Question

6. Polarization: What does it mean for light to be polarized? As light passes through a polarized material the filter will reduce the smount of light transmitted as well as set a new angle of polarization for the emerging light. Write down the equa the amount of light transmitted by a filter. 1dentify what each term in this equation represents. tion used to find Example: Unpolarized light strikes the polarizer shown. Determine the amount of light (percemd) that emerges from the filter. Describe 2 applications of polarized filters

Answer 1

Polarization is the property of wave that can oscillate with more than one orientation. A light wave that is vibrating in more than one plane is referred to as unpolarised light.

The process of transforming unpolarized light into polarized light is known as polarization of light.

Polaroid Polarized wave Non-polarized wave

Depending on the orientation of the electric field, polarized light can be divided into three types-

• Linear polarization.
• Circular polarization.
• Elliptical polarization.

Linear polarization- When an ordinary(unpolarized)light is reflected from a polished surface or transmission through certain materials, the electric fields vector oscillates along a straight line in one plane, and the light is said to be linearly polarized.

Horizontally Polarized Light Horizontal Polarizer LINEAR POLARIZED LIGHT Vertically Polarized Light V POLARIZERS UNPOLARIZED LIGHT Vertical Polarizer

Circular polarization- The electric field of light consists of two linear components that are perpendicular to each other, equal in amplitude, but have a phase difference of π/2. The resulting electric field rotates in a circle around the direction of propagation and, depending on the rotation direction, is called left- or right-hand circularly polarized light.

Elliptical polarization- The electric field of light describes an ellipse. This results from the combination of two linear components with differing amplitudes or a phase difference that is not π/2. This is the most general description of polarized light, and circular and linear polarized light can be viewed as special cases of elliptically polarized light.

Malus' law Suppose we have a second piece of Polaroid whose transmission axis makes an angle θ with that of the first one. The E vector of the light between the Polaroids can be resolved into two components, one parallel and one perpendicular to the transmission axis of the second Polaroid (see Figure 1). If we call the direction of transmission of the second Polaroid y, Only the second, y' component is transmitted by the second Polaroid. The intensity of light is proportional to the square of the electric field amplitude. Thus the intensity transmitted by both Polaroids can be expressed as cOS y' If Io E2 is the intensity between the two Polaroids, the intensity transmitted by both of them would be: : 10 cos2 θ I (θ) This equation is known as Malus Law after its discoverer, E.L. Malus (1775-1812). It applies to any two polarizing elements whose transmission directions make an angle θ with each other.

first is called polarizer and the second is called analyzer. As you will see, no light reaches the photocell when the polarizer and analyzer are crossed (θ 90°). Transmission axis Transmission axis Unpolarized light Photodiode Polarizer /' Analyzer Ey Ex

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