Unit 5. light
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  • La luz es un tipo de radiación que se propaga en ondas. Las ondas que pueden propagarse en el vacío se llaman ondas electromagnéticas. La luz es la radiación electromagnética.La luz visible es la luz que le permite ver el color y las formas de los objetos. La luz puede provenir de una fuente natural o una fuente artificial.
  • La luz viaja en línea recta. Se viaja en ondas y no requiere de un medio.La velocidad de la luz sin embargo, no depende del medio.La velocidad de la luz en el vacío y en el aire es bastante similar, alrededor de 300.000 Km / s.Se toma a la luz tan sólo ocho minutos en viajar desde el Sol a la Tierra.
  • Se refleja cuando llega a una superficie reflectante.Cambia de dirección al pasar de un medio a otro (se refracta).
  • Algo que demuestra la propagación lineal de la luz es la formación de sombras.Un opaco objeto colocado delante de una fuente de luz va a crear una sombra.Una sombra es la zona oscura donde hay poca o ninguna luz.La sombra tendrá la misma forma que el objeto de su creación, esto se debe a que la luz viaja en línea recta.
  • La refracción de la luz es el cambio de rumbo experimentado por los rayos de luz que pasa de un medio a otro en el que se propagan con diferente velocidad. Por ejemplo, al pasar del aire al agua, la luz se refracta
  • Las leyes fundamentales de la refracción son :El rayo refractado, el incidente y la normal se encuentran en el mismo plano.El rayo refractado se acerca a la normal, ya que pasa de un medio en el que se propaga más rápido que otro que se propaga más lentamente. Por otro lado se aleja de la normal cuando se pasa a un medio que se propaga con mayor rapidez.
  • La luz blanca es una mezcla de colores: si un haz de luz blanca pasa a través de un medio dispersante, por ejemplo, un prisma, los colores se separan debido a que tienen diferentes índices de refracción.
  • Una lente es un dispositivo óptico con simetría axial perfecta o aproximada que transmite y refracta la luz, convergentes o divergentes de la viga .Se utilizan para fines muy diferentes: gafas, lupas, binoculares, lentes de cámaras, telescopios, etcUna lente simple consiste en un solo elemento óptico. Una lente compuesta es un conjunto de lentes simples (elementos) con un eje común;Las lentes suelen ser de vidrio o plástico transparente.
  • Lentes convergentes: Son más gruesas en el centro que en los bordes. Los rayos refractados por ellas convergen en un punto llamado la atención.Lentes divergentes: Son más gruesas en los bordes que el centro. Rayos refractados no convergen en un punto, pero por separado.
  • Trasmisión DE OBJETOS A TRAVÉS DE LA LUZLos objetos pueden ser transparente, translúcido u opaco. Esto depende de cómo la luz viaja a través de ellos:OBJETOS TRANSPARENTES  que permiten que la luz viaje a través de ellos. Aire, agua, vidrio. objetos translúcidos que absorben un poco de luz y permiten a algunos a viajar a través. Cebolla de papel y vidrio esmerilado. objetos opacos que absorben la mayor parte de la luz que reciben. Ellos no permiten que la luz viajan a través de. Un pedazo de papel oscuro, un trozo de madera, un pedazo de metal.
  • Rojo, azul y verde son los colores primarios de la luz. La mezcla de estos colores se pueden producir todos los colores del espectro.Los colores secundarios de la luz son amarillo, magenta y cian.Mediante la mezcla de: rojo + verde amarilloRojo + azul magenta Verde + azul cian 
  • Cuando la luz blanca pasa a través de un cristal de color, sólo una parte de esta luz blanca se transmite. Depende del color del objeto. Si vemos un objeto a través de un cristal de color, el color que vemos el objeto depende de su color original y el color del cristal también.
  • Un "emétrope" ojo es el que es capaz de centrarse en los objetos lejanos y cercanos. Pero hay algunos defectos asociados con la visión: Miopía: Un problema con la capacidad de enfoque del ojo. Es cuando el ojo no es capaz de enfocar correctamente los objetos en la distancia. Esto ocurre cuando la córnea se convierte en una forma diferente (demasiado curvada) de lo normal o cuando el ojo es más largo de lo normal por lo que hace que la luz entra en el ojo para enfocar en un punto dentro del ojo antes de la retina. Esto hace que el ojo y el cerebro para ver la imagen del objeto distante como una imagen borrosa. Lente divergente nos ha de corregir la condición.
  • Hipermetropía: El globo ocular es más corto de lo normal y la imagen de los objetos cercanos se forma detrás de la retina. Las personas con esta condición tienen problemas para enfocar objetos cercanos. Se puede corregir con lentes convergentes.Astigmatismo: un defecto muy común es debido a deformidades en la curvatura de la córnea. La visión no es clara.

Unit 5. light Unit 5. light Presentation Transcript

  • UNIT 5. LIGHT Presentation by Liannette Bellido Cintrón Natural Sciences 2˚ ESO I.E.S. FRANCISCO RODRÍGUEZ MARÍN FEBRARY 2011
  • WHAT IS LIGHT?
    • Light is a type of radiation that spreads in waves. The waves that can spread in a vacuum are called electromagnetic waves. Light is electromagnetic radiation.
    • Visible light is the light which allows you to see the colour and shapes of objects. Light can come from a natural source or an artificial source.
  • Electromagnetic waves are classified according to frequency as shown in the diagram below: Light is the radiation of the electromagnetic spectrum that we can capture with our eyes.
  • SPEED OF LIGHT
    • Light travels in a straight line. It travels in waves and does not require a medium.
    • The speed of light however, does depend on the medium.
    • The speed of light in a vacuum and in the air is quite similar, about 300,000 Km/s.
    • It takes light just eight minutes to travel from the Sun to the Earth.
    Nothing in nature can go faster than the speed of light.
  • Properties of light
    • The light has three distinctive properties:
    • Propagates in a straight line.
    • It reflects when it reaches a reflecting surface.
    • Changes direction as it passes from one medium to another (is refracted).
  • SHADOWS
    • Something which proves the linear propagation of light is the formation of shadows.
    • An opaque object placed in front of a source of light will create a shadow.
    • A shadow is the dark area where there is little or no light.
    • The shadow will have the same shape as the object creating it, this is because light travels in straight lines.
    • If a source of light, big or small, is very far from an object it produces sharp shadows .
    • The less sharp area around the shadow is called shade or penumbra
    Shadow Shadows and Penumbras
  • SOLAR ECLIPSE
    • A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is fully or partially covered. This can only happen during a new Moon, when the Sun and Moon are aligned to the Earth. At least two and up to five solar eclipses can occur each year on Earth, with between zero and two of them being total eclipses.
  • TYPES OF SOLAR ECLIPSES fa There are four types of solar eclipses:
    • A total eclipse occurs when the Sun is completely obscured by the Moon. The intensely bright disk of the Sun is replaced by the dark silhouette of the Moon.
    • An annular eclipse occurs when the Sun and Moon are exactly in line, but the apparent size of the Moon is smaller than the Sun’s size. Hence the Sun appears as a very bright ring, or annulus, surrounding the outline of the Moon.
    • A hybrid eclipse (also called annular/total eclipse ) transitions between a total and annular eclipse. At some points on the surface of the Earth it is visible as a total eclipse, whereas at others it is annular. Hybrid eclipses are comparatively rare.
    • A partial eclipse occurs when the Sun and Moon are not exactly in line and the Moon only partially obscures the Sun.
  • LUNAR ECLIPSE
    • A lunar eclipse occurs when the moon passes behind the Earth such that the Earth blocks the sun’s rays from striking the moon.
    • This can occur only when the Sun, Earth and Moon are aligned exactly, or very closely so, with the Earth in the middle.
    • That means there is always a full moon the night of a lunar eclipse.
  • SOLAR ECLIPSE vs LUNAR ECLIPSE
    • Unlike a solar eclipse, which can only be viewed from a certain relatively small area of the world, a lunar eclipse may be viewed from anywhere on the night side of the Earth.
    • A lunar eclipse lasts for a few hours. A total solar eclipse lasts for only a few minutes at any given place.
    • The reflection of light is represented by two rays: the one that arrives at the surface , the incident ray , and the one that “bounces” from the reflective surface, the reflected ray .
    • If you draw a line perpendicular to the surface (this line is called called normal), the incident ray makes an angle with that line, which is called the angle of incidence .
    Reflection normal
  • The laws of reflection are as follows : 1.The incident ray, the reflected ray and the normal are in the same plane perpendicular to the reflective surface. 2.The angle of incidence is equal to the angle of reflection. Normal
  • Why do we see objects? We can see objects around us because light the reflected in them reaches our eyes. There are two types of light reflection:
  • Light Refraction The refraction of light is the change of direction experienced by light rays passing from one medium to another in which they propagate with different speed. For example, when passing from air to water, the light is refracted.
    • The fundamental laws of refraction are:
    • The refracted ray, the incident and the normal are in the same plane.
    • The refracted ray gets closer to the normal as it passes from a medium in which it spreads faster to another that it spreads slower. On the other hand it moves away from the normal when it passes to a medium that it spreads faster.
  • The dispersion of light, a demonstration of refraction
    • White light is a mixture of colors: if a beam of white light passes through a dispersant medium, for example, a prism, the colors are separated because they have different refractive indices.
  • LENSES
    • A LENS is an optical device with perfect or approximate axial symmetry which transmits and refracts light, converging or diverging the beam.
    • Are used for very different purposes: glasses, magnifying glasses, binoculars, camera lenses, telescopes, etc
    • A simple lens consists of a single optical element. A compound lens is an array of simple lenses (elements) with a common axis;
    • Lenses are typically made of glass or transparent plastic.
  • Types of simple lenses
    • Converging Lenses: They are thicker in the middle than at the edges. The rays refracted by them converge at a point called the focus.
    • Diverging lenses: They are thicker at the edges than the center. Refracted rays do not converge at a point, but separate.
    • TRASMISION OF LIGHT TROUGH OBJECTS
    • Objects can be transparent, translucent or opaque. This depends on how light travels through them:
    • TRANSPARENT OBJECTS  they allow light to travel through them. Air, water, glass.
    • TRANSLUCENT OBJECTS  they absorb some light and they allow some to travel through. Onionskin paper and frosted glass.
    • OPAQUE OBJECTS  they absorb most of the light they receive. They don’t allow light to travel through. A dark piece of paper, a piece of wood, a piece of metal.
  • PRIMARY COLOURS OF LIGHT Red, blue, and green are the primary colors of light. Mixing these colors can produce all of the colors of the spectrum. The secondary colours of light are yellow, magenta and cyan. By mixing: Red + green  yellow Red+ Blue  magenta Green + Blue  cyan  
  • TRANSMISSION OF COLOUR BY TRANSPARENT AND COLOURED OBJECTS
    • When white light passes through a coloured crystal, only a part of this white light is transmitted. It depends on the object’s colour.
    If we see an object through a coloured crystal, the colour we see the object depends on its original colour and on the crystal’s colour too.
  • An “emmetropic” eye is one that is able to focus on both far and near objects. But there are some defects associated with the vision: Defects of vision Myopia : A problem with the focusing ability of the eye. It is when the eye is not able to focus properly on objects in the distance. It happens when the cornea becomes a different shape (too curved) from normal or when the eye is longer than normal and so causes light entering the eye to focus on a point within the eye before the retina. This causes the eye and brain to see the image of the distant object as a blurred image. Diverging lens are used to correct the condition.
  • Hypermetropia: The eyeball is shorter than normal and the image of nearby objects is formed behind the retina. People with the condition have problems focusing nearby objects. It can be corrected using converging lenses. Astigmatism: a very common defect is due to deformities in the curvature of the cornea. The vision is not clear.