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Electromagnetic Waves

Presentation Outline Review: Reflection and Refraction “Mechanical” vs. Light waves Electromagnetic Spectrum Frequency, wavelength, and speed of light Energy of light equation (review) Examples of solving EM Radiation Practice Double-Slit Experiment Photoelectric Effect Simulation Wave-Particle Duality

Reflection Reflection occurs when a wave bounces off a surface and remains in the same medium. Light waves obey the law of reflection: the angle of “incidence” equals the angle of reflection.

Refraction Refraction is the bending of a wave as it passes from one medium into another and changes speed. Generally, the speed of light is slower in denser materials. The frequency of a wave does not change, so if the speed decreases, what happens to the wavelength? Faster Slower

Refraction Refraction is the bending of a wave as it passes from one medium into another and changes speed. Generally, the speed of light is slower in denser materials. The frequency of a wave does not change, so if the speed decreases, what happens to the wavelength? MaterialSpeed of Light Vacuum100% Air99.97% Water75% Flint Glass63% Diamond41%

Refraction Refraction is the bending of a wave as it passes from one medium into another and changes speed. Generally, the speed of light is slower in denser materials. The frequency of a wave does not change, so if the speed decreases, what happens to the wavelength?  The wavelength decreases! MaterialSpeed of Light Vacuum100% Air99.97% Water75% Flint Glass63% Diamond41%

Faster Slower Faster Light moves towards the normal. Light moves away from the normal.

What is a light wave? Electromagnetic Radiation

Mechanical Waves vs. Electromagnetic Waves Light is an electromagnetic wave, which carries energy in the form of vibrating electric and magnetic fields. Unlike other waves, electromagnetic waves are capable of transmitting its energy through a vacuum (like empty space). All electromagnetic radiation travels through a vacuum at the same speed: c = 3 x 10 8 m/s. A wave that is not capable of transmitting its energy through a vacuum is called a mechanical wave (for example, a sound wave or stadium wave).

Mechanical Waves vs. Electromagnetic Waves Light is an electromagnetic wave, which carries energy in the form of vibrating electric and magnetic fields. Unlike other waves, electromagnetic waves are capable of transmitting its energy through a vacuum (like empty space). All electromagnetic radiation travels through a vacuum at the same speed: c = 3 x 10 8 m/s. A wave that is not capable of transmitting its energy through a vacuum is called a mechanical wave (for example, a sound wave or stadium wave).

ELECTROMAGNETIC RADIATION SPECTRUM

Increasing Frequency Increasing Wavelength

Increasing Energy Increasing Frequency Increasing Wavelength

Equations Involving Light The speed of light is related to its frequency and wavelength by the same wave equation: v = f λ.  As the frequency of a light wave increases, the wavelength of light decreases.  As the frequency of a light wave decreases, the wavelength of light increases. The energy of light is also related to its frequency and wavelength.  The energy of a light wave is directly proportional to its frequency.  The energy of a light wave is inversely proportional to its wavelength.

Example: A microwave has a wavelength of 10.0 μm. What is the frequency of this wave (assuming it is travelling in a vacuum)? (1 μm = m)

Observations about Light

Light is a Wave and a Particle Light acts like a wave because it reflects and refracts, and also that two light wave interfere with each other. Light’s wave properties can be seen in the Double-Slit Experiment: Light also acts like a particle because of experiments showing that light comes in “packets” of energy known as photons. These particle properties of light can be seen in the photoelectric experiment:

Light is a Wave and Particle Wave-Particle Duality in One Minute: oPJXZw oPJXZw Wave-Particle Duality in 9 Minutes: 5x7svfg 5x7svfg