A photon of wavelength 250 nm, absorbed by a substance was subsequently emitted as two photons. The first photon had a wavelength of 600 nm. What was the wavelength of the second photon?

Explanation

Energy of absorbed photon, `E=hc//lamda`
  Energy of first photon emitted, `E_(1)=hc//lamda_(1)`, Energy of second photon emitted, `E_(2)=hc//lamda_(2)`
`E=E_(1) +E_(2)" or "(1)/(lamda)=(lamda) =(1)/(lamda_(1))+(1)/(lamda_(2)) and (1)/(lamda_(2)) =(1)/(lamda_(1))-(1)/(lamda_(1))" i.e. "(1)/(lamda_(2))=(1)/(250) -(1)/(600)`
 Wavelength of second photon emitted, `lamda_(2)=(250xx600)/(600-250)=428.57` nm.