Question 122 of 949
To produce an enlarged and erect image with a concave mirror,the object must be positioned
- A. at the principal focus
- B. beyond the centre of curvature
- C. between the principal focus and the centre of the curvature
- D. between the principal focus and the pole
Correct Answer:
D
Explanation
To determine the correct position of an object for a concave mirror to produce an enlarged and erect image, let's analyze the options provided and understand the principles of concave mirrors.
### Correct Option: D. Between the principal focus and the pole
#### Explanation of Why Option D is Correct:
1. **Understanding Concave Mirrors**: A concave mirror is a spherical mirror that curves inward. It has several important points:
- **Pole (P)**: The midpoint of the mirror's surface.
- **Principal Focus (F)**: The point where parallel rays of light converge after reflecting off the mirror. It is located between the pole and the center of curvature.
- **Center of Curvature (C)**: The center of the sphere from which the mirror is a part. It is located behind the mirror.
2. **Image Formation**: The nature of the image (enlarged, reduced, erect, or inverted) depends on the position of the object relative to these key points:
- **Object between F and P**: When the object is placed between the principal focus (F) and the pole (P), the rays diverge after reflecting off the mirror. However, they appear to come from a point behind the mirror, creating an erect and enlarged image. This is because the reflected rays diverge, and the brain interprets them as coming from a larger virtual image behind the mirror.
3. **Ray Diagrams**: If we were to draw a ray diagram:
- A ray parallel to the principal axis reflects through the focus.
- A ray passing through the focus reflects parallel to the principal axis.
- The intersection of these rays (or their extensions) gives the position of the image, which is virtual, erect, and enlarged.
#### Why the Other Options are Incorrect:
- **Option A: At the principal focus (F)**:
- If the object is placed at the principal focus, the rays of light will reflect parallel to the principal axis and will not converge or diverge to form an image. Instead, they will create an image at infinity, which is not visible. Thus, this option does not produce an image at all.
- **Option B: Beyond the center of curvature (C)**:
- When the object is placed beyond the center of curvature, the image formed is real, inverted, and reduced in size. The rays converge in front of the mirror, leading to a smaller image. Therefore, this option does not meet the requirement for an enlarged and erect image.
- **Option C: Between the principal focus and the center of curvature (F and C)**:
- In this case, the image formed is real, inverted, and enlarged. While it is enlarged, it is not erect. Thus, this option does not satisfy the condition of producing an erect image.
### Summary of Key Points:
- **Concave mirrors** can produce different types of images based on the object's position.
- **For an enlarged and erect image**, the object must be placed **between the principal focus and the pole**.
- **Ray diagrams** help visualize how light behaves when reflecting off concave mirrors.
- **Common pitfalls** include confusing the positions of the object and misinterpreting the nature of the image formed.
### Revision Summary:
- The correct position for an enlarged and erect image with a concave mirror is between the principal focus and the pole.
- An object at the principal focus does not produce a visible image.
- An object beyond the center of curvature produces a real, inverted, and reduced image.
- Understanding ray diagrams is crucial for visualizing image formation in concave mirrors.