Which of the following form virtual and erect image for all positions of a self- luminous subject

Options

A. Convex lens
B. Concave lens
C. Convex mirror
D. Concave mirror

Answer

To solve the question of which optical instruments form a virtual and erect image for all positions of a self-luminous object, we will analyze the behavior of different types of lenses and mirrors.

### Step-by-Step Solution:

1. **Understanding Self-Luminous Objects**:
- A self-luminous object emits its own light, such as a bulb or a flame. The light rays from such objects can travel in all directions.

2. **Analyzing Convex Lens**:
- A convex lens can form both real and virtual images depending on the position of the object.
- When the object is beyond the focal point, a real image is formed. Only when the object is within the focal length does it produce a virtual image.
- **Conclusion**: A convex lens does not form a virtual and erect image for all positions of the object.

3. **Analyzing Concave Mirror**:
- A concave mirror can also form both real and virtual images.
- A real image is formed when the object is placed beyond the center of curvature. A virtual image is formed only when the object is placed between the focal point and the mirror.
- **Conclusion**: A concave mirror does not form a virtual and erect image for all positions of the object.

4. **Analyzing Convex Mirror**:
- A convex mirror always forms a virtual image regardless of the position of the object.
- The light rays diverge after reflecting off the convex mirror, and the virtual image appears behind the mirror.
- **Conclusion**: A convex mirror forms a virtual and erect image for all positions of the object.

5. **Analyzing Concave Lens**:
- A concave lens always diverges light rays, causing them to appear to come from a point behind the lens.
- Therefore, it always produces a virtual and erect image for any position of the object.
- **Conclusion**: A concave lens forms a virtual and erect image for all positions of the object.

### Final Conclusion:
The optical instruments that form a virtual and erect image for all positions of a self-luminous object are:
- **Convex Mirror**
- **Concave Lens**