A 100-watt light bulb radiates energy at a rate of 100 J/s. (The watt, a unit of

Question

A 100-watt light bulb radiates energy at a rate of 100 J/s. (The watt, a unit of power or energy over time, is defined as 1 J/s.) If all of the light emitted has a wavelength of 525 nm, how many photons are emitted per second? Express your answer to three significant figures. radiation = 3.78 middot 10^-24 Part B The energy required to dislodge electrons from sodium metal via the photoelectric effect is 275 kJ/mol. What wavelength of light in nanometers has sufficient energy per photon to dislodge an electron from the surface of sodium? Express the wavelength in nanometers to three significant figures.

Explanation / Answer

basis = 1 second

Etotal = 100 J

WL = 525 nm = 525*10^-9 m

Eparticle = hc/WL

so..

h = Planck Constant = 6.626*10^-34 J s

c = speed of particle (i.e. light) = 3*10^8 m/s

Eparticle = energy per particle J/photon

substitute

Eparticle = hc/WL = ( 6.626*10^-34)(3*10^8)/(525*10^-9 ) = 3.786285*10^-19 J

so..

Total energy is 100 J

particles = Etotal / Eparticle = (100)/(3.786285*10^-19) = 2.6411*10^20 particles per second

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