Question

A sodium vapor street lamp emits yellow light at wavelength 589nm. How much energy is released if a mole of photons are emitted?

Answer 1

Answer - We are given, wavelength, l = 589 nm

First need to calculate the energy for one photon and we know the relationship

E = h*v

   = h*C / l

We need to convert given wavelength from nm to m

1 nm = 1*10^-9 m

So, 589 nm = ? m

= 5.89*10^-7 m

So, E = 6.626*10^-34 J.s * 3*10⁸ m.s^-1 / 5.89*10^-7 m

         = 3.37*10^-19 J

Now we know,

1 mole of photon = 6.023*10²³ photon

So, energy is released if a mole of photons are emitted

= 3.37*10^-19 J * 6.023*10²³ photon per mole

= 2.033*10⁵ J.

So, 2.033*10⁵ J energy is released if a mole of photons are emitted