November 18, 2013

Electromagnetic Radiation

Objectives At the end of class, you will be able to: List the forms of electromagnetic radiation Find wavelength or frequency of electromagnetic radiation

Waves and Particles Particles are solid matter Waves are movement in matter, like an ocean wave or a wave at a football game

Electromagnetic Radiation Energy that travels through space as a wave EXAMPLES: Gamma rays X-rays Ultraviolet rays Visible light Infrared Microwaves Radiowaves Electromagnetic spectrum

In a vacuum all electromagnetic radiation travels at the speed of light. This speed is c = 3.0 × 10 8 m/s

Wavelength Symbol: λ (lambda) Units: m (meter) Distance between corresponding points on a wave

Frequency Symbol: ν (nu) Units: s -1, Hz, 1/s Number of waves that pass a point per second

Each form of light has different wavelength and frequency, but they all have the SAME SPEED

As wavelength ______________, frequency _______________. As wavelength ______________, frequency ________________. increases decreases increases

The big equation for EM radiation: c = λν

PRACTICE: 1. What is the wavelength of electromagnetic radiation with a frequency of 2.0 × Hz? Where is this in the electromagnetic spectrum? If it is visible light, what color is the light? Use formula: c = λν Identify known information: c = 3.0 x 10 8 m/s ν = 2.0 × Hz Plug known information into formula: 3.0 x 10 8 m/s = λ( 2.0 × Hz) Solve for λ λ = (3.0 x 10 8 m/s)/ ( 2.0 × Hz) λ = 1.5 × m

Ultraviolet light

PRACTICE: 2. What is the frequency of light with a wavelength of 4.5 × m? Where is this in the electromagnetic spectrum? If it is visible light, what color is the light? Use formula: c = λν Identify known information: c = 3.0 x 10 8 m/s λ = 4.5 × m Plug known information into formula: 3.0 x 10 8 m/s = (4.5 × m) ν Solve for ν ν = (3.0 x 10 8 m/s)/ ( 4.5 × m) ν = 6.67 × Hz

Visible light – Blue

PRACTICE: 3. What is the wavelength of electromagnetic radiation with a frequency of 5.85 × Hz? Where is this in the electromagnetic spectrum? If it is visible light, what color is the light? Use formula: c = λν Identify known information: c= 3.0 x 10 8 m/sv = 5.85 x Hz Plug known information into formula: 3.0 x 10 8 m/s = λ (5.85 x s -1 ) Solve for ν ν = (3.0 x 10 8 m/s)/(5.85 x s -1 ) = ν = 5.13 x m

Gamma Rays (or X-rays) – The wavelengths overlap sometimes

PRACTICE: 4. What is the frequency of light with a wavelength of 64 cm? Where is this in the electromagnetic spectrum? If it is visible light, what color is the light? Hint: make sure all variables are in units of m! 64 cm | 1m = 0.64 m 100 cm

PRACTICE: 4. What is the frequency of light with a wavelength of 0.64 m? Where is this in the electromagnetic spectrum? If it is visible light, what color is the light? Use formula: c = λν Identify known information: c= 3.0 x 10 8 m/s λ = 0.64 m Plug known information into formula: 3.0 x 10 8 m/s = (0.64m) ν Solve for ν ν = ( 3.0 x 10 8 m/s)/(0.64 m) = ν = 4.69 x 10 8 Hz

Radio Waves

Check: What is wavelength? What is the unit for wavelength? What is frequency? What is the unit for frequency? How can you find one if you know the other?