# modern physics

#### physics21

Q).Consider two light source of wavelength lambda1(lam1) and lambda2(lam2).
(lam1>lam2) which are emitting n1 and n2 photons respectively,in a given time.
Assume equal power for both the sources, then:

n1>n2 or n2>n1 or n1=n2??

please anyone help me solving this and explaning too!(Smile)

thnk u

#### physics21

I think it should be n1<n2.....but the answer given in book is n1>n2....

#### ChipB

PHF Helper
Your text book should have provided you with the formula for the energy of a photon:

E = hc/lambda

So if lambda1 > lambda2, that means the energy of photon 1 is less than that of photon 2. Hence it takes more photons of wavelength lamda1 to equal the power of lamda2. Therefore: n1 > n2

physics21

thanks a lot!