When the object is at focus of a concave mirror, the image is formed at

Options

A. focus
B. centre of curvature
C. within focus
D. infinity

Answer

To determine where the image is formed when the object is at the focus of a concave mirror, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Setup**:
- We have a concave mirror with a focus (F) and a center of curvature (C).
- The object is placed at the focus (F) of the concave mirror.

2. **Draw the Ray Diagram**:
- Draw the principal axis of the mirror.
- Mark the focus (F) and the center of curvature (C).
- Place the object at the focus (F).

3. **Trace the Rays**:
- **Ray 1**: A ray parallel to the principal axis will reflect through the focus after striking the mirror.
- **Ray 2**: A ray passing through the center of curvature (C) will reflect back along its original path.

4. **Analyze the Reflected Rays**:
- The ray that was parallel to the principal axis reflects and passes through the focus (F).
- The ray that passes through the center of curvature retraces its path.

5. **Determine the Image Location**:
- Since the two reflected rays do not converge at any point, they appear to diverge from a point that is very far away.
- Thus, the image is formed at infinity.

6. **Conclusion**:
- Therefore, when the object is at the focus of a concave mirror, the image is formed at infinity.

### Final Answer:
When the object is at the focus of a concave mirror, the image is formed at infinity.

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