A laser used to read CDs emits red light of wavelength 700 nm. How many photons does it emit in each second if its power is 1.0 W ?
Text Solution
Verified by ExpertsD
Use the Planck's expression to get the energy of 1 photon
is the frequency,
is the Planck constant 
Since, we are given the wavelength 
this expression becomes
where, 
is the speed of light which will take be 
1 watt is 1 Joule of work done per second.
0.1 J of work is being done in 1 second.
So, 
is produced from 1 photon.
is produced from 
photons
is produced from 
photons are emitted in 1 second if its power is 1.0 watt.
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