Chapter 6: Electromagnetic Radiation

1. Chapter 6: Electromagnetic Radiation • To understand the electronic structure of atoms, one must understand the nature of electromagnetic radiation. • Light is an example of electromagnetic radiation • Electromagnetic radiation carries energy through space • Includes visible light, dental x-rays, radio waves • All forms of electromagnetic radiation move through a vacuum at the same speed, 3.00 x 108 m/s ("speed of light") • Have "wave-like" characteristics

2. Characteristics of Electromagnetic Radiation • Wavelength ( -lambda): Is the distance from peak to peak or trough to trough of a wave • Measured in m or nm. • Frequency (ν -nu)of the wave is the number of complete wavelengths or cycles that pass a given point each second • Expressed in cycles per second, also known as hertz (Hz). • Usually the dimension 'cycles' is omitted ; unit for frequency is per seconds denoted by s-1 or /sec • Amplitude isthe distance from node to crest or trough • Larger the amplitude, the brighter the light

3. Relationship Between wavelength (λ) and frequency (ν) • Wavelength (λ- lambda) is inversely proportional to frequency (ν- nu). λα 1/ ν • The product of frequency and wavelength of an electromagnetic radiation is its speed c = νλ ν = frequency (s-1) (The unit cycles per second s-1 is also called hertz or Hz) λ = wavelength (m) c = speed of light (ms-1) = 3.00 x 108 ms-1 Memorize this equation

4. Electromagnetic Radiation V I B G Y O R Wavelength (λ) Frequency (γ) Energy (E) Memorize the order of different types of radiation with respect to E, λ, γ

5. Example: Relationship Between λ and ν • Electromagnetic radiation with a wavelength of 532 nm is green light. Calculate its frequency in hertz. (Ans: 5.64 x 1014s-1 or Hz) • Photosynthesis uses light with a frequency of 4.54 x 1014 s-1. What wavelength does this correspond to in nm? (Ans: 661 nm)