What is Polarization of Light?

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Grade Level:

Class 12

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Definition

What is it?

Polarization of light is when the vibrations of light waves are restricted to a single plane. Normally, light vibrates in all directions perpendicular to its path, but after polarization, it vibrates in only one specific direction.

Simple Example

Quick Example

Imagine a rope tied to a wall. If you shake it up and down, left and right, and diagonally, that's like unpolarized light. Now, if you pass the rope through a vertical fence, it can only vibrate up and down. That's like polarized light – its vibrations are restricted.

Worked Example

Step-by-Step

Let's say you have unpolarized light passing through a polarizing filter. The intensity of the unpolarized light is I0.

Step 1: Unpolarized light with intensity I0 passes through the first polarizer. According to Malus's Law, the intensity of light after passing through the first polarizer is I1 = I0 / 2.
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Step 2: Now, this polarized light (I1) passes through a second polarizer, called an analyzer. The axis of the analyzer is at an angle of 30 degrees to the axis of the first polarizer.
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Step 3: We need to find the intensity of light coming out of the second polarizer. We use Malus's Law again: I2 = I1 * cos^2(theta), where theta is the angle between the two polarizers.
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Step 4: Substitute the values: I2 = (I0 / 2) * cos^2(30 degrees).
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Step 5: We know cos(30 degrees) = sqrt(3) / 2. So, cos^2(30 degrees) = (sqrt(3) / 2)^2 = 3 / 4.
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Step 6: Calculate I2 = (I0 / 2) * (3 / 4) = 3 * I0 / 8.
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Answer: The intensity of light coming out of the second polarizer is 3 * I0 / 8.

Why It Matters

Understanding polarization helps engineers design better displays for phones and TVs, and it's key in developing advanced medical imaging tools. From making your phone screen clear to helping doctors see inside the body, polarization is a fundamental concept used by scientists and innovators.

Common Mistakes

MISTAKE: Thinking polarization completely blocks light | CORRECTION: Polarization doesn't block light entirely; it just restricts the direction of its vibrations. Some light always passes through, unless the polarizers are crossed at 90 degrees.

MISTAKE: Confusing polarization with reflection or refraction | CORRECTION: Polarization is about the orientation of light wave vibrations, while reflection is bouncing off a surface and refraction is bending when passing through a medium.

MISTAKE: Believing all light can be polarized | CORRECTION: Only transverse waves (like light) can be polarized because their vibrations are perpendicular to the direction of travel. Longitudinal waves (like sound) cannot be polarized.

Practice Questions

Try It Yourself

QUESTION: If unpolarized light with an intensity of 100 units passes through an ideal polarizer, what is the intensity of the light after passing through it? | ANSWER: 50 units

QUESTION: Light from a polarizer has an intensity of 80 units. It then passes through a second polarizer whose axis is oriented at 60 degrees to the first. What is the intensity of the light after the second polarizer? (Hint: cos(60 degrees) = 0.5) | ANSWER: 80 * cos^2(60) = 80 * (0.5)^2 = 80 * 0.25 = 20 units

QUESTION: Unpolarized light with intensity I0 passes through two polarizers. The first polarizer's axis is vertical. The second polarizer's axis is horizontal. What is the final intensity of the light? | ANSWER: 0. After the first polarizer, intensity is I0/2 and light is vertically polarized. The second polarizer is horizontal, so it blocks all vertically polarized light, resulting in 0 intensity.

MCQ

Quick Quiz

What happens to the vibrations of light waves when light is polarized?

They become stronger

They are restricted to a single plane

They disappear completely

They change color

The Correct Answer Is:

Polarization means the oscillations of the light wave are confined to one specific direction, not that they become stronger, disappear, or change color.

Real World Connection

In the Real World

You use polarized light every day! The display on your mobile phone or laptop uses polarized light to create images. Also, polarized sunglasses reduce glare from surfaces like water or roads, making it easier to see while driving or enjoying a day at the beach.

Key Vocabulary

Key Terms

POLARIZER: A filter that allows only light vibrating in a specific plane to pass through | UNPOLARIZED LIGHT: Light whose vibrations occur in all possible directions perpendicular to the direction of wave travel | POLARIZED LIGHT: Light whose vibrations are restricted to a single plane | MALUS'S LAW: A law that quantifies the intensity of light transmitted through a polarizer when polarized light is incident upon it | TRANSVERSE WAVE: A wave in which the particles of the medium oscillate perpendicular to the direction of wave propagation.

What's Next

What to Learn Next

Next, you can explore 'Brewster's Law' and 'Double Refraction'. These concepts build on polarization to explain how light behaves when it reflects off surfaces or passes through certain crystals, which is super useful for making advanced optical instruments!