Part A A 100-watt lightbulb radiates energy at a rate of 100 J/s (The watt, a un

Question

Part A A 100-watt lightbulb 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. Part B The energy required to dislodge electrons from sodium metal via the photoelectric effect is 275 kJ/mol. What wavelength in nm of light has sufficient energy per photon to dislodge an electron from the surface of sodium? Express the wavelength in nanometers to three significant figures. Part A A 100-watt lightbulb 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. Part B The energy required to dislodge electrons from sodium metal via the photoelectric effect is 275 kJ/mol. What wavelength in nm of light has sufficient energy per photon to dislodge an electron from the surface of sodium? Express the wavelength in nanometers to three significant figures. Part B The energy required to dislodge electrons from sodium metal via the photoelectric effect is 275 kJ/mol. What wavelength in nm of light 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

energy of one photon at 525 nm

= E = hv/lambda
= (6.63 x 10 -34 J.s) (3.00 x 10 8m/s) / (5.25 x 10 -7 m)
= 3.789 x 10 -19 J


number of photons to reach 100 J/s

= rate = (energy/s) / (energy/photon)
= (100 J/s) / (3.789 x 10-19 J/photon)
= 2.6395 x 10 20 photons/s

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