UNIDAD: 12.- LUZ Y SONIDO ¿QUÉ ES LA LUZ? La luz es una forma de energía electromagnética. Partículas muy pequeñas llamadas fotones, se mueven en forma de ondas. La luz visible es la luz que nos permite ver los colores y la forma del los objetos. La luz puede venir de una fuente natural o artificial. Ejemplo: el Sol es una fuente natural, y las bombillas, las antorchas y velas son fuentes artificiales. Podemos ver un objeto si recibe luz. En este caso, absorbe parte de la luz, y refleja el resto en todas direcciones. Los objetos pueden ser:  Transparentes: No absorbe la luz y permite que la luz pase a través de él. Ejemplo: el cristal, el aire, etc.  Translúcidos: Absorbe parte de la luz y permite pasar algo de luz a través de él. Ejemplo: el papel cebolla, el cristal helado, etc.  Opacos: Absorbe la mayor parte de la luz que recibe y no permite a la luz pasar a través de él. Ejemplo: un papel oscuro, un trozo de madera, etc. PROPIEDADES DE LA LUZ:  Velocidad de la luz: La luz viaja en línea recta y por ondas. No necesita un medio. La velocidad depende del medio. En el vacío y en el aire es aproximadamente 300,000 km/seg.



Reflexión de la luz: Cuando un rayo de luz choca con una superficie, rebota y cambia de dirección. El rayo incidente choca en la superficie. El rayo reflejado rebota de la superficie. El ángulo de incidencia es igual que el ángulo de reflexión.

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Refracción de la luz: La luz se refracta cuando pasa de un medio a otro que tiene una diferente densidad. En esta situación, en vez de rebotar la luz se dobla en el límite entre los dos medios.

Las lentes son discos hechos de cristal o plástico con una o dos caras curvadas. Hay dos tipos: -

Lentes convergentes: Son más gruesas en el centro que en los bordes. Concentran los rayos de luz. Ejemplo: una lupa de cristal.

-

Lentes divergentes: Son más gruesas en los bordes que en el centro. Dispersan los rayos de luz. Ejemplo: las gafas de una persona corta de vista.

¿CÓMO PUEDEN LOS OJOS VER LOS COLORES? Las ondas de luz visible son las únicas ondas electromagnéticas visibles por el ojo humano. Los ojos pueden ver estas ondas como los colores del arco iris. Cada color tiene una longitud de onda diferente y tu retina puede distinguir estas diferentes longitudes de ondas. Luego tu cerebro interpreta esta información como colores. ¿QUÉ ES UN SONIDO? El sonido es una forma de energía mecánica que se produce por la vibración de un objeto. El sonido viaja por ondas a través de los sólidos, líquidos y gases. No puede viajar en el vacío. La velocidad del sonido depende del medio: es 340 m/s en el aire, 1,500 m/s en el agua y 5,130 m/s en el hierro. Las cualidades del sonido son:  Intensidad: Los sonidos pueden ser alto o suave, dependiendo de la amplitud del la onda Sonora. La intensidad del sonido se mide en decibelios (dB).  Tono: Los sonidos pueden ser altos o bajos dependiendo de la frecuencia de sus ondas. Esto diferencia las notas altas y bajas de la misma intensidad, producidas por un instrumento musical. El tono se mide en Hertzios (Hz).  Timbre: Nos permite identificar la fuente de sonido que tiene la misma frecuencia e intensidad. Diferentes instrumentos pueden identificarse por su timbre. ¿CÓMO SE REFLEJA EL SONIDO? El sonido se refleja cuando una onda sonora encuentra un obstáculo. La onda sonora rebota y cambia de dirección.  La reflección del sonido se usa en muy diferentes campos: - Ondas ultrasónicas se usan para explorar el interior el cuerpo humano. - El sonar usa la reflexión del sonido para detectar objetos en el mar o medir la profundidad del océano.  La reflexión del sonido produce dos fenómenos: - Eco: Es producido cuando un sonido se refleja en un obstáculo. El obstáculo debe estar situado al menos a 17 metros. Los dos, el sonido inicial y el sonido reflejado se escuchan. Las superficies duras reflejan el sonido mejor que las superficies blandas. - Reverberación: Ocurre cuando un sonido se refleja en un obstáculo que está a menos de 17 metros. El sonido inicial y el reflejado se escuchan, pero se mezclan. ¿QUÉ EL LA POLUCIÓN DE LUZ Y SONIDO? Una excesiva cantidad de luz y sonido puede tener efectos adversos.  Contaminación luminosa: Ocurre cuando las personas y los animales se exponen a una constante y fuerte luz. Las fuentes de luz artificial incluye las farolas de las calles, los anuncios luminosos, los focos de los campos de fútbol, etc. Algunos de los efectos adversos pueden ser: - La imposibilidad de ver el cielo de noche. - Los recursos y la energía se malgastan. - En la migración los pájaros colisionan con los edificios iluminados. - Los hábitos de las plantas cambian.  Contaminación sonora: La contaminación sonora o ruidosa ocurre cuando las personas o animales se exponen a niveles de sonidos que son estresantes o dañinos para el oído. El ruido es producido por el tráfico rodado, aeronaves, trenes, industria y centros de entretenimiento, como bares y discotecas. Cómo reducir la contaminación sonora: - Los edificios pueden estar aislados para no dejar pasar los sonidos fuertes. - El recorrido de vuelos de los aviones puede ser desviado lejos de las ciudades. - El tráfico se puede reducir en el centro de las ciudades. - La legislación puede establecer límites en la intensidad del ruido de los centros de entretenimiento.

NAME:_________________________________________ DATE:__________ 2º ESO___ (Bilingual)

UNIT: 12.- LIGHT AND SOUND WHAT IS LIGHT? Light is a form of electromagnetic energy. Very small particles called photons move in a wave pattern. Visible light is the light which allows you to see the colours and shapes of objects. Light can come from a natural or an artificial source. Example: the Sun is a natural source, and light bulbs, torches and candles are artificial sources. We can see an object if it receives light. In this case, it absorbs some of the light, and reflects the rest in all directions. Objects can be:  Transparent: They do not absorb light and allow light to pass through. Example: a glass, the air, etc.  Translucent: They absorb some light and allow some to pass through. Example: onion skin paper, frosted glass, etc.  Opaque: They absorb most of the light they receive and do not allow light to pass through. Example: a dark piece of paper, a piece of wood, etc. 1.- Copy this text:

2.- Translate these words: Light: Photon: Transparent: Translucent:

3.- What is visible light?:

4.- Why can we see objects?

Wave pattern: Opaque:

5.- What is a photon?

6.- What is a transparent body?

7.- What is a translucent body?

8.- What is an opaque body?

9.- Write ‘opaque’, ‘translucent’ or ‘transparent’ below each picture.

10.- a) Write down the name of ten opaque objects:

b) Write down the name of ten transparent objects:

NAME:_________________________________________ DATE:__________ 2º ESO___ (Bilingual) PROPERTIES OF LIGHT:  Speed of light: Light travels in a straight line and in waves. It does not require a medium. The speed depends on the medium. In a vacuum and in the air it is about 300,000 km/sec.



Reflection of light: When a ray of light hits the surface, it bounces off, and changes its direction. The incident ray hits the surface. The reflected ray bounces off the surface. The angle of incidence is equal to the angle of reflection.

1.- Copy this text:

2.- Translate these words: Speed of light: Refraction of light: Converging lenses:

Reflection of light: Reflected ray: Angle of incidence:

Incident ray: Diverging lenses: Angle of reflection:

3.- There are 150,000,000 km from the Sun to the Earth. How many seconds does the light of the Sun need to arrive to the Earth?

4.- Label this picture:

5.- On this irregular surface, the green lines represent light rays. a) Do you think ‘the incident angle’ and ‘the reflected angle’ are equal in A, B, and C?

On this irregular surface, the green lines represent light rays, and the red lines represent the normal in every situation. b) Do you think ‘the incident angle’ and ‘the reflected angle’ are equal in A, B and C?

6.- Do you think the rule ‘‘incident angle = reflected angle” is true in all cases? Why?

7.- What are the differences between both pictures?

8.- What is the rule of the reflection of light:

9.- In this picture, S1, S2, and S3 represent little holes in the wall. If the light moves in a straight line (yellow line) and collides into the wall, why can the last wall be illuminated?

Light

Walls 10.- Complete these diagrams about the reflection of light:

PROPERTIES OF LIGHT  Refraction of light: Light is refracted when it passes from one medium to another medium which has a different density. In this situation, instead of bouncing back, light bends at the boundary between the two media

Lenses are discs made of glass or plastic with one or two curved faces. There are two types: - Converging lenses: They are thicker at the centre than at the edges. They concentrate the rays of light. Example: a magnifying glass. - Diverging lenses: They are thicker at the edges than at the centre. They disperse the rays of light. Example: the glasses of a near-sighted person. NAME:_________________________________________ DATE:__________ 2º ESO___ (Bilingual) 1.- Copy the text

2.- Translate: Refraction of light: Angle of refraction: Converging lenses: Ray of light: Diverging lenses: Angle of incidence: 3.- Look at the picture above. Do you think ‘angle of incidence is equal to angle of refraction? Why?

4.- What does each letter represent? a= e b=

A= B=

c=

C=

d=

D=

e= E= 5.- What are the differences between ‘reflection’ and ‘refraction’ of light?

6.- a) What are lenses? b) What types of lenses are there? 7.- Complete these diagrams about the refraction of light:

8.- You cannot see the lenses. But label ‘convergent lens’ or ‘divergent lens’ according what you know. L E N S

L E N S

L E N S

L E N S

9.- One ray of light passes through two lenses. What is its trajectory? a) b)

10.- Which type of lens is each picture.

L E N S

L E N S

NAME:_________________________________________ DATE:__________ 2º ESO___ (Bilingual) HOW CAN EYES SEE COLORS? Visible light waves are the only electromagnetic waves visible to the human eyes. Eyes can see these waves as the colours of the rainbow. Each colour has a different wavelength and your retina can distinguish these different wavelengths. Then your brain interprets this information as colours. 1.- Copy this information:

2.- Translate these words: Eye: Visible light: Wave: Colors (or colours): Wavelength: Electromagnetic waves:

Brain: Retina: Rainbow:

3.- The range of electromagnetic spectrum is very wide. Each wavelength is received by a special receiver. Match each receiver with its correspondent wavelength. Electromagnetic Spectrum

Gamma-rays X-rays Ultraviolet-rays

Visible spectrum

Infra-red Microwave

Long-waves

4.- What are the visible light waves?

5.- Label the picture below using the pictures to the right to help you:

6.- What part of your eye can distinguish the different wavelengths? 7.- What organ interprets the information that your eyes receive? 8.- Hyperopia is a defect of the eye. The images are formed behind the retina. What kind of lens corrects this defect? L E N S

9.- Myopia is a defect of the eye. The images are formed in front of the retina. What kind of lens does correct this defect?

L E N S 10.- Match with arrows pictures and words:

Myopia

Miopía

Hyperopia

Hipermetropía

NAME:_________________________________________ DATE:__________ 2º ESO___ (Bilingual) WHAT IS A SOUND? Sound is a form of mechanical energy which is produced by the vibration of an object. Sound travels in waves through solids, liquids and gases. It cannot travel in a vacuum. The speed of sound depends on the media: it is 340 m/s in air, 1,500 m/s in water and 5,130 m/s in iron. The qualities of sound are:  Intensity: Sounds can be loud or soft, depending on the amplitude of the sound wave. The intensity of sound is measured in decibels (dB).  Pitch: Sounds can be high or low depending on the frequency of their waves. It differentiates the high and low notes of the same intensity, produced by a musical instrument. Pitch is measured in Hertz (Hz).  Tone: It allows us to identify the source of a sound which has the same frequency and intensity. Different instruments can be identified by their tone 1.- Copy the text:

2.- Translate these words Sound: Pithc:

Intensity: Tone;

3.- What is intensity of a sound?:

4.- What is pitch of a sound?

5.- What is tone of a sound?

Decibel: Frecuency:

6.- Match with arrows: Sound

allows us to identify the source of a sound.

Intensity

helps us distinguish between low and high sounds.

Pitch

depends upon the amplitude of the waves.

Tone

is produced by the vibration of an object.

7.- Label with ‘intensity’, ‘pitch’ and ‘tone’.

8.- This machinery drives pillars into the river bottom. Three people hear the sound. Person A is 2 km away and hears the sound through the air. Person B is 2 km away underwater and hears the sound through the water. Person C is 2 km away in the bank; he has the ear on one rock and hears the sound through the solid rock.

a) b) c) d) e) f)

What is the correct answer?: The three people hear the sound at the same time. These people hear the sound in this order: the first is A, the second is B and the third is C. These people hear the sound in this order: the first is B, the second is A and the third is C. These people hear the sound in this order: the first is C, the second is B and the third is A. These people hear the sound in this order: the first is C, the second is A and the third is B. Person C can not hear the sound.

9.- You see a lightning bolt and 10 seconds later you hear the thunder. How far away is the storm?

10.- You hammer a large piece of iron. How long does it take for the sound to travel 1 km? a) If the sound is transmitted in the air: b) If the sound is transmitted in the water: c) If the sound is transmitted in the iron: d) If the sound is transmitted in the vacuum:

NAME:_________________________________________ DATE:__________ 2º ESO___ (Bilingual) HOW IS SOUND REFLECTED? Sound is reflected when a sound wave meets an obstacle. The sound wave bounces off and changes direction.  The reflection of sound is used in many different fields: - Ultrasonic waves are used to scan the inside of the human body. - Sonar uses the reflection of sound to detect objects at sea or measuring the depth of the ocean.  The reflection of sound produces two phenomena: - Echo: It is produced when a sound is reflected by an obstacle. The obstacle must be situated at least 17 meters away. Both the initial sound and the reflected sound are heard. Hard surfaces reflect sound better than soft surface. - Reverberation: It occurs when a sound is reflected by an obstacle that is situated less than 17 m away. The initial sound and the reflected sound are heard, but they are mixed. 1.- Copy this text:

2.- Translate these words: Sound reflected: Ultrasonic waves: Echo:

Reflexion of sound: Sonar: Ultrasonic waves:

3.- What is the difference between echo and reverberation?

4.- For what are ultrasonic waves used?

5.- For what is the sonar used?

6.- What does this picture represent?

7.- Match the words to the appropiate pictures:

Ultrasonic waves for medicine

Sonar

8.- Look at this solved problem and solve another similar: a) Problem: A ship sends a pulse of ultrasound and receives an echo 0.3 seconds later. If the speed of sound in water is 1500 m/s calculate its depth. Answer: speed = distance / time therefore ... distance = speed × time distance = 1500 × 0·3 = 450 m BUT this is the total distance travelled by the sound, so the depth is half of this. Depth = 450 / 2 = 225 m Be careful, when dealing with reflected sound (echoes) exam questions often try to trick you into using the total distance, not the one you want. b) Solve this problem: “A sonar sends a pulse of ultrasound and receives an echo 0.45 seconds later. Calculate the depth of the sea.

9.- How is the reflection of the sound?

10.- Match with arrows: Echo

50 m

Reverberation

16 m 10 m

NAME:_________________________________________ DATE:__________ 2º ESO___ (Bilingual) WHAT ARE LIGHT AND SOUND POLLUTION? An excessive amount of light and sound can have adverse effects.  Light pollution: It occurs when people and animals are exposed to constant strong light. Artificial light sources include street lamps, advertising displays, floodlights on football fields, etc. Some of the adverse effects can be: - The impossibility of seeing the night sky. - Resources and energy being wasted. - Migrating birds colliding with lighted buildings. - Plant habits changing.  Sound pollution: Sound or noise pollution occurs when people or animals are exposed to levels of sound that are stressful or damaging to their hearing. Noise is caused by road traffic, aircrafts, trains, industries and entertainment centres, such as bars and discotheques. How to reduce sound pollution: - Building can be insulated to keep out loud noises. - Aircraft flight paths can be diverted away from cities. - Traffic can be reduced in city centres. - Legislation can establish limits on the intensity of noise from entertainment centres. 1.- Copy ‘sound pollution’:

2.- Translate these words: The night sky: Sound pollution:

Migrating birds: Light pollution:

3.- What is light pollution?

4.- What is sound pollution?

5.- Write some adverse effects of light pollution

6.- How can we reduce sound pollution?

7.- Match with arrows

Light pollution

Sound pollution

8.- What can have adverse effects?

9.- Match with arrows:

Impossibility of seeing the night sky.

Resources and energy being wasted.

Migrating birds colliding with lighted buildings.

Plant habits changing.

10.- Match with arrows: Building can be insulated to keep out loud noises.

Aircraft flight paths can be diverted away from cities.

Traffic can be reduced in city centres.

Legislation can establish limits on the intensity of noise from entertainment centres.