This document provides an overview of light and optics. It discusses different types of light sources, including primary sources like the sun and secondary sources like reflected light. It also covers transparent, translucent, and opaque materials, and how light propagates in straight lines. Experiments are suggested to explore these concepts, such as classifying objects as light sources or observing light reflection. The document aims to teach basic optics and light behavior.

1. THE CONDUCT OF THE LIGHT UNIT 1
Optics is the session in Physics where we estudy light.
1.-Light sources
-Primary light sources: Some objects emit light that is produced by themselves. Some
examples are: the Sun, a candle, a bulb and a television.
Types:
-hot: the source heats up the burb’s filament because of the heat generated by
electricity. This is an incandescence source.
-cold: the source gives light when an unload of electrons provoke fluorescent
substances that cover the surface of the TV screen.
-Secondary light sources: Things that are illuminated. They reflect part of the light that
arrives. For example: the planets Earth and Mars and the Moon.
ACTIVITIES:
1.- What kind of primary light source are: the Sun, a fluorescent tube, a candle, a glow-
worm, the numbers of a watch?
2.- Search in a dictionary the meaning of: incandescence, fluorescence,
phosphorescence and bioluminiscence.
3.- Some animals, for example the glow-worm, are be able to produce light. That
phenomenon is known as bioluminiscence. It is caused by a chemical reactions in the
animal’s cells.
-Do you know any bioluminescent animal? What use has that property?
-Is it hot or cold the source of light produced bioluminescent animals?

2. 4.- Classify the following, which are a primary light source which are a secondary light
source:
Jupiter, lava of a volcano, a piece of cast iron, the lines of the road, a bonfire, a
lighthouse and fireworks.
5.- When you observe the night sky you can see satellites. How can you see them if they
are not incandescent objects?
6.- What kind of light sources can used by pedestrians and the cyclists to be visible on
the road at night?
2.- Transparent, translucent and opaque materials.
There are objects that absorb most of the light. These allow us to see through
them and we know them as secondary sources.
When the light passes through the object, one part of the light is reflected and
the other part is absorbed by it. The absorption depends on the nature and thickness of
the object.
There are three types of object:
-A transparent object: this allows light to pass through the object, so much so
that you can clearly see through it.
Example: window’s glass, pure water.
-A translucent object: this allows light to pass through slightly. You can
distinguish the objects partially. It’s semi-transparent
Example: dirty window’s glass, water dissolved salts.
-An opaque object: this does not allow light to pass through. They’re
impenetrable by sight.
Example: desk, blackboard.
ACTIVITIES:
7.- Classify which are transparent, translucent and opaque from the following objects
and materials: wood, glass, tracing paper, air, water, a cloud, the human body and a
metal plate.
8.- The only enviroment totally transparent is the vacuum. All the rest of the
environments are made up matter. They absorb light partially or totally.
-If the water is transparent, explain why is it when you dive deeper why does the
brightness of the water decrease?

3. EXPERIMENT:
Why do you see through a sheet of paper when you put it on the window’s
glass? Repeat the experiment with four or five sheets of paper. Explain what happens.
3.-Straight propagation of the light.
When light hits an opaque object it generates a shade where the light can’t arrive.
The formation of the shadow shows that:
In a transparent enviroment the light is propagated in straight line.
EXPERIMENT:
Draw and cut an object out. Shine the light at it with a torch and see its shadow on
the wall of the class. Make a drawing of the shade seen and indicate the dark and half-lit
area.
Light emission:
-Light ray: the straight line of the light from the source.
-Beam: a joint of light rays emitted from the source.
There are different kinds of rays in a beam:
- A ray: it is projected on the screen.
- B ray: it passes softly through the figure and then hits the screen.
- C ray: it can’t pass through the object so it doesn’t hit the screen.
EXPERIMENT:
Look at the drawing.
What do you see projected on the screen if you shine the two lights at the same time?

4. ACTIVITIES:
9.- When you make up animal’s shadows at the wall with your hands, where do you
have to move your hands to the shadow bigger? Towards the light or the wall? Why?
10.- Observe the picture and draw the shadow of the tree on the land.
11.- What do the crew of a spaceship see at the space?
12.- Where do you have to use the sunshade to protect the eyes of a baby?

5. 4.-Shining phenomenons.
- Refraction: The turning or bending of any wave, such as a light or sound wave,
when it passes from one medium into another or different optical density.
- Refrexion: The act of reflecting, or turning or sending back, or the state of being
refrected.
The smooth surface forms clear images.
The rough surface doesn’t form clear images.
- Chromatic dispersion: The white light ray passes through prism and breaks
down into a coloured beam (the colours spectrum).

6. ACTIVITIES:
13.- Why does the calm water act like a mirror but the waves of the water doesn’t?
14.- Draw the reflexion on a smooth surface and on a rough surface.
15.- Search at the dictionary the meaning of “dispersion” and “chromatic”
.
16.- What colours does the white light spectrum have?
The rainbow is formed when the light is break down in the water drops of the
humid air.
EXPERIMENT:
Observe the spectrum of the white light at:
-The surface of a CD when the light shines on the grooves of the surface, look at the
breakdown of the white light.

7. - Diffraction net or a transparent sheet.
COMPLEMENTARY ACTIVITY
Read The laser (Annex 2)
REVIEW
Answer of: What have you learnt?(Annex 3)

8. THE COLOR OF THE LIGHT AND OF THE OBJECTS
UNIT 2
1.-Analysis of the light.
At night, all the objects are black and we don’t distinguish them. When the light
arrives at the objects, the color appears. The color of the object changes depending on
the kind of light that goes to an object.
We can observe the continous espectrum of the white light with a spectroscope.
The light is composed by the seven colors of the rainbow in the Sun’s light or in a burb.
It’s then, when you can see two shinning bands in the blue and green part of the
spectrum in the Ultraviolet light of the fluorescent.
EXPERIMENT:
Work in pairs. Observe two kinds of light (burb and fluorescent) with a
spectroscope.
We can have coloured light using filters.
A filter is a transparent or coloured filter made of glass or plastic.
EXPERIMENT:
Work in small groups and observe trough diferent coloured filters and look the
colour changes of the objects.
Put a coloured filter in front of the white light focus. The filter absorbs totally or
parcially the rest of the colours, and it only let the colour of the filter in that we are
observing.
If the filter let only one kind of color in, the reflected light is monochromatic.
2.-Addition of colour.
EXPERIMENT:
Project the light emited for three focus on a white screen.
The lights have to be red, blue and green light. Observe the reflected colours on
the screen. We can obtein the white light with the synthesis of superposition of the three
primary colours.
You obtain the secundary colours by superposing the two primary colours.
red + blue magenta
green + blue cyan
red + green yellow
The combination of colours is known as additive synthesis.
Observe and discuss the secundary colours, as a result of the primary colours light
(red, green and blue).

9. 1.-green 4.-cyan
2.-blue 5.-yellow
3.-red 6.-magenta
APPLICATION:
The addition of the colour light is used in the TV receptors.
EXPERIMENT:
Observe the TV screen with magnifying glass.
You can see a colour dots (red, blue and green). The colour pixels are actived when
the electrons come out of the TV tube, crash and provoke fluorescent substances, that
cover the internal part of the TV screen.
The diferent combination of the three colours give all the coloured spectrum. If
the three primary colours are provoked at the same level, you can see the white colour
and if they don’t, you can see the black colour.
ACTIVITIES:
1.-Classify the seven colours of the white light spectrum in primary and
secundary colours.
2.- Which is the TV screen colour when the following colours are activated?
- red and blue:
- blue and green:
- red and green:
3.-Why it you look through a magnifying glass the TV screen on, you can see
dots of three colours (red, blue and green), while the images are of diferents colours?

10. 2.-The colour of the objects.
There are a cells named cones at the eye’s retina. These cells react in diferent
way depending on the wave lenght ot he incident beam that arrives.
The perception of the colour is because the lightly waves arrive at our eyes. The
waves became nervous impulse and they are sended at the brain. There they are
interpreted.
There are people who have dificulties to distinguish some colours because of a
retina’s defect or an anomaly at he nervous process of sight. This anomaly is named
daltonism. The name comes from the british chemist John Dalton, who was daltonic and
he was the first scientist who imvestigated the illness.
Another illness connected with the colour perception is the acromatopsy and the
people who suffer it only watch in black and white colours.
EXPERIMENT:
Observe directly colored objects, including white and black colours, by
superposing filters of diferent colours with white light .
-White object: This object reflects all the light and don’t absorb any tipe of
light. Iluminated: -directly with white light: you watch white colour at the object.
Reflects all the colours and don’t absorbes anything.
-with white light or coloured filters: the object have the colour of
the light project at the object.
-Coloured object: The object reflects the light of its colour and it absorbs the
rest of lights.
Iluminated: -with white light or filter of its colour: you observe the object
with the same colour.
-with light or filter of another colour: the colour of the object
changes.
-Black object: The object don’t reflect any colour because it absorbes all the
colours.
Iluminated with white light, though you put a coloured filter: it shows always
its colour. It can’t reflect any kind of light.
CONCLUSIONS:
An object reflects the light of its colour and it absorbs the light of all the colours.
The quantity of the reflected light depends of the incident light and the nature of
the surface of the object.
ACTIVITIES:
4.- Copy the sentence with the correct option:
- A white object iluminated with red light, looks: white/red/black.
- A red object iluminated with red light, looks: red/white/grey.
- A red object iluminated with green light, looks: green/grey/red.
5.-Explain why you can’t play chess in a room iluminated with blue light.

11. EXPERIMENT:
Observe a green apple through a red filter. Do an scheme of the beam light and
indicate the colour of it.
Explain what you observe.
6.- Draw two circles (one green and one red) at your notebook. Observe them with two
filters (one green and one red). Take notes of the colour you can see at the circle:
4.-Obtain the colour.
Antique human used to dye clothes of diferent coloured inks and draw cave
paintings and pictures.
Inks contains pigments, chemist substances that no reflect any colour but reflect
a wide part of the spectrum of the white light.
The base colours of the pigments are magenta, cyan and yellow. They are known
as a primary colours.
(I explain my exprience work at the quality control laboratories at the chemist industry
of pigments and inks for graphics arts)
Mixture of pigments
Making mixtures with the primary colours, we can obtain the rest of the colours.
If you mixt the colours in diferent proportions you can obtain diferents tones of the
same colour.
The only colour you can’t obtain mixturing pigments, is the white colour.
Mixturing equal parts of primary pigments, you can obtain the secundary
colours:
-cyan + yellow green
-magenta + yellow orange
-magenta + cyan violet
EXPERIMENT:
Complete the squeme of the crhomatic circle with the primary colours and the
secundary colours. (The students only will have watercolours fo the primary colours for
doing the experiment activity).

12. REVIEW:
Answer of: What have you learn? (Annex 4)
COMPLEMENTARY ACTIVITY: (Annex 5)
Read: “The season colours”
EXTRA ACTIVITY:
The students will choose an item (related with the colour) and they will develope it in a
composition. The teacher will correct it and then they will be able to read it at the next
session class.
At the activity, the teacher evaluate the development of the item, the grammar
and the coherence of the composition.
Items:
1- A city of colours.
2- The nature and theirs colours.
3- The people’s colour.
4- The animal’s colour.
5- Colours and sensations.
6.- The rainbow.
7- The language of the colours.
8- The name of the colours.
9- The colour of the signals.
10- The colours at the design.
11- Natural substances with colours.
12- The pigments.
13- The addvertisments and the colour.
The students should read the text: “The colour of the autumm” as an exemple. It
can help them to write their composition. (Annex 6)

13. THE LIGHT REFLEXION UNIT 3
1.-The reflexion
The light reflects when arrives at a surface, it bonces and return changing the
direction..
The reflexion law: it is formed by 2 principle:
-The incident ray and the reflexion ray are at the same plane.
-The incident angle and the reflection angle are the same.
Are all the reflexion the same?
-The smooth surfaces, like the mirrors, reflect the light in a specular image. After
the reflexion at the mirror, the parallel rays continue parallel and form clear images.
-The rough surfaces, as paper, reflect light in a difuse image. After the reflexion at
the surface, the parallel rays reflect at different directions and the rays don’t form clear
images.
2.-The difuse reflexion and the illumination
The major part of the objects reflect the light desorderly, because of their rough
surface. These objects have a difuse reflexion. If the surface is rougher, the reflexion is
more difuse.
The difuse reflexion of the light is the base of lightling.
In all the reflexion, we lose intensity. The reflected ray never is so intens as the
incident ray (the materials absorb light radiation).
The bright materials are better reflectors than the matt materials. The mirrors are
the best reflectors because they only lose the 10% of the intensity.

14. The white color reflect light better than the rest of the colors and it gives more
brightness.
EXPERIMENT:
Cut two equal piece of aluminum foil. Turn off the light of the class. You put the
two aluminum foil over the desk, one smooth paper and the other rough paper. You
light them with a torch.
What kind of reflexion do you observe? What difference there are between the two
illumination?
ACTIVITIES:
1.- If the focus that illuminate the desk look at the ceiling. Does the light arrive at the
desk?
2.- Why a room painted in blue is less light that a room painted in white?
3.- What color would you paint the botton of the stage (of a theatre) if you don’t want to
see behind the staff during the play? Why?

15. 3.-The especular reflexion and the mirrors.
The mirrors are opaque, smooth and shiny bodies that reflect the light regulary.
They are made of a smooth sheet of glass and one of the faces are coved of silver.
The sheet of silver is protected with varnish.
It’s possible to product less fragile mirrors, if you silver a transparent sheet of
plastic.
plain
Tipes of mirrors concave
curved
convex
-Plain mirrors: They show a real image of the object with the same size of the real
images.
However, the right part of the image is the left part of the object, an viceversa.
Examples: dressing room, bathroom.
-Convex mirrors: They allow to see through them in a less size a big area.
Examples: rear-view mirror, exit park car.
-Concave mirror: They give a big image of a small area.

16. Examples: dressing table mirror (to shave, to pluck ...).
ACTIVITIES:
4.- The draw represents a beam of light. It arrives parallel at the concave mirror.
Draw the way of the reflected rays.
5.- Why the glass pieces of the broken bottle can provoke a fire?
6.- The draw shows the light rays of a burb, placed in the focus of a concave mirror.
Draw the way of the rays when they are projected to the mirror.

17. APPLICATION:
The mirrors are used in the construction of the optical instruments: telescopes,
periscopes, kalidoscopes and cameres.
4.-The images at the mirrors.
Image: reproduction of an object for optical instruments.
Reals: you can project images on the screen.
Example: projection of a film or a transparency.
Types
Virtuals: you can’t projectimages on a screen.
-Images from a plain mirror: The image formed from a plain mirror, seem find
behind the mirror at the same distance that the object. It’s a virtual image, you can see it
but you can’t project it on a screen.
-Images from a a convex mirror: The mirror gives virtual and smaller images than
the object that represents.
As in case of the opposite side of a spoon. The image forms is smaller than the
object.
-Images from the concave mirror: They are virtual and bigger than the object.

18. Also, the concave mirror forms a real, inverse and bigger image. The size of the
image become smaller if you move the object away of the mirror.
As in case of a spoon. It forms a inverse and small image.
EXPERIMENT:
Put a candle in front of a plain mirror. Cut na piece for doing a screen and try to
project the image of the candle on the screen.
Is the image virtual?
Measure the height and width of a box. Put the box in front of a plain mirror and
measure the height and width of the image.
What relation there are between the height of the object and the image?

19. Each student write his name with capital letters in a sheet of paper. Can you read the
name at the mirror? Copy the image of the mirror in another paper and put it in front of
the mirror. Can you read it now?
ACTIVITIES:
7.- Explain the characteristics of the plain mirror images.
8.- How do you demostrate than the convex mirror give virtual images?.
9.- What variation you obsere at the image when you move the object nearer to a
convex mirror? Could be the image bigger than the objectt?
10.- Are the images of the mirror always straight (no inverse)?
REVIEW: Answer of : What have you learnt? (Annex 6)

20. EXPERIMENT: Construction of an optical instrument:
The kaleidoscope.
The kaleidoscope was a popular toy at XIX century. It was invented by David
Brewsted at 1817. He was a Scottish physic who was interested in optics.
In these instrument the light bounce and generate images of images.
The students will build their kalidoscope:
-The kalidoscope is formed by three rectandular, plain mirrors joint for the large
side and formed an angle of 60º.
-The joint mirrors are put inside of a roll of 13 cm (the same large of the mirrors).
-Put a top of card with a hole in the middel to see inside the kalidoscope.
-The other top is made of transparent material. It has to allow pass the light in and
you can see the little coloured papers inside.
-If you round the kalidoscope, the papers move and because of the reflection, you
can see different forms.
-When the instrument is finished. The students can paint it outside with
watercolors.

21. THE LIGHT REFRACTION UNIT 4
1.- The speed of light.
Light travels faster than sound. In thunder, you see the flash of lightning and then
followed by the sound. When you set a firework off, you see the light first and then that
is followed by the sound of the explosion.
The value of light speed in a vacuum is:
v = 300.000 Km/s = c
It is a very important piece of information in Physics.
Light can propagate in other mediums.
Example:
-when you look in the air, you can see the Sun’s light that arrives on Earth.
-through the transparent objects.
The speed of light in different mediums:
Mediums Speed (Km/s)
Water 225.000
Air 300.000
Alcohol 220.600
Benzene 200.000
Diamond 124.000
Ice 227.000
Glass 14.300-15.800
ACTIVITIES:
1.- Bear in mind the previous list of light speed in different mediums:
-What you can say about the light speed in the air?
-Is the light speed in any medium, bigger or smaller than in the vacuum?

22. 2.- If light from a star takes three seconds to hit Earth. What is the distance between the
star and Earth?
3.- In astronomy, they use the length unit in light years. It is the distance that light
covers in a year.
How many kilometres is it?
Refraction index:
It is represented by n and it indicates the relation between the vacuum speed (c)
and the speed in the medium ( v ).
n = VACUUM SPEED (C)
MEDIUM SPEED (V)
ACTIVITIES:
4.- Complete the list:
Medium Speed (Km/s) n
Water 225.000
Air 300.000
Alcohol 220.600
Benzene 200.000
Diamond 124.000
Ice 227.000
Glass 214.300-153.800
5.- Is the refraction index in a medium is bigger or smaller than the unit?

23. 6.- If light travels faster in water than in alcohol. If the light speed is big, then the
refraction index is also big. So is the refraction index bigger in alcohol or in water?
2.-The refraction causes a change of speed.
Refraction: A light ray through the surface between two mediums can cause a
change at the speed angle.
EXPERIMENT: Look of a coin in a glass of water.
The rays turn aside because of the reflexion. It seems that the coin is bigger and
nearer to the surface.
Refraction is making this look like an optical illusion.

24. The angles of the incident ray and refracted ray are now not the same.
Refraction is not possible if the incident ray is perpendicular with the separation
surface of the two mediums.
-If light propagates slower at the second medium then the reflected ray goes nearer
to the perpendicular.
The speed of light gets smaller the nearer the ray is to the perpendicular.
-If light propagates quicker in the second medium, the reflected ray is futher away
from the perpendicular.
ACTIVITIES:
7.- The picture represents the light refraction between two mediums.
What medium are the water and the glass?.

25. 8.- Complete the direction of the light ray shown in the following pictures:
9.- What picture represents the refraction of a ray through wide glass?
Write an example that represents the other picture.

26. The refraction of the light also depends on the colour. Red light refracts less than
blue light.
When white light passes through a prism, it forms a spectrum of light. The blue
colour appears in one extreme (more turned aside) and the red colour in the other
extreme (less turned aside).
3.-The limited angle and total reflexion.
Limit angle
- Only if the incident angle becomes bigger.
- Also if the refraction ray becomes bigger.
- In this case, the refracted ray is at the separation
surface between the two mediums.
When the incident angle is the limit angle,
the refraction angle is 90º.
Total reflexion
If the incident ray is bigger than the limit angle,
there is not refraction. The separation surface of the
two mediums work as a mirror and all the light is reflected.
It is the total reflexion.
The reflected ray is shinier because there is no reflaction.
APPLICATION:
There are a lot of instruments where there is total reflexion.
For example: Optical fibres, binoculars, periscopes and microscopes.
4.-The study of lenses.
Lenses are made of glass or transparent plastic.
There are lenses in magnifying glasses, wearing glasses and cameras.
There are two types of lenses:
Divergent:
- Are wider at the extremes.
- Show smaller images.
- Work as a convex mirror.
- Form straight images.

27. Light rays pass through a divergent lens:
Light rays pass through a divergent lens:
Convergent:
- Are wider at the middle.
- Show bigger images.
- At short distance away it acts like a concave mirror.
- Form straight images.
Light rays pass through a convergent lens:
Potència d'una lent: (Sessió 5)
La potència d'una lent és la inversa de al distància focal:
The power of the lens
Power = 1 / f units: f: meter
Power: dioptre.
If the total distance is smaller, the lens power is bigger.

28. EXPERIMENT:
-See if your glasses (or your classmate glasses) have a convergent or a divergent
lens.
-Check if the magnifying glass is a convergent lens.
ACTIVITY:
10.- What is the power of the lens if its total distance is 5 dm?
-Simplify the power of 4 dioptres. What is the total distance seen using these
glasses?
REVIEW:
Answer of: What have you learnt? (Annex 7)
COMPLEMENTARY ACTIVITY:
Read: The mirages (Annex 8)

29. THE EYE. STRUCTURE AND FUNTIONS UNIT 5
1.-External structure of the eye.
The eyeball and another structures such as the eyelids, the eyelashes, the tear duct
and the ocular muscles from the principles of vision.
Eyelids: the upper and lower fold of skin that close and cover the eye.
Eyelashes: hair growing on the edges of the eyelid.
Tear duct: products tears, a salted and transparent liquid that dampen the eye.
Oculars muscles: these allow the movement of the eye. Both eyes act
synchronically.
2.-Internal structure of the eye.
Internally, the eye is an aspheric globe of opal walls with the following
components:
Pupil: the expanding and contracting opening in the iris of the eye, through which
light passes to the retina.
Optic nerve: this consists of sensory fibres that conduct impulses from the retina
to the brain.
Cornea: the transparent anterior part of the external coat of the eye, it protects the
iris and the pupil.
Iris: the circular diaphragm forming the coloured portion of the eye and containing
a circular opening, the pupil, in its centre.
Aqueous humor: the watery fluid that fills the space between the cornea and the
crystalline lens in the eye.
Crystalline lens: a doubly convex, transparent body in the eye, situated behind the
iris, which focuses incident light on the retina. The contractions of the ocular muscles

30. change the thick of the crystalline lens for seeing the objects clearly at different
distances.
Vitreous humor: transparent gelatinous substance filling the eyeball behind the
crystalline lens.
Retina: the innermost coat of the posterior part of the eyeball that receives the
image produced by the lens, is continuous with the optic nerve, and consist of several
layers, one of which contains the rods and cones that are sensitive to light.
EXPERIMENT: Dissection of a calf eye
Material: a calf eye, a scalpel, a forceps, a dish and latex gloves.
Method:
-Observe the eye externally and identify the cornea, the iris, the pupil and the optic
nerve.
- Cut the eye with the scalpel. The substance that appears is the vitreous humor.
What is the colour of this substance?
-Empty the eye out. Find and clean the crystalline lens. What kind of lens it is?

31. -Look inside the eye. Look at the appearance ot the iris and the pupil. What is the
black layer in the eye?
EXPERIMENT: Prove the existence of the blind dot.
The internal parts of the eye are black, except a yellow region named the mascula.
The mascula is the part of the retina that is less sensitive to light. It is where the nerve
optic is conneted to the eyeball. Commonly, it is known as the blind dot.
Method:
-Look the drawing of the cross on the left and the circle on the right.
-Cover your right eye and look at the drawing. Look at the dot on the right hand
side with your left eye.
-Now repeat the experiment but now cover your left eye. Look at the cross on the
left with your right eye.
X O
Can you explain the lost of visibility that you experience?

32. 3- The eye as a dark chamber.
EXPERIMENT: The use of a dark chamber.
The teacher shows the use of a dark chamber to the students.
The eye works as a dark chamber. It is a dark and closed box. In one side there are
holes that have different diameters. The light comes inside the box through these holes.
The pupil works as the holes, it controls the pass of the light inside.
There is a translucent piece of paper at the opposite side of the holes. You can see
the inverse image of the object on the paper. The retina works as the translucent paper..
Sight is more complex than the dark chamber because it distinguishes the colour.
Measure the distance and value of the form and the movement of the objects.
The neurological system that transmits the information between from the retina to
the brain does it inversely. There, the image is interpreted back straight.
Both eyes don’t see the same. Each eye sends different images of objects to the
brain. The brain then processes these two images and it forms a three-dimensional
image. So, you perceive the image of the objects.
The dark chamber was an instrument discovered by the famous painter and
inventor Leonardo da Vinci. He discovered the dark chamber when in summer on the
wall of a dark room; he could see the inverse image of the outside landscape. This was
the first idea of the dark chamber. Centuries after, it became the photographic camera.

33. 4.-Vision’s anomalies.
The eye can have defects in its structure or functions. Some of these defects can
be corrected with different types of lenses:
-Presbyopia: Old people have a crystalline lens that is less elastic and it can’t modify its
form. These people have to step back from text to read it. This anomaly has to be
corrected with convergent lenses.
-Myopia or short-sightedless: Some people have shortened eyesight or the cornea and
crystalline lens are curved too much. In this case, the image is projected in front of the
retina. So, these people can’t see it formed correctly at larger distances. This anomaly is
corrected with divergent lenses, because they have to move closer to the image to
project it on the cornea.
-Hypermetropia or long-sightedness: The images are formed behind the retina because
people with this anomay have lengthened eyesight. Either that or the cornea or
crystalline lens isn’t curved enough. People with this anomaly can’t see correctly at
short distances. It can be corrected with convergent lenses.

34. REVIEW:
What have you learnt? (Annex 9)
COMPLEMENTARY ACTIVITY:
Read: The eclipse (Annex 10)
Observe, understand and comment: The optical illusions. (Annex 11)

35. Il·lusions òptiques