A circular planar wire loop is dipped in a soap solution and after taking it out, held with its plane vertical in air assuming thickness of film at the very small as sunlight falls on te soap film & observer receives reflected light.

Options

A. Th top portion appears dark while the first colour to be observed as one moves down is red.
B. The top portion appears violet while the first colour to be observed as one moves down in indigo
C. The top portion appears dark while the first colour to be observed as one move down in violet.
D. the top portion appears dark while the first to be observed as one move down depends on the refractive index of the soap solution.

Answer

To solve the problem regarding the circular planar wire loop dipped in a soap solution, we need to analyze the behavior of light as it interacts with the soap film. Here’s a step-by-step solution:

### Step 1: Understand the Setup
The circular wire loop is dipped in a soap solution and then held vertically in air. The soap film formed on the loop has varying thickness, being thicker at the top and thinner at the bottom.

**Hint:** Remember that the thickness of the soap film affects how light is reflected and refracted.

### Step 2: Light Interaction with the Soap Film
When sunlight falls on the soap film, it reflects and refracts. The colors we see depend on the thickness of the film and the wavelength of light. Thicker films tend to reflect different colors compared to thinner films.

**Hint:** Consider how different wavelengths of light (colors) interact with varying thicknesses of the film.

### Step 3: Color Absorption and Reflection
As the thickness of the soap film decreases from top to bottom, the colors of light will be absorbed in a specific order. The colors of visible light can be arranged from violet (shortest wavelength) to red (longest wavelength).

**Hint:** Recall the order of colors in the visible spectrum: Violet, Indigo, Blue, Green, Yellow, Orange, Red.

### Step 4: Determine the Appearance of the Top Portion
At the top of the loop, where the film is thick, the light will reflect in such a way that it appears dark because the thicker film absorbs certain wavelengths more effectively.

**Hint:** Think about how thicker films can lead to destructive interference for certain wavelengths.

### Step 5: Identify the First Color to be Absorbed
As you move down the loop, the first color that will be absorbed is red because it has the longest wavelength. As you continue moving down, the colors will change, and the first color that can be seen will be violet at the very bottom.

**Hint:** Remember that the order of absorption is influenced by the thickness of the film.

### Step 6: Conclusion
Based on the analysis, the top portion of the soap film appears dark, and the first color to be absorbed as one moves down is red. Therefore, the correct option is:

**Answer:** The top portion appears dark while the first color to be absorbed as one moves down is red.

### Final Answer
**Option A:** The top portion appears dark while the first color to be absorbed as one moves down is red.

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