Young.s experiment is performed in air, water and glass. The descending order of fringe width for these media is

Options

A. water, air, glass
B. glass, water, air
C. air, water, glass
D. glass, air water

Answer

To solve the problem regarding the descending order of fringe width in Young's experiment performed in air, water, and glass, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Fringe Width**:
The fringe width (β) in Young's double-slit experiment is defined as the distance between two consecutive bright or dark fringes. The formula for fringe width in a medium is given by:
\[ \beta' = \frac{D \lambda}{d \mu} \]
where:
- \(D\) = distance between the slits and the screen,
- \(\lambda\) = wavelength of light,
- \(d\) = distance between the slits,
- \(\mu\) = refractive index of the medium.

2. **Identify the Refractive Indices**:
The refractive indices for the three media are:
- Air: \(\mu_{air} \approx 1\)
- Water: \(\mu_{water} \approx 1.33\)
- Glass: \(\mu_{glass} \approx 1.5\)

From this, we can see that:
\[ \mu_{glass} > \mu_{water} > \mu_{air} \]

3. **Determine the Relationship Between Fringe Width and Refractive Index**:
From the formula for fringe width, we can see that as the refractive index (\(\mu\)) increases, the fringe width (\(\beta'\)) decreases. This means:
- Higher \(\mu\) results in smaller fringe width.
- Lower \(\mu\) results in larger fringe width.

4. **Establish the Order of Fringe Width**:
Since we need the descending order of fringe width, we arrange them based on their refractive indices:
- Fringe width in air (\(\beta_{air}\)) > Fringe width in water (\(\beta_{water}\)) > Fringe width in glass (\(\beta_{glass}\))

Therefore, the descending order of fringe width is:
\[ \beta_{air} > \beta_{water} > \beta_{glass} \]

5. **Final Answer**:
The required descending order of fringe width for air, water, and glass is:
\[ \text{Air} > \text{Water} > \text{Glass} \]