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# physics

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- CHAPTER 2 : Geometric Optics
  - Specific objectives
  - Introduction
  - Refraction
  - Reflection
  - Optical Instruments

Content:

## Optical Instruments

### the eye

- Eye modeling

The eye can be modeled as a converging lens (comprising the cornea and lens) with a variable focal length to accommodate the position of objects and form their images on the retina. The distance between this lens and the retina is called the depth of the eye. For a normal or emmetropic eye, the focal length is equal to the depth of the eye. The furthest point of distinct vision (the Punctum Remotum) is at infinity. The closest point of distinct vision (the Punctum Proximum) is at the minimum distance dm=25 cm from the lens.

The amplitude of accommodation is defined A by:

(PP)is the distance between the lens and the Punctum Proximum PP.

(PR )is the distance between the lens and the Punctum Remotum PR.

Eye Defects:

Among the eye defects, those resulting from refractive errors are corrected by appropriate lenses. Among these defects:

Myopia: a nearsighted eye is an eye that is too convergent, in this case OF ́<d ( F ́ is in front of the retina).

Hypermetropia: A hypermetropic eye is an eye that is not convergent enough OF>d ́( F ́ is behind the retina).

Presbyopia: is the loss of accommodation power with age.

Astigmatism: the focal length is not the same in all directions of observation.

### The magnifying glass

The magnifying glass is a converging lens that enlarges an object AB. For this purpose, AB it must be placed between the optical center O and the focal point F of the lens.

The algebraic distance OA of an image A'B'from an object AB is calculated using the conjugate relationship:

The magnification γ of the magnifying glass is calculated by the equation:

The power P of the magnifying glass is defined by the equation:

α' is the angle with which the observer sees the image A'B'. The unit of P is the diopter (𝜹).

The magnification of the magnifying glass is :

α The angle under which we observe the image is A'B'.

α'is the angle under which we observe the object AB from a distance dm where d_m represents the minimum distinct vision distance : dm=25cm=0,25m

Relation between G and P:

### Microscope

The optical microscope consists of two converging thin lenses.

- The objective with a focal distance O1F'1of a few millimeters produces a real, enlarged, and inverted image A1B1 of the object. The magnification of the objective AB is defined by

- The eyepiece (ocular) with a focal distance O2 F'2 of a few centimeters functions like a magnifying glass. It allows observing a virtual, enlarged image A'B'projected to infinity from A1B1. For this to happen, the image A1B1 of the object AB must be located in the object focal plane of the eyepiece. The point A1 must, therefore, coincide with the object focal F2 point of the eyepiece.

- The eyepiece power of an optical microscope is defined by the equation :

- The power of the microscope

- The magnification of the microscope

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