Answer:
[tex]7.53\cdot 10^{20}[/tex]
Explanation:
First of all, we need to calculate the energy of one photon with wavelength 600 nm. The energy of each photon is given by
[tex]E=\frac{hc}{\lambda}[/tex]
where
[tex]h=6.63\cdot 10^{-34} Js[/tex] is the Planck's constant
[tex]c=3\cdot 10^8 m/s[/tex] is the speed of light
[tex]\lambda=600 nm=6\cdot 10^{-7} m[/tex] is the wavelength of the light
Substituting numbers into the formula, we find
[tex]E_1=\frac{(6.63\cdot 10^{-34}Js)(3\cdot 10^8 m/s)}{6\cdot 10^{-7} m}=3.32\cdot 10^{-19} J[/tex]
Now to find the number of photons, we simply divide the total energy (250 J) by the energy of one photon:
[tex]n=\frac{E}{E_1}=\frac{250 J}{3.32\cdot 10^{-19} J}=7.53\cdot 10^{20}[/tex]
