A 25 watt bulb emits monochromatic yellow light of wavelength of 0.57`mum`. Calculate the rate of emissionn of quanta per second.

Explanation

Energy emitted by the bulb`=25`watt`=25J*s^(-1)`
Energy of a photon `(E)=hv=h(c)/(lamda)`
`lamda=0.57mum=0.57xx10^(-6)m,c=3xx10^(8)m*s^(-1),h=6.626xx10^(-34)J*s`
Substituting the values we get,
`E=((6.626xx10^(-34)J*s)(3xx10^(8)m*s^(-1)))/(0.57xx10^(-6)m)=3.49xx10^(-19)J`
`therefore`No. of quanta emitted`=(25J*s^(-1))/(3.49xx10^(-19)J)=7.16xx10^(19)s^(-1)`