Question

Rotation of planc-polarized light can be measured by (1) Manometer (2) Calorimeter (3) Polarimeter (4) Viscomcter

Short answer

Polarimeter

Step-by-step solution

Understand the Concept

When examining how plane-polarized light interacts with substances, specific instruments are used to measure changes, such as rotation of the light.

Identify the Options

The options given are: (1) Manometer, (2) Calorimeter, (3) Polarimeter, and (4) Viscometer.

Determine the Correct Instrument

A polarimeter is the instrument specifically designed to measure the angle of rotation caused by passing polarized light through an optically active substance.

Verify the Answer

The other options, Manometer (measures pressure), Calorimeter (measures heat changes), and Viscometer (measures viscosity), do not measure the rotation of plane-polarized light.

Key concepts

Rotation of plane-polarized light

When light waves oscillate in various planes, they are said to be unpolarized. However, when these waves are restricted to oscillate in a single plane, the light becomes plane-polarized. If this plane-polarized light passes through certain substances, its plane can rotate. This phenomenon is known as the rotation of plane-polarized light. The angle by which the plane rotates can give us valuable information about the properties of the substance it passed through. If the substance is optically active, it means it can rotate the plane of polarization. This rotation can be used to identify and measure various characteristics of the substance. The direction and magnitude of the rotation are commonly used to deduce the properties of materials in laboratories and various fields of science.

Optically active substances

Optically active substances have the unique ability to rotate plane-polarized light. This means that when light passes through these substances, the orientation of its oscillation plane changes. There are two types of optically active substances:

• Dextrorotatory: These substances rotate the plane of polarized light to the right, or clockwise.
• Levorotatory: These substances rotate the plane of polarized light to the left, or counterclockwise.

Some common optically active substances include sugars, amino acids, and certain crystals. The extent to which an optically active substance can rotate light is known as its specific rotation, and this property is inherent to the substance. By measuring the degree of rotation, scientists can identify the substance and understand its concentration in a solution.

Measurement instruments

Several instruments are used in scientific studies, each designed to measure specific properties. For measuring the rotation of plane-polarized light, the polarimeter stands out.

• Polarimeter: This instrument measures the angle of rotation caused by passing polarized light through an optically active substance. A polarimeter consists of a light source, a polarizer, a sample tube, and an analyzer.
• Manometer: Measures pressure, typically of gases or liquids. It is not used for optical measurements.
• Calorimeter: This device measures the amount of heat involved in chemical reactions or physical changes. It is unrelated to optical activity.
• Viscometer: Used to measure the viscosity, or resistance to flow, in fluids. It does not deal with light polarization.

The correct instrument to measure the rotation of plane-polarized light is the polarimeter. This device is crucial in chemistry and biochemistry for analyzing the concentration and properties of optically active substances.