# Number of virus particles

1. Jan 21, 2007

### anf9292

1. The problem statement, all variables and given/known data
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 cm3 and 1/109 of that volume consists of viral particles, how many influenza viruses have just landed on you?

2. Relevant equations
V = 4/3 x pie x r^3

3. The attempt at a solution
I'm thinking that I should take half of 85nm which is 42.5nm and plugging it into the volume formula for a spherical. The volume of the whole spherical virus comes out to be 3.21E-5.

3.21E-5 / 0.010cm^3 = .00321

1/10^9 of .00321 = 3.11E-7 particles?

2. Jan 21, 2007

### Kurdt

Staff Emeritus
Its easier if you use nanometers in the original volume calculation. Secondly you would not divide the virus volume by the saliva volume, you need to do this the other way round. Thirdly I don't know if they want you take the spherical nature of the virus into account and assume spherical saliva which could make a big difference. You'll know what your teacher wants more than me.