Find
the number of photons wmitted er minute by 60 W lamp of moochromatic light of wavelength `5,000 overset @A`.

Explanation

`lambda = 5000 Å = 5000 xx 10^(-10) m = 5 xx 10^(-7) m`
Power of lamp = P = 60 Watt.
Time = t = 1 min = 60 s
Total energy emitted by lamp = Pt
`= 60 xx 60 = 3600 J`
`= (3600)/(1.6 xx 10^(-19)) eV`
` = 3.6/1.6 xx 10^(22) eV`
`= 2.25 xx 10^22 eV`
Energy of incident radiation = `hv = (hc)/(lambda)`
`= (6.62 xx 10^(-34) xx 3 xx 10^8)/(5 xx 10^(-7))`
`= (19.86)/(5) xx 10^(-34 + 8 + 7)`
`= 3.972 xx 10^(-19) J`
`= (3.972 xx 10^(-19))/(1.6 xx 10^(-19)) eV`
`= 2.48 eV`
Number of photoelectrons emitted per minute = `("Total energy minute")/("Energy of one photon") `
`= (2.25 xx 10^22)/(2.48)`
`= 0.907 xx 10^22 eV = 9.07 xx 10^21 eV`