^-3mm)= (10^-3 xx 10^-3 m)`
` =(10^-6 xx 13600 xx 10)`
` 136 xx 10^-3 pascal `
` T= 27^@C = 300 K `
` n=(PV)/(RT)`
` = (136 xx 10^-3 xx 250 xx 10^-3)/ (8.3 xx 300) `
` = (136 xx 250 xx 10^-6)/ (8.3 xx 300)`
No. of molecules
`=((136 xx 250)/(8.3 xx 300)) xx 10^-6 xx 6 xx 10^23`
` = 81 xx 10^17 = 0.81 xx 10^16`


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