A thick plane mirror shows a number of images of the filament of an electric bulb. Of these, the brightest image is the

Options

A. First
B. Second
C. Last
D. Fourth

Explanation

To determine which image of the filament of an electric bulb appears the brightest when viewed in a thick plane mirror, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Setup**:
- We have a thick plane mirror and an electric bulb with a filament. The light from the filament will reflect off the mirror, creating multiple images.

2. **Light Reflection**:
- When light rays from the filament hit the mirror, some of the light is reflected back towards the viewer, while some may pass through the mirror (if it is thick enough) and reflect off the back surface.

3. **Formation of Images**:
- The first image (I1) is formed by the light that is directly reflected from the front surface of the mirror.
- The second image (I2) is formed by the light that passes through the mirror, reflects off the back surface, and then comes back to the front surface.
- Additional images (I3, I4, etc.) may be formed by further reflections, but they will generally have lower intensity due to multiple reflections.

4. **Brightness and Intensity**:
- The brightness of an image is directly proportional to the intensity of light reaching the observer.
- The intensity of light from the first image (I1) will be less than that of the second image (I2) because I2 is formed by a pure reflection from the back surface of the mirror, which typically reflects more light than the partial reflections.

5. **Comparison of Intensities**:
- Let’s denote the intensities of the images as follows:
- I1 (intensity of the first image)
- I2 (intensity of the second image)
- I3 (intensity of the third image)
- Since I2 is formed by pure reflection, it will have a greater intensity than I1 and I3. Thus, we can conclude that:
- I2 > I1 and I2 > I3

6. **Conclusion**:
- Therefore, the brightest image of the filament in the thick plane mirror is the second image (I2), formed by the pure reflection from the back surface of the mirror.

### Final Answer:
The brightest image is the second image formed by pure reflection (I2).