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 × 108 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 ________________.

increasesdecreases

decreasesincreases

The big equation for EM radiation:

c = λν

PRACTICE:• 1. What is the wavelength of electromagnetic radiation

with a frequency of 2.0 × 1015 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 108 m/s ν = 2.0 × 1015 Hz• Plug known information into formula:

3.0 x 108 m/s = λ(2.0 × 1015 Hz)• Solve for λ

λ = (3.0 x 108 m/s)/(2.0 × 1015 Hz) λ = 1.5 × 10-7 m

Ultraviolet light

PRACTICE:• 2. What is the frequency of light with a wavelength of

4.5 × 10-7 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 108 m/s λ = 4.5 × 10-7 m• Plug known information into formula:

3.0 x 108 m/s = (4.5 × 10-7 m) ν• Solve for ν

ν = (3.0 x 108 m/s)/(4.5 × 10-7 m) ν = 6.67 × 1014 Hz

Visible light – Blue

Visible light – Blue

PRACTICE:• 3. What is the wavelength of electromagnetic

radiation with a frequency of 5.85 × 1018 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 108 m/s v = 5.85 x 1018 Hz • Plug known information into formula:

3.0 x 108 m/s = λ (5.85 x 1018 s-1)• Solve for ν ν = (3.0 x 108 m/s)/(5.85 x 1018 s-1) = ν = 5.13 x 10-11 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 108 m/s λ = 0.64 m• Plug known information into formula:

3.0 x 108 m/s = (0.64m) ν

• Solve for ν

ν = (3.0 x 108 m/s)/(0.64 m) = ν = 4.69 x 108 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?