Optics – How to Form an Image of a Virtual Object by Reflection

geometric-opticsopticsvisible-light

I was reading geometric optics when I came across the concept of virtual objects. I found the concept counter-intuitive, as far as reflection goes. (I perfectly understand the formation of such an object when the light ray is refracted through a glass slab.)

Attaching the definition provided in my book:

Virtual Object defn

My confusion: A mirror forms an image when the rays originate from a certain object. So, how can an image of a virtual object form if the rays do not diverge from a particular point in the first place? What are some real-life examples of such a situation, as depicted by the figure below:

fig

I have checked answers to similar questions but my doubt is not cleared.

Best Answer

So, how can an image of a virtual object form if the rays do not diverge from a particular point in the first place?

The image in your question shows a "virtual object". It does not show an image. You could create a real image from it, and in this case it would do exactly that in front of the mirror, if you finished drawing the rays.

This is just a definition, which is somewhat counterintuative, and it completes the set of real and virtual objects and images, the other three of which are somewhat more intuative.

  • Light diverges from a real object
  • Light appears to diverge from a virtual image (when an optic reflects or refracts it)
  • Light converges on a real image
  • Light appears to converge on a virtual object (except an optic gets on the way and refracts or reflects the light)

For real life examples its somewhat harder to come up with simple examples as a virtual object isnt often much use on its own. So it might be formed as an intermediary in a larger optical system. Or even in this example. If you have an imaging system with a fold mirror at the end, that mirror would create a virtual object, similar to your picture here.

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