Physical Science 9���Chapter 13: Electromagnetic

Waves ���Chapter 14: Light���

Chapter 15: Mirrors and Lenses

Section 13.1: …Electromagnetic Waves Section 13.2: The Electromagnetic Spectrum

Electromagnetic Waves --Electromagnetic waves consist of electric!

and magnetic fields vibrating at right angles!to each other.!

--Electromagnetic waves are produced by!vibrating electric charges.!

--Electromagnetic waves used in radio and!TV broadcasts are produced by electric!currents produced in the antennas.!

--See animation of electromagnetic waves.!(HP 06, Ch 13, 70120html)!

Speed of Electromagnetic Waves --Electromagnetic waves can travel through!

a vacuum at a speed of 3.0 x 108 m/s!(186,000 mi/sec). !

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c = f ∗λorc = ν *λ

--The speed of electromagnetic waves is given by:!

--Light travels from the Sun to the Earth in!about 8 1/3 minutes.!

--Light can travel about 7 1/2 times around!the Earth in one second!!!!

--According to Einstein’s Theories of Relativity,!nothing can travel faster than light; the speed!of light is the ultimate speed limit in the!universe.!

The Electromagnetic Spectrum --The electromagnetic spectrum consists of!1. radio waves! 2. microwaves!

3. infrared waves! 4. visible light waves!

5. ultraviolet waves! 6. x-rays!

7. gamma rays!

--The parts of the electromagnetic spectrum!vary in their frequency, wavelength, and energy.!

--Electromagnetic waves with a short wavelength!have a high frequency and a high energy.!

Examples: x-rays and gamma rays!

--Electromagnetic waves with a long wavelength!have a low frequency and a low energy.!

Example: radio waves!

The Electromagnetic Spectrum

The Electromagnetic Spectrum

Calculations with the Speed of Light

Example: What is the speed of light in a vacuum!if a wave with a frequency of 700 nm has a!frequency of 4.3 x 1014 Hz?!

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λ = 700 nm x 1 m109 nm

= 7.0 x 10-7 m

or

λ = 700 nm x 10-9 m1 nm

= 7.0 x 10-7 m

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c = f × λ

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c = (4.3 x 1014 Hz) × (7.0 × 10-7 m)

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c = 3.01 x 108 ms

Example 2: What is the wavelength of a radio!wave whose frequency is 1.0 x 108 Hz?!

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c = f x λ

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λ = cf

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λ = 3.0 x 108 m

s1.0 x 108 Hz

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λ = 3.0 m