Answer:
2500
Explanation:
1 Angstrom (1 A) corresponds to
[tex]1 A = 10^{-10} m[/tex]
Therefore we can convert the wavelength of the light from Angstroms to meters:
[tex]\lambda = 4000 A = 4000 \cdot 10^{-10} m = 4\cdot 10^{-7} m[/tex]
We also know that
[tex]1 mm = 1\cdot 10^{-3} m[/tex]
So the number of waves in 1 mm of distance is:
[tex]n=\frac{1\cdot 10^{-3} m}{4\cdot 10^{-7} m}=2500[/tex]
