## Chemistry: The Central Science (13th Edition)

The number of photons per second is emitted by the laser: $8.073\times10^{16}photons/s$.
*Strategy: 1) Calculate the energy of a photon of this radiation. 2) Find out how much energy is absorbed per second by the detector. 3) Calculate the number of photons emitted by the laser per second. 1) Calculate the energy of a photon of this radiation. *Known variables and constants: - Wavelength of radiation: $\lambda=9.87\times10^{-7}m$ - Planck's constant: $h\approx6.626\times10^{-34}J.s$ - Speed of light in a vacuum: $c\approx2.998\times10^8m/s$ *The energy of a photon of this radiation is: $E_p=\frac{h\times c}{\lambda}=\frac{(6.626\times10^{-34})\times(2.998\times10^8)}{9.87\times10^{-7}}\approx2.013\times10^{-19}J/photons$ 2) Find out how much energy is absorbed by the detector per second. *Known variables: - Total energy absorbed: $E=0.52J$ - Amount of time: $t=32s$ *The amount of energy absorbed per second is: $E_s=\frac{E}{t}=\frac{0.52}{32}=1.625\times10^{-2}J/s$ 3) Calculate the number of photons ($N$) emitted by the laser per second. $N=\frac{E_s}{E_p}=\frac{1.625\times10^{-2}}{2.013\times10^{-19}}\approx8.073\times10^{16}photons/s$