© John Erickson, 2005 WS5-2PlancksEq E = h × h = 6.63 × 10-34 J·s useful equations c = × c = 3.00 × 108 m/s 1 m = 1 × 109 nm 1 kJ = 1000 J example Light with a wavelength of 525 nm is green. Calculate the energy in joules for a green light photon. - find the frequency: υλ×=c λcv = nmmnmsmv981011525/1000.3×××= sv /11071.514×= - find the energy: υ×=hE )/11071.5)(10626.6(1434ssJE ×⋅×=− photonJE /1078.319−×= Problem-Solving Strategy Known Unknown Frequency ( ) Energy (E) Wavelength () Frequency ( ) Energy (E) Energy (E) Frequency ( ) Wavelength () Max Planck theorized that energy was transferred in chunks known as quanta, equal to h. The variable h is a constant equal to 6.63 × 10-34 J·s and the variable represents the frequency in 1/s. This equation allows us to calculate the energy of photons, given their frequency. If the wavelength is given, the energy can be determined by first using the wave equation (c = × ) to find the frequency, then using Planck’s equation to calculate energy. Use the equations above to answer the following questions. 1. Ultraviolet radiation has a frequency of 6.8 × 1015 1/s. Calculate the energy, in joules, of the photon. 2. Find the energy, in joules per photon, of microwave radiation with a frequency of 7.91 × 1010 1/s. 3. A sodium vapor lamp emits light photons with a wavelength of 5.89 × 10-7 m. What is the energy of these photons? 4. One of the electron transitions in a hydrogen atom produces infrared light with a wavelength of 7.464 × 10-6 m. What amount of energy causes this transition? 5. Find the energy in kJ for an x-ray photon with a frequency of 2.4 × 1018 1/s. 6. A ruby laser produces red light that has a wavelength of 500 nm. Calculate its energy in joules. 7. What is the frequency of UV light that has an energy of 2.39 × 10-18 J? 8. What is the wavelength and frequency of photons with an energy of 1.4 × 10-21 J? Name ________________ Planck’s Equation Chem Worksheet 5-2 λνc= νhE= hE=ν νhE=
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