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: 3×10 8 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: Incident ray Normal Reflected ray Angle of incidence Angle of reflection Mirror

Using mirrors Two examples: 1) A periscope 2) A car headlight

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 بدلا من المرآتين و لكن فكرة العمل واحدة. ففى الحالتين يكون السطحان العاكسان متقابلين و متوازيين و يكون وضعهما بحيث ينحرف مسار الضوء الساقط على السطح زاوية مقدارها 90 درجة

Refraction

Camera consists of lenses of glass or convex and depends in its work on the refraction of light

AIR Critical angle (2) When we increase the angle of incidence (i), the angle of refraction (r) increases until AIR glass AIR glass AIR glass i r normal

AIR glass Critical angle (3) when the angle of refraction is 90 o, the incident angle is called the critical angle (C). AIR glass r 90 o normal i C

Total internal reflection When the incident angle is larger than the critical angle, total internal reflection will occur (at the interface). water AIR 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.optical phenomenon

السراب الصحراوي كيف يحدث السراب الصحراوي؟ عندما تكون الشمس ساطعة ترتفع درجة حرارة سطح الارض فتسخن طبقة الهواء التي فوقها فتكون درجة حرارة الهواء في الطبقة التي تليها أقل سخونة وهكذا تنتقل الاشعة الصادرة عن الاجسام على سطح الارض من منطقة هواء بارد نسبيا الى أخرى أسخن فتنكسر الاشعة 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 الاشعة الضوئية تنكسر عند سطح مبتعدة عن العمود المقام وامتداد هذه الاشعة المنكسرة يشكل خيال السمكة بالنسبة للمشاهد على سطح الارض. 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