The power of the flash is [tex]2.36 * 10^{-9} W[/tex].
First we calculate the energy of a single photon; i.e.
[tex]E_{1} = hc/\alpha[/tex]
where, h = planck's constant = [tex]6.63 * 10^{-34} Js[/tex]
c = speed of light = [tex]3 * 10^{8} m/s[/tex]
[tex]\alpha[/tex] = wavelength = 490 nm = [tex]4.9 * 10^{-7} m[/tex]
Putting these values in equation, we get
[tex]E_{1} = 4.05 * 10^{-19} J[/tex]
Total energy is given by, E=Pt
where, P = power and t= time
Now number of photons is given by : N = E/[tex]E_{1}[/tex]
⇒ [tex]NE_{1} = E[/tex]
⇒ [tex]NE_{1} /t = P[/tex]
Given, N = [tex]1.4*10^{10}[/tex] and t = 2.4 s
Putting these values in above equation we get P = [tex]2.36 * 10^{-9} W[/tex]
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