GS-2 Physical Sciences Question 2

[anuradharo8690]

I was wondering if you could clarify this question with an example based on the lens maker equation similar to what you did for question 3. Thanks.

[admin]

Of course, you would never have to work this out since it should be known by the rules of lenses. Nonetheless, it can be confirmed as follows:

Let the first image distance = di = the object distance for the eyepiece

Let the focal point of the eyepiece = Fe

Let the image distance for the eyepiece = i

Because i is enlarged: i > di (absolute values)

Because i is virtual: i must be -ve

The lens equation:

1/o + 1/i = 1/f

thus

1/di - 1/xdi = 1/Fe

(x-1)/xdi = 1/Fe

Fe = xdi/(x-1)

So, if for example, x = 2, then Fe = 2di thus di < Fe.

[terryheidt1382]

This is still confusing me. Why would the image distance for the objective be equal to the object distance for the eyepiece? Wouldn't the object distance for the eye piece equal the distance between the lenses minus the image distance for the objective lens?

[jellywing_2058]

The answer lies in understanding the wording of the question. The question asks