Some properties of electromagnetic waves

Exercise 7.1. How many wavelengths of green light, with a frequency of 5.7 X 10 s , are there in I m  

From the viewpoint of its particle character, the energy of an em wave is absorbed, emitted, or converted into other forms of energy in discrete units (or quanta) called photons. The amount of energy (W) associated with one photon of radiation is 

the amount of energy in a photon of em radiation is inversely proportional to the wavelength and directly proportional to the wave number of the radiation. 

In photochemistry we are often interested in an Avogadro s number (Na = 6.022x 10 ) of photons, which could be considered as 1 mole of photons this is called an einstein. One einstein of photons has energy 

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Some properties of electromagnetic waves depend on frequency. For example, some wavelengths are visible. Some can penetrate and heat materials, including human tissue. Some properties apply across the spectmm. For example, energy from a radiation source diminishes with the square of the distance from the source. Compared to one unit from a source, the energy level at two units away will be one fourth. 

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