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Home , Polarization (waves)

LECTURE 11 ELECTROMAGNETIC &

Instructor: Kazumi Tolich Lecture 11

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¨ 25.5 Electromagnetic waves ¤ Induced fields ¤ Properties of electromagnetic waves ¤ Polarization ¤ Energy of electromagnetic waves ¤ and changing polarization

¨ 17.1 What is ? ¤ Propagation of light waves ¤ Light is an electromagnetic ¤ The index of refraction 25.5 Induced fields

¨ A changing creates an induced , and a changing electric field creates an induced magnetic field.

¨ Electric and magnetic fields can sustain themselves free of charges and currents in the form of an electromagnetic wave. Quiz: 25.5-1

4 25.5 Properties of electromagnetic waves & 17.1 Light is an electromagnetic wave

¨ Electromagnetic waves of all frequencies, �, and wavelengths, �, including light, propagate through a at the same speed:

1 � = �� = = 3.0 × 10 m⁄s ��

¨ The amplitudes of the fields in an electromagnetic wave are related:

� = � � 25.5 Polarization

¨ The contains the electric field vectors of an electromagnetic wave.

¨ Radiation emitted from randomly moving atoms is unpolarized. 25.5 Energy of electromagnetic waves

¨ The energy of the electromagnetic wave depends on the amplitudes of the electric and magnetic fields.

¨ of electromagnetic wave is given by

� 1 1 � � = = ��� = � � 2 2 � Example: 25.5-1 (Knight P25.27)

A oven operates at 2.4 GHz with an intensity inside the oven of 2500W/m2. What are the amplitudes of the oscillating electric and magnetic fields? Quiz: 25.5-2

9 25.5 Polarizers and changing polarization / Demo

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¨ A will transmit the component of light in the polarizer axis direction.

¨ The intensity of the transmitted beam is given by Malus’s law: �

� � = � cos �

¨ Demo: sheets � 25.5 Polarizers and changing polarization - applications / Demo

¨ Different material change the polarization of light in different ways.

¨ LCDs use liquid , whose polarization axis can be rotated depending on the voltage across them.

¨ Many organic compounds such as rotate the polarization direction depending on its concentration.

¨ In polarizing with vertical polarization axis cuts horizontally polarized glare from horizontal surfaces.

¨ 3D movie .

¨ Stressed material acts like polarizers. ¤ Demo: Polarization by stress in Quiz: 25.5-3 For fun: Polarization by

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¨ Unpolarized light can be partially or completely polarized by scattering from atoms or molecules, which act as small antennas. 17.1 What is light?

¨ Each of the three models of light successfully explains the behavior of light within a certain domain. ¤ The wave model: Under many circumstances, light exhibits the same behavior as or water waves. and electro-optical devices are best understood in terms of the wave model of light. The study of light as a wave is called wave . ¤ The model: The properties of , mirrors, lenses, and optical instruments such as telescopes and are best understood in terms of straight-line paths of light rays called ray optics. ¤ The model: In the quantum world, light consists of , the quanta of light, that have both wave-like and particle-like properties. Photons are. 17.1 The propagation of light waves / Demo

¨ The wave spreads out (diffracts) to fill the space behind the opening when the opening is comparable in size to the wavelength of the wave.

¨ When the opening is many times larger than the wavelength of the wave, the wave continues to move straight forward, similar to the straight-line appearance of light with sharp shadows as light passes through large windows.

¨ Demo: Ripple tank diffraction 17.1 The index of refraction

¨ The in a material is characterized by the material’s index of refraction �, defined by

speed of light in vacuum � � = = speed of light in the material � Quiz: 17.1-1