Register to reply

Optics, far point, near point

by sixpence
Tags: optics, point
Share this thread:
sixpence
#1
Jul28-08, 12:43 AM
P: 1
I'm having trouble deciding what to use as the object, p, and the image, q. For example heres a question:

An individual is nearsighted; his near point is 13cm and far point is 50cm. What lens power is needed to correct his nearsightedness? When lenses are in use, what is this person's near point?

so i got 1/infinity + 1/-.5 = 1.f

1/-.5 = 1/-.13 +1/q

these are the right answers but they don't make sense to me. How would the focal length from the far point have anything to do with wearing glasses. I also don't know when to make things negative or keep it positive, but that's mainly b/c I don't know whats the image and whats the object. I don't know if the questions are just worded poorly but I can't seem to get them. Is the near point always the object or can it be object and image? This is frustrating meeeeeee
Phys.Org News Partner Physics news on Phys.org
Step lightly: All-optical transistor triggered by single photon promises advances in quantum applications
The unifying framework of symmetry reveals properties of a broad range of physical systems
What time is it in the universe?
G01
#2
Jul28-08, 08:23 PM
HW Helper
G01's Avatar
P: 2,685
The near point is the closest something can be so that the person can still see it clearly. The far point is the farthest away something can be so that the person can still see it.

Since the person can't see any farther away than the far point, we want to make glasses from lens that will take objects which are really far away (object distance =infinity) and put the image at the far point.

So, the object distance in this problem is infinity. The image point will be the near point. Does this clear things up?


Register to reply

Related Discussions
Why triple point of water is higher than freezing point Classical Physics 7
Is every point of every closed set E subset of R^2 a limit point of E? Calculus & Beyond Homework 2
Shortest time from a point to a moving point Calculus 5
Calculating point X on the Golden Spiral knowing a point and a distance Calculus 0
Distance from a point on a sphere to a point on a plane... Calculus 6