The image of an external object formed on the retina of the human eye by the eye lens is

Introduction / Context:
The human eye functions as a natural optical instrument, using a convex lens system to form images of external objects on the retina. Understanding the nature of this image is a standard concept in basic optics and biology. This question asks whether the image on the retina is real or virtual and whether it is upright or inverted.

Given Data / Assumptions:

• The eye contains a convex lens system consisting of the cornea and the crystalline lens.
• The retina is a light sensitive screen at the back of the eye.
• Objects are located at normal viewing distances greater than the focal length of the eye lens system.
• We consider normal healthy vision without defects.

Concept / Approach:
A convex lens produces a real, inverted image of an object when the object is placed beyond the focal length of the lens. The human eye adjusts its focal length through accommodation to bring light from different distances to focus exactly on the retina. The retina receives this focused light pattern just like a screen, so the image must be real and inverted. Although we perceive objects as upright, this is due to processing by the brain, which interprets and corrects the visual information, not because the retinal image itself is upright.

Step-by-Step Solution:
Step 1: Model the eye as a convex lens (the eye lens) forming an image on a screen (the retina). Step 2: Recall that for a convex lens, when the object distance is greater than the focal length, it forms a real image on the opposite side of the lens. Step 3: Such a real image is inverted with respect to the object. Step 4: In the human eye, the retina is physically located where this real image forms, so the retinal image must be real and inverted. Step 5: Therefore the correct description of the image on the retina is that it is real and inverted, even though our perception after brain processing is upright.

Verification / Alternative check:
In laboratory experiments, if you dissect a large animal eye and place a bright object in front of it, you can sometimes see an inverted miniature image on the retina when light passes through the lens system. This demonstrates directly that the retinal image is real and inverted. Eye diagrams in textbooks also show inverted images on the retina along with explanations of how the brain interprets them as upright. These experimental and textbook observations confirm the real and inverted nature of the retinal image.

Why Other Options Are Wrong:
Virtual and upright would require the retina to be on the same side of the lens as the object or the lens to behave like a simple magnifier, which is not how normal vision works for distant objects.
Virtual and inverted is not a standard image type for a single convex lens and does not match the eye structure.
Real and upright would require an unusual lens arrangement or object location not typical of the human eye in normal use.
Magnified and virtual for all objects describes a simple magnifying glass used very close to the eye, not the natural imaging situation in the eye for everyday distances.

Common Pitfalls:
Students sometimes confuse the retinal image with perception. Because we always see objects upright, they conclude that the image on the retina must also be upright. Another confusion arises from using magnifying glasses, which do form a virtual, upright image, but that is a separate optical setup. To avoid mistakes, keep in mind the lens formula and remember that the retina plays the role of a screen, so the eye forms a real, inverted image which the brain later interprets as upright.

Final Answer:
The image of an object formed on the retina of the human eye is real and inverted.