How many photons having wavelength `4557 Å` are needed to provide 1 Joule of energy ?

Explanation

Energy, `E=(nhc)/(lambda) or n=(E lambda)/(hc) =(1J xx 4557 xx 10^(-10)m)/(6.626 xx 10^(-34)J s xx 3.0 xx 10^(8)ms^(-1)) =2.92 xx 10^(18)` photons