A 150 W hollow-cathode lamp of an atomic absorption spectrophotometer emits monochromatic light of wavelength 553.5 nm. Calculate the number of photons emitted in one minute (150 watts `150 Js^(-1)`). 

Explanation

Energy emitted in one minute `= 150 xx 60 J= 9000 J`
Energy of a photon,
`E-hv =(hc)/(lamda) =(6.626xx10^(-34) Js xx3xx10^(8) ms^(-1))/(553.5xx10^(-9) m)=3.59xx10^(-19) J`
  Photons emitted per minute `=("Energy emitted per minute")/("Energy per photon")=(9000 J)/(3.507xx10^(-19) J)=2.59xx10^(22)`