A100 watt bulb emits monochromatic light of wavelength 400 nm. calculate the number of photons emitted per second by the bulb.

f = 7.5 E14 s-1

Explanation:

energy emitted by photon:

∴ λ = (400nm)(m/1 E9 nm) = 4.00 E-7 m

∴ h ( Planck's constant) = 6.626070150 E-34 J.s

∴ c (velocity of light) = 3.00 E8 m/s

∴ f (frequency): photon/s

If (1) = (2):

⇒ f = c / λ = E / h

⇒ f = (3.0 E8 m/s) / ( 4.00 E-7 m) = 7.5 E14 s-1

the answer is na (sodium)