First find the volume:
length = 3.8 um
diameter = 1.6 um
so, radius = 1.6 / 2 = 0.8 um
so, volume = [tex]\pi r^2 l[/tex]
=[tex]3.14 \times 0.8^2 \times 3.8 [/tex]
[tex]Volume= 7.63 um^3[/tex]
1 um = 10^{-6} m
convert volume into m^3
so, [tex]Volume= 7.63 um^3[/tex] = [tex]7.63 \times (10^{-6})^3 = 7.63 \times 10^{-18} m^3 [/tex]
Now, Concentration is always in moles/Litre. So, we need to change the volume to litre.
1 m^3 = 10^{-3} L
So, [tex]7.63 \times 10^{-18} m^3 = 7.63 \times 10^{-18} \times 10^{-3}L = 7.63 \times 10^{-21}L [/tex]
Now, number of moles = concentration x volume
= [tex] 0.0047 \times 7.63 \times 10^{-21}= 3.5 \times 10^{-23} [/tex]
so no. of molecules = [tex] 3.5 \times 10^{-23} \times 6.022 \times 10^{24} = 210 [/tex]
