Chapter 14/25 Chapter 14/25

Electromagnetic WavesElectromagnetic Waves

The The Electromagnetic SpectrumElectromagnetic Spectrum

Figure 25-3Figure 25-3The Right-Hand Rule Applied to an The Right-Hand Rule Applied to an Electromagnetic WaveElectromagnetic Wave

Figure 25-1Figure 25-1AllAll Accelerating Charges Radiate Accelerating Charges Radiate

Electromagnetic WavesElectromagnetic Waves

Receiving Radio Waves - Receiving Radio Waves - ResonanceResonance

Maxwell - Electromagnetic Maxwell - Electromagnetic waveswaves

All electromagnet waves travel All electromagnet waves travel at the speed of light in a at the speed of light in a

vacuumvacuum

Roses are Red, Violets are VioletRoses are Red, Violets are Violet

1 nanometer = 10 -9 metersEx: 600 nm = 6.00 x 10-7m

What is the speed of Light?What is the speed of Light?

Speed of LightSpeed of Light

• The speed of light can be defined as the The speed of light can be defined as the speed it takes light to travel one meter speed it takes light to travel one meter in 1/299,792,458 of a second.in 1/299,792,458 of a second.

• Presently, the speed of light has a fixed Presently, the speed of light has a fixed value of 299,792,458 m/s. or……..value of 299,792,458 m/s. or……..

• c = 3.00 × 10c = 3.00 × 1088 m/s;  m/s; c = f c = f λλ

• Who measured the Who measured the speed of lightspeed of light? ?

c=f c=f λλ or v=f or v=f λλ

• A cell phone transmits at a A cell phone transmits at a frequency of frequency of 1.33 x 101.33 x 1088 Hz. What is the Hz. What is the wavelength of the electromagnetic wavelength of the electromagnetic wave used by this phone? wave used by this phone?

• c = f c = f λλ• 3.00 × 103.00 × 1088 m/s = 1.33 x 10 m/s = 1.33 x 1088 Hz Hz ( (λλ))• λλ = 2.26 m = 2.26 m

GalileoGalileoOne of the first attempts to measure the speed of light. What do you think he discovered?

Conclusion: Light was really fast!!!!

Romer: Using the moons of Jupiter Romer: Using the moons of Jupiter to Determine the Speed of Lightto Determine the Speed of Light

c=f c=f λλ• A television is tuned to a station A television is tuned to a station

broadcasting at a frequency of 7.30 x 10broadcasting at a frequency of 7.30 x 1077 Hz. For best reception, the rabbit-ear Hz. For best reception, the rabbit-ear antenna used by the TV should be adjusted antenna used by the TV should be adjusted to have a tip-to-tip length equal to to have a tip-to-tip length equal to one-third a wavelength of the broadcast one-third a wavelength of the broadcast signal. Find the optimum length of the signal. Find the optimum length of the antenna.antenna.

• c = f c = f λλ• 3.00 × 103.00 × 1088 m/s = 7.30 x 10 m/s = 7.30 x 1077 Hz Hz ( (λλ))• λλ = 4.11 m = 4.11 m• So, 4.11/3 = 1.37 mSo, 4.11/3 = 1.37 m

Speed of Light Speed of Light

Albert MichelsonAlbert Michelson

Figure 25-7Figure 25-7Fizeau’s Experiment to Determine the Speed of LightFizeau’s Experiment to Determine the Speed of Light

Doppler RadarDoppler Radar

MicrowavesMicrowaves

• A microwave oven produces A microwave oven produces electromagetic waves with a electromagetic waves with a wavelength of about 12 cm. What wavelength of about 12 cm. What are the frequency of such waves? are the frequency of such waves?

• c = f c = f λλ• 3.00 × 103.00 × 1088 m/s = (f) 0.12 m m/s = (f) 0.12 m• λλ = 2.26 m = 2.26 m

Doppler: Red Shift / Blue ShiftDoppler: Red Shift / Blue Shift

Which part of the Galaxy above will produce a Red Shift and Which part will produce a Blue Shift?

Top Blue, Middle Red, Bottom Red