Answer
A typical virus is a packet of protein and DNA (or
RNA) and can be spherical in shape. The influenza A
virus is a spherical virus that has a diameter of 85 nm.
If the volume of saliva coughed onto you by your friend
with the flu is 0.010 cm 3 and 10 − 9 of that volume consists
of viral particles, how many influenza viruses have
just landed on you?
Answer: 3,2 \cdot 10^4 Infl. A viruses.
Work Step by Step
The volume of a sphere can be calculated by the formula
$V = \frac{4}{3} \pi r^3 $
The radius of a virus is r = 42,5 nm. So the calculated volume of a virus is
$V_V = 321.555,09 = 3.21 \cdot 10^5 nm^3. $
The volume of viruses in the saliva is $V_S = 0,01 * 10^{-9} cm^3$. The convertion factor to nm^3 is of 10^21, so the number of calculated viruses is
$N_V = \frac{V_S}{V_V} = \frac{10^{10}nm^3}{3,215 \cdot 10^5} = 0,32 \cdot 10^5= 3,2 \cdot 10^4$ inlfuenza A viruses.
