# Calculating Power of Tear Layer in Contact Lens Prescription

• AngelLegs
In summary, the conversation discusses the power of a tear layer between the cornea and a contact lens for a mildly farsighted person with a near point of 29.0 cm. The problem involves finding the power of the combined lens, given the individual powers of the contact lens and the tear layer. The conversation also touches on the basic principles of combining powers of lenses.
AngelLegs

## Homework Statement

The contact lens prescribed for a mildly farsighted person is 1.25 D, and the person has a near point of 29.0 cm. What is the power in D of the tear layer between the cornea and the lens if the correction is ideal, taking the tear layer into account? Assume that a normal human has a near point of 25.0 cm.

## Homework Equations

P = 1/do + 1/di = 1/f

The tear+contact must make a compound lens with the power needed to correct eyesight with the stated near-point.
How do the powers of lenses combine?

Simon Bridge said:
The tear+contact must make a compound lens with the power needed to correct eyesight with the stated near-point.
How do the powers of lenses combine?
The two lenses would bee a double convex (in the eye) and the contact would be a convex, right?
But I'm confused about how to set up the problem.
One would be negative and one would be positive, right?

Go back to basics:
When you are given the nearpoint, and you want to know what power of lense will correct that eyesight - how do you work that out?
When you have two lenses one after the other with P1 and P1 ... how do you find the overall power P of the combined lens?

Note: the shape of the lens is irrelevant.

## What is the formula for calculating the power of a lens?

The formula for calculating the power of a lens is P = 1/f, where P is the power in diopters and f is the focal length in meters.

## What is the difference between positive and negative power lenses?

A positive power lens is a convex lens that converges light rays, while a negative power lens is a concave lens that diverges light rays. Positive power lenses are used to correct farsightedness, while negative power lenses are used to correct nearsightedness.

## How do you calculate the power of a compound lens system?

To calculate the power of a compound lens system, you can simply add the individual powers of each lens in the system. For example, if two lenses with powers of +4 diopters and -2 diopters are placed together, the resulting power of the system would be +2 diopters.

## What is the unit of measurement for lens power?

The unit of measurement for lens power is diopters (D). This unit is used to measure the refractive power of a lens, which is the ability of the lens to bend light.

## How does the power of a lens affect its ability to bend light?

The higher the power of a lens, the greater its ability to bend light. A lens with a higher power will have a shorter focal length, meaning it can bring light rays to a focus at a closer distance. A lens with a lower power will have a longer focal length, meaning it can bring light rays to a focus at a farther distance.

• Introductory Physics Homework Help
Replies
2
Views
3K
• Introductory Physics Homework Help
Replies
1
Views
4K
• Introductory Physics Homework Help
Replies
3
Views
3K
• Introductory Physics Homework Help
Replies
4
Views
2K
• Introductory Physics Homework Help
Replies
3
Views
2K
• Introductory Physics Homework Help
Replies
5
Views
818
• Introductory Physics Homework Help
Replies
1
Views
4K
• Introductory Physics Homework Help
Replies
8
Views
5K
• Introductory Physics Homework Help
Replies
3
Views
2K
• Introductory Physics Homework Help
Replies
3
Views
2K