In ray optics, an image formed by a plane mirror that cannot be received or captured on a physical screen is called what type of image?

Introduction / Context:
When light reflects from mirrors or passes through lenses, different kinds of images can be formed. These images are classified as real or virtual, and also as erect or inverted. Understanding the difference between real and virtual images is fundamental in ray optics. This question asks about the specific nature of the image formed by a plane mirror that cannot be projected onto a screen.

Given Data / Assumptions:

• The reflecting surface is a plane mirror.
• An image is seen in the mirror.
• The image cannot be obtained on a physical screen placed in front of the mirror.

Concept / Approach:
A real image is formed when light rays actually converge to a point, and such an image can be projected onto a screen. A virtual image is formed when light rays appear to diverge from a point behind the mirror or lens; the rays do not come from that point physically, so the image cannot be formed on a screen. Plane mirrors always form images that are virtual, erect, laterally inverted, and of the same size as the object. Therefore, the term that best matches an image that cannot be obtained on a screen is virtual image.

Step-by-Step Solution:
Step 1: Recall that a plane mirror produces images that appear to be behind the mirror. Step 2: Recognise that since the light rays do not actually meet behind the mirror, the image is virtual. Step 3: Note that virtual images cannot be formed on a screen because there is no real point of convergence of light rays. Step 4: Identify the option that describes an image not obtainable on a screen, which is a virtual image.

Verification / Alternative check:
You can test this by trying to place a sheet of paper in front of a plane mirror where you see your face. No matter how you position the paper, your face will not appear on the paper as a projected image. This shows that the image in the plane mirror is virtual. In contrast, with a converging lens and a suitably placed object, you can form a real image on a screen, demonstrating the difference.

Why Other Options Are Wrong:

• Real image: A real image can be projected onto a screen, so this does not match the behaviour of a plane mirror.
• Inverted image: The plane mirror forms erect, not inverted, images. Inversion refers to orientation, not whether the image can be captured on a screen.
• Erect image: While a plane mirror does form an erect image, erect does not indicate whether it is real or virtual. The key feature in the question is the inability to form the image on a screen, which defines virtual.

Common Pitfalls:
Students sometimes confuse erect with virtual and inverted with real, but these pairs are not always linked. For example, some virtual images can be inverted in certain optical systems. The correct distinction is whether light actually converges to form the image (real) or appears to originate from a point (virtual). Always focus on ray convergence and the possibility of projection onto a screen when deciding between real and virtual.

Final Answer:
An image formed by a plane mirror that cannot be obtained on a screen is a virtual image.