Lenses

[MedPR]

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Ok, so this has been something I've really struggled with (along with archimedes, which I still can't get), but hyperphysics just solved everything for me.

There is nothing to memorize about lenses except 3 things.

1. diverging lens = negative focal length
2. 1/o + 1/i = 1/f
3. M=-i/o

Everything else you can solve for pretty quickly from that.

 

[thais]

How about knowing what kind of images a concave lens will produce, a convex mirror... and etc. All that the EK book tells us to memorize?
Can we derive all that from your three points?

 

[MedPR]

How about knowing what kind of images a concave lens will produce, a convex mirror... and etc. All that the EK book tells us to memorize?
Can we derive all that from your three points?

Give me an example and we'll find out.

 

[mcloaf]

How about knowing what kind of images a concave lens will produce, a convex mirror... and etc. All that the EK book tells us to memorize?
Can we derive all that from your three points?

Once you work a few practice problems it's really not that many situations to memorize, and generally they're pretty intuitive.

 

[SaintJude]

Mmhh, really MedPr? Ok, I'll give you a problem...

For concave mirrors, where will the object need to be located to produce no image?

How would you solve that just knowing those 3 facts and not using ray diagraming. I'm not trying to be skeptical, just curious.

 

[milski]

Mmhh, really MedPr? Ok, I'll give you a problem...

For concave mirrors, where will the object need to be located to produce no image?

How would you solve that just knowing those 3 facts and not using ray diagraming. I'm not trying to be skeptical, just curious.

i=f or o=f leads to 1/o or 1/i being zero, which has not solution.

 

[SaintJude]

Milski! this was a challenge to medPr to demonstrate/explain how he uses only those 3 facts! Hmpf... 😉

Alright, medPr...another question.

Q. In a nearsighted individual, the image of a distant object is focused:

A. in front of the retina, requiring divergent lens correction
B. in front of the retina, requiring convergent lens correction
C. behind the retina, requiring divergent lens correction
D. behind the retina, requiring convergent lens correction

 

[milski]

Milski! this was a challenge to medPr to demonstrate/explain how he uses only those 3 facts! Hmpf... 😉

Alright, medPr...another question.

Q. In a nearsighted individual, the image of a distant object is focused:

A. in front of the retina, requiring divergent lens correction
B. in front of the retina, requiring convergent lens correction
C. behind the retina, requiring divergent lens correction
D. behind the retina, requiring convergent lens correction

I thought you were just curious. 😛

 

[MedPR]

Mmhh, really MedPr? Ok, I'll give you a problem...

For concave mirrors, where will the object need to be located to produce no image?

How would you solve that just knowing those 3 facts and not using ray diagraming. I'm not trying to be skeptical, just curious.

If no image is formed, then the image is formed at i=infinity.

i/f = 1/o + 1/i

So if you stick the object at the focal length, you get no image.

 

[MedPR]

Milski! this was a challenge to medPr to demonstrate/explain how he uses only those 3 facts! Hmpf... 😉

Alright, medPr...another question.

Q. In a nearsighted individual, the image of a distant object is focused:

A. in front of the retina, requiring divergent lens correction
B. in front of the retina, requiring convergent lens correction
C. behind the retina, requiring divergent lens correction
D. behind the retina, requiring convergent lens correction

I don't know what nearsighted means 🙁

Actually hang on let me think...

Nearsighted = can't see far away objects clearly? So the light hits your cornea and converges.. If you can't focus far away objects, you must be refracting light too much and having it converge at a place before your retina, so to prevent the over-refraction, you're going to want a diverging lens. So A.

Nothing to do with any of those equations though, so idk.

 

[SaintJude]

yeah! & that was a former mcat question 🙂

Edit: It looks like hyperphysics helped a lot. I also tried to memorize via EK approach. But I think I need to sit down tomorrow and just focus on light & optics.I understand how to ray diagram and all that other stuff, so if I give myself time I pray I'll full get the hang of it by end of tomorrow.

Nice going, medpr!

 

[MedPR]

yeah! & that was a former mcat question 🙂

Seems like a hard discrete, or a passage based question where they at least tell you what nearsightedness is 🙁

 

[MedPR]

yeah! & that was a former mcat question 🙂

Edit: It looks like hyperphysics helped a lot. I also tried to memorize via EK approach. But I think I need to sit down tomorrow and just focus on light & optics.I understand how to ray diagram and all that other stuff, so if I give myself time I pray I'll full get the hang of it by end of tomorrow.

Nice going, medpr!

With only 3 weeks left (less, actually) I decided to shortcut everything I don't know very well. Optics included. If I have time in the week before MCAT I'll relook at it and try to get it more.

Thinking more about your question has got me confused though. Where do you want the image to show up at? The focal length?

 

[milski]

For those of us who are nearsighted, eliminating two of the choices is extremely easy. I don't know if that's an unfair advantage or not. 😎