Transcript Slide 1 - hwazen

Unit 3
Optics and light
lesson 1:reflaction revision
Define visible light :It is a form of
energy that we can detected by our
eyes
Light speed is:3×108 m/s
law of reflection
• When light is reflected the incidence ray, the
reflected ray, and normal all lie in the same
plane
• Angle of reflection =angle of incidence
Read pg 126 in physics for
you
Reflection from a mirror:
Normal
Reflected ray
Incident ray
Angle of incidence
Mirror
Angle of
reflection
Using mirrors
Two examples:
2) A car headlight
1) A periscope
Application of reflection
any of a number of optical
instruments that enable the user to
view objects that are not in the direct
line of vision, such as one in a
submarine for looking above the
surface of the water. They have a
system of mirrors or prisms to reflect
the light and often contain focusing
lenses
‫البيريسكوب فى الغواصة يستخدم منشورين بدال من‬
‫ ففى الحالتين يكون‬. ‫المرآتين و لكن فكرة العمل واحدة‬
‫السطحان العاكسان متقابلين و متوازيين و يكون وضعهما‬
‫بحيث ينحرف مسار الضوء الساقط على السطح زاوية‬
‫ درجة‬90 ‫مقدارها‬
Refraction
Camera consists of lenses of glass
or convex and depends in its work
on the refraction of light
Critical angle (2)
• When we increase the angle of incidence (i),
the angle of refraction (r) increases until ......
normal
glass
glass
i
r
AIR
AIR
o, the
• when the angle
of
refraction
is
90
Critical angle (3)
incident angle is called the critical angle
(C).
normal
glass
iC
90or
AIR
Total internal reflection
• When the incident angle is larger than the
critical angle, total internal reflection will
occur (at the interface).
AIR
water
Next
Application of total internal
reflection
mirage
rainbow
optical fibers
Pg:131
• A mirage is a naturally occurring optical
phenomenon in which light rays are bent to
produce a displaced image of distant objects
or the sky.
‫• السراب الصحراوي‬
‫كيف يحدث السراب الصحراوي؟‬
‫عندما تكون الشمس ساطعة ترتفع درجة حرارة سطح االرض فتسخن‬
‫طبقة الهواء التي فوقها فتكون درجة حرارة الهواء في الطبقة التي‬
‫تليها أقل سخونة وهكذا تنتقل االشعة الصادرة عن االجسام على سطح‬
‫االرض من منطقة هواء بارد نسبيا الى أخرى أسخن فتنكسر االشعة‬
‫عند السطح الفاصل بينهما مبتعدة عن العمود المقام على السطح‬
‫الفاصل من نقطة السقوط وتستمر كذلك الى أن تصل زاوية السقوط‬
‫الى زاوية أكبر من الزاوية الحرجة فتنعكس انعكاس كلي داخلى‬
‫ونتيجة لذلك يسير الضوء الى عين الناظر عبر المسار المبين في‬
‫الشكل المجاور على أنه خيال مقلوب‬
Optical fibres
Optical fibres
the angle at which the ray meets the normal at the surface is always much
more than the critical angle, so the ray continues down the fiber , with total
internal reflection.
at the other hand , we can see the light after many total internal reflection .
Optical fibers in communication
fiber-optic cables are now widely used in communication for carrying
telephone and tv signals.
if there are any scratches on the fiber, the light can escape, because a ray can
meet the surface of the scratch with an angle of incidence less than the
critical angle.
This is easily cured by coating the fiber with a tougher outside layer, made of
plastic or glass with a lower absolute refractive index.
• Why is the sky blue?
• A clear cloudless day-time sky is blue
because molecules in the air scatter blue
light from the sun more than they scatter
red light. When we look towards the sun
at sunset, we see red and orange colours
because the blue light has been scattered
out and away from the line of sight.
Sunsets
• When the air is clear the sunset will appear yellow,
because the light from the sun has passed a long
distance through air and some of the blue light has
been scattered away. If the air is polluted with small
particles, natural or otherwise, the sunset will be more
red. Sunsets over the sea may also be orange, due to
salt particles in the air, which are effective Tyndall
scatterers. The sky around the sun is seen reddened,
as well as the light coming directly from the sun. This
is because all light is scattered relatively well through
small angles--but blue light is then more likely to be
scattered twice or more over the greater distances,
leaving the yellow, red and orange colours.
Mirrors and lenses
• A mirror is a reflective surface. Light passes
through the glass and hits the silver backing,
reflecting off of it. (The angle of incidence
equals the angle of reflection.) A lens, on
the other hand, does not reflect light;
it refracts it. After entering the glass, light
refracts differently depending on the shape
of the lens and also creates a focal point
where the refracting light comes to a point.
This differs for different lenses -- convex or
concave -- which is why there are different
lenses for different types of eyeglasses.
Mirrors and lenses
How we can see
• light from the object will focus on your retinas
very precisely. When seeing an object close-up,
the focus is blurred very momentarily, but this is
unnoticeable, because your eye has an automatic
refocusing ability that makes the target clear. This
refocusing ability is called "Accommodation," and
it works by making the natural lens of the eye
larger or more convex in shape. As we get older,
we lose more and more of this ability, which is
why things close-up start to blur after about 45
years of age.
Our eyes
Sight Conditions
• SHORT-SIGHTEDNESS
Short-sighted, also known as near-sight or Myopia,
means that the light focuses in front of your retinas or
'too short.' This makes it difficult to see objects in the
distance whereas objects close-up are clearer. This
occurs when light from the objects seen focus in front
of the retina rather than on it. This is believed to
happen when the eyeball is slightly too long, and is
also known as Axial Myopia.
LONG-SIGHTEDNESS
Long-sighted, also known as far-sight or Hyperopia, means
the eyes focus "behind" or 'too long,' which makes it
difficult to see objects close up rather than from a distance.
This occurs when light from objects viewed will
theoretically focus behind the retina rather than on it.
However, because the eye is able to naturally fatten the
lens and cause light to bend more, this error in focus is
overcome. This explains why distance vision is usually good.
When the same individual tries to look at something up
close, much more effort is required, as light from a near
object will fall much further back behind the retina. Near
vision is therefore worse.
Apparent Depth Real Depth of water
We see the objects under water closer than their real depth to the
surface.
‫لماذا تبدو السمكة في حوض على عمق أقل من عمقها الحقيقي ؟ •‬
‫الجواب هو أن االشعة الضوئية تنكسر عند سطح مبتعدة عن العمود المقام وامتداد هذه‬
‫‪.‬االشعة المنكسرة يشكل خيال السمكة بالنسبة للمشاهد على سطح االرض‬
‫‪.‬يطلق على البعد الذي يبدو للمشاهد أن الجسم عنده (موضع الخيال )‪ :‬البعد الظاهري‬
‫عند انتقال الشعاع الضوئي من وسط خفيف (معامل انكسار مادته صغير) الى وسط‬
‫‪ .‬كثيف (معامل انكسار مادته كبير) يكون البعد الظاهري أكبر من البعد الحقيقي‬
‫عند انتقال الشعاع الضوئي من وسط كثيف(معامل انكسار مادته كبير) الى وسط خفيف‬
‫‪( .‬معامل انكسار مادته صغير) يكون البعد الظاهري أقل من البعد الحقيقي‬
‫عزيزاتي هذا كل ماهو‬
‫مطلوب من الوحدة الثالثة‬
‫الضوء للفصل الدراسي‬
‫الثاني‬