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Home End HolisticTuition CashPlants Chapter 5: Light Form 4 1 Physics Next > The study of matter.

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Presentation on theme: "Home End HolisticTuition CashPlants Chapter 5: Light Form 4 1 Physics Next > The study of matter."— Presentation transcript:

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2 Home End HolisticTuition CashPlants Chapter 5: Light Form 4 1 Physics Next > The study of matter

3 Home End HolisticTuition CashPlants Objectives: (what you will learn) Objectives: (what you will learn) 1)understanding Light 2)understanding the Laws Physics: Chapter 5 2 < Back Next >

4 Home End HolisticTuition CashPlants Light Reflection 3 < Back Next > Light travels in straight lines. When light is incident on a surface, it is reflected. Laws of reflection of light a. The incident ray, the reflected ray and the normal are in the same plane. b. The angle of incidence is equal to the angle of reflection. Characteristics of images formed by plane mirror a. Same size as object b. Virtual c. Laterally inverted d. Upright. e. The image is as far behind the mirror as the object is in front

5 Home End HolisticTuition CashPlants 4 < Back Next >Refraction When light travels from one medium to another medium of different optical density, its speed changes. This causes the change in its direction and the light bends. The bending of light is called refraction. Laws of refraction a. The incident ray, the refracted ray and the normal lie on the same plane. b. The ratio of sine of angle of incidence to sine of angle of refraction is a constant (Snell’s Law). When light travels from an optically less dense to a denser medium, it bends towards the normal. When light travels from an optically denser to a less dense medium, it bends away from the normal.

6 Home End HolisticTuition CashPlants 5 < Back Next >Refraction Refractive index of medium X may be found by the following: n = Sine (angle of incidence) Sine (angle of refraction) n = Velocity of light in air Velocity of light in medium X n = Actual depth Apparent depth n = 1 Sine C, C = critical angle

7 Home End HolisticTuition CashPlants 6 < Back Next >Mirage Mirage A naturally-occurring optical phenomenon, in which light rays are bent to produce a displaced image of distant objects or the sky. The interpretation of the image is up to the fantasy of human mind, and is usually mistaken for a small puddle of water. The word comes to English via the French ‘mirage’, and from the Latin ‘mirare’, meaning 'to appear, to seem'. It has the same root as for mirror. Like a mirror, a mirage shows images of things which are elsewhere. The principal physical cause of a mirage, however, is refraction rather than reflection. It is also caused by the phenomenon of total internal reflection which is the result of refraction.

8 Home End HolisticTuition CashPlants 7 < Back Next >Mirage Inferior Mirage Cold air is denser than warm air, and has a greater refractive index. As light passes from colder air above to warmer air below it bends away from the normal, resulting in an inferior image for the sky above. Superior Mirage Where the air near the ground is cooler than that higher up, the light rays will curve downwards, producing a superior image. Superior mirages are most common in polar regions, especially over large sheets of ice with a uniform low temperature.

9 Home End HolisticTuition CashPlants 8 < Back Next > Internal Reflection Critical angle is angle of incidence when light travels from denser medium to less dense medium and angle of refraction is 90 o. C Normal Less dense medium Denser medium When light travels from denser to less dense medium and the critical angle is exceeded, total internal reflection takes place. Application of total internal reflection: optical fibres A light ray enters fibre at an angle > critical angle Total internal reflection takes place along whole length of the fibre.

10 Home End HolisticTuition CashPlants 9 < Back Next >Lens There are 2 types of lenses: convex and concave lenses Convex lens: the point where refracted rays meet is called focal point Concave lens: the light rays seem to be diverged from a single point, the point is the focal point Focal length ( f ): distance from optical centre to focal point Power of lens = 1 f (in metre), unit is dioptre (D) A real image can be formed on a screen. A virtual image cannot be formed on a screen. Optical instruments which use lenses: CameraPhotocopier Magnifying glassSlide projector MicroscopeTelescope

11 Home End HolisticTuition CashPlants 10 < Back Next >Lens u v f +=Lens equation: v u Magnification of lens = Object distance (u) Image distance (v) Characteristics of image Uses u < fSame side as object Virtual, upright, enlarged Magnifying glass u = fAt infinityVirtual, upright, enlarged Telescope f < u < 2fv > 2fReal, inverted, enlarged Slide projector u = 2fv = 2fReal, inverted, same size Photocopier u > 2fF < v < 2fReal, inverted, diminished camera

12 Home End HolisticTuition CashPlants 11 Summary < Back What you have learned: 1.Understanding Light 3.Using the Laws Thank You 2.Reflection and Refraction


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