Problem 19 - 43 Years JEE ADVANCED (1978-2020) + JEE MAIN Chapterwise & Topicwise Solved Papers Chemistry

Question

The polymer used for optical lenses is : [Main Online April 22, 2013] (a) polypropylene (b) polyvinyl chloride (c) polythene (d) polymethyl methacrylate

Step-by-Step Solution

Answer

Polymethyl methacrylate (d) is used for optical lenses.

Step 1: Understand the options

First, read through the given options to identify the different polymers listed: (a) polypropylene, (b) polyvinyl chloride, (c) polythene, and (d) polymethyl methacrylate. The task is to determine which of these polymers is used for optical lenses.

Step 2: Identify properties of optical lens material

Consider the properties required for a polymer to be used in optical lenses. These include clarity, transparency, and optical quality. Hence, the polymer should have excellent light transmission properties.

Step 3: Analyze each option

- **Polypropylene**: Not commonly used for optical applications due to its lower clarity. - **Polyvinyl Chloride (PVC)**: Mainly used in construction and pipes, not known for optical clarity. - **Polythene (Polyethylene)**: Used in packaging and containers, lacks the transparency needed for lenses. - **Polymethyl Methacrylate (PMMA)**: Known as Plexiglass, it is a clear plastic with excellent light transmission, suitable for optical lenses.

Step 4: Draw conclusion

Based on the analysis, polymethyl methacrylate (option d) matches the required properties for optical lenses due to its clarity and excellent optical qualities.

Key Concepts

Polymers

Polymers are large, chain-like molecules made up of small repeating units known as monomers. They form the basis of countless materials used in everyday life. Polymers have diverse properties and can be tailored for specific applications based on their chemical structure.

This flexibility is what makes polymers so versatile in industry and manufacturing. For example, their properties can be altered to be more flexible, durable, or transparent, depending on their intended use.

• Some common types of polymers include plastics, rubbers, and fibers.
• These materials account for a wide range of products from bottles to clothing to industrial components.

Understanding the basic characteristics of polymers helps in choosing the right type for a specific application, such as optical lenses, which require excellent optical clarity and transmission of light.

Material Properties

Material properties refer to the characteristics that define how a material behaves under various conditions. These properties are crucial in determining the material's use in specific applications.

For optical lenses, certain material properties are incredibly important. The lens material must allow light to pass through without scattering or absorbing it significantly.

• **Transparency**: The ability of a material to transmit light without significant scattering.
• **Refractive Index**: This determines how much a material can bend light, which is critical for focusing and forming clear images.
• **Durability**: The resistance of a material to damage or scratching is essential for maintaining clarity over time.

By understanding these properties, engineers and manufacturers can select the right materials for producing high-quality optical lenses.

Polymethyl Methacrylate (PMMA)

Polymethyl Methacrylate, or PMMA, is a clear, thermoplastic polymer known by various trade names like Plexiglass or Acrylic. It is widely used in applications where transparency and durability are needed.

PMMA is ideal for optical lenses because of its outstanding optical properties:

• **Excellent Clarity**: PMMA allows up to 92% of light to pass through, which is higher than many other polymers.
• **Scratch Resistance**: Compared to other transparent plastics, PMMA is relatively harder and more scratch-resistant.
• **Lightweight**: It offers a great advantage over glass by being much lighter, making it easier to handle and install.

These properties make PMMA an excellent choice for not only prescription lenses but also a range of other optical applications, from camera lenses to screens.