0
$\begingroup$

We have a certain system of lenses:

Lens 1: Focal length: 19.5 cm Lens 2: Focal length : 9.5 cm

I put an object 36 cm away from lens 1. Then, I put lens 2 between lens 1 and a screen. The separation from lens 1 and 2 is 10 cm.

I want to know where the image will be formed.

I get the right numerical answer. However, I cannot seem to understand why we get a "negative m" (ie. a virtual image).

When I draw the ray diagram by hand, I get that the image is real.

Can someone explain to me what is going wrong?

$\endgroup$
  • $\begingroup$ Oh boy! I see my mistake. Virtual images have a POSITIVE magnification. Someone please confirm that this is true for all virtual images! $\endgroup$ – yolo123 Nov 23 '14 at 22:53
1
$\begingroup$

Your m is negative because the image is inverted, not because it's virtual. Inverted images have a negative magnification. Virtual images are caused when the rays diverge from a point. A lens with a negative focal length typically causes them. A convex lens also forms a virtual image when the object distance is shorter than the focal length of the lens.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.