Our Biology is to Blame for Virtual Images... Not Physics - Parth G Explains Optics

This is why Virtual Images need to be studied! It's as much biology as it is physics.

Hi everyone, I'm back with another video on a topic that I used to find tricky when I first studied it. We're discussing how real and virtual images are formed, as well as what the difference is between them, and why virtual images even exist.

I decided to go about looking at this topic by considering the light passing through a convex lens. We see three "rules" that an ideal (thin) convex lens must obey:
1) Any light passing through the lens' focal point and then through the lens will be refracted so it moves parallel to the optical axis on the other side.
2) Any light entering the lens while moving parallel to the optical axis will be refracted so it moves through the focal point on the other side.
3) Any light passing through the absolute centre of the lens will not change direction.

These three rules are simplifications that don't quite apply to real lenses, but they are very good approximations and make our understanding much clearer too. Incidentally, we can apply similar logic when studying concave lenses, as well as convex and concave mirrors. But each of these has their own set of rules as dictated by their geometry.

We see how an object placed further than the focal point of a convex lens will have its light refracted such that an inverted real image is formed on the other side of the lens. We also see that this image is formed by the actual convergence (meeting) of light rays coming from the lens. Therefore, if an observer were to place their eye where the rays of light focus, they would see an image of the object. Additionally, if we were to place a screen at that same point, an inverted image would be projected on that screen.

If we now consider an object placed closer to the convex lens than its focal point, then the rays of light passing through the lens are refracted in such a way that they will never meet on the other side. The light rays are said to "diverge", and not "converge". So it seems they will not form an image.

However, our brains are very interesting organs. When converging rays of light enter our eyes, our brain will interpret them as if emerging from a point source. In other words, our brain will "trace" the rays of light back to a supposed source. This means that what we end up seeing is an image of the object, that is often bigger than the object, and seemingly further back too. This is known as a virtual image.

It's important to note that a virtual image cannot be projected on a screen because it's not formed by the convergence of light rays. It's more a projection created by our own brains.

In other words, the reason we study virtual images and not just real images, is because biology is very interesting and our brain imagines light rays as if moving through air, rather than through the lens which changes the path along which they travel!

Thumbnail Image Credit: Paul Skorupskas

Timestamps:
0:39 - The Properties of Convex Lenses
2:40 - How Physicists Study Image Formation in Optics
3:29 - Real Images: Converging Light Rays
6:07 - Virtual Images: Diverging Light Rays
7:19 - Why We Study Virtual Images At All (Hint: Ask the Biologists!)

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Видео Our Biology is to Blame for Virtual Images... Not Physics - Parth G Explains Optics канала Parth G