LIGHT AND SIGHT; describing a process 1. Discuss the questions. a) White light can be separated into different colours. What are they? b) What is your favourite colour? c) Has your favourite colour changed as you have grown older? d) What colour clothes do you like to wear? e) Do you prefer light or dark colours? f) What do the different colours mean in our culture? g) Is it possible to change the speed of light – slow it down, speed it up, or even stop it? 2. Check what you know about light. Choose the best answer. a) The wavelength of visible light is A) 400 nm to about 790 nm B) 380 nm to about 760 nm C) 380 nm to about 780 nm D) 380 nm to about 750 nm b) The wave-particle duality means that A) light rays curve twice B) light exists either as waves or as particles C) light is difficult to measure D) light exists both as waves and particles c) The speed of light is A) 299 792 438 m/s B) 299 791 458 m/s C) 299 792 458 m/s D) 299 792 358 m/s e) A) About 40% of sunlight is visible B) About 50% of sunlight is visible C) About 60% of sunlight is visible D) About 70% of sunlight is visible f) An incandescent source produces light A) as a result of chemical reactions B) as a result of transparency C) as a result of reflecting sunshine D) as a result of being made very hot g) Fireflies produce light A) because they carry tiny lanterns B) because they reflect moonshine C) due to some chemicals D) due to an inert gas inside their bodies h) You can see an object A) because light rays are dispersed from it B) because light rays are reflected from it C) because light rays are refracted D) because light rays are magnified i) Refraction is A) a very dark shadow B) a correction in the light beam direction C) a change in the light beam direction D) a calculation of fractions j) Polarization is A) a polar bear hunt B) a polar expedition of MU researchers to the South Pole C) the process of light orientation into one plane D) orientation according to the polar star k) Dispersion is A) a light shower B) a heavy rain C) a kind of Persian cat D) the separation of light into colours I. What is Light? Read the text about light and complete it with the missing parts of sentences A-H. There is one phrase too many. to propagate - přenášet, šířit (se) to hold sway - (to be master, to rule) vládnout, kralovat A. called photons B. contained in each photon C. detected by the human eye D. as demonstrated in the dual slit experiment E. which is the color of the light F. changing electric and magnetic fields G. which is the brightness of the light H. speeding those particles Light is simply a name for a range of electromagnetic radiation that can be 1. ____. What is electromagnetic radiation, then? Electromagnetic radiation has a dual nature as both particles and waves. One way to look at it is as 2. ____which propagate through space, forming an electromagnetic wave. This wave has amplitude, 3. ____, wavelength, 4. ____, and an angle at which it is vibrating, called polarization. This was the classical interpretation, crystallized in Maxwell's equations, which held sway until Planck, Einstein and others came along with quantum theory. In terms of the modern quantum theory, electromagnetic radiation consists of particles 5.____, which are packets ("quanta") of energy which move at the speed of light. In this particle view of light, the brightness of the light is the number of photons, and the color of the light is the energy 6.____. Which interpretation is correct? Both of them, actually. It turns out electromagnetic radiation can have both wave-like and particle-like properties 7. ____. II. Fluorescent lamps Read the text and underline the correct words. The fluorescent lamp is a sealed 1 (cylindrical / circular) glass tube that 2 (contains / consists) mercury at high pressure and electrodes at either ends of the tube. Sometimes a small amount of inert gas, such as argon, is placed in the tube. A phosphor powder 3 (skirts / coats) the inside of the glass. When the lamp is turned on, the current 4 (swims/flows) through the electrical circuit to the electrodes, which shoot electrons into the mercury vapour causing it to 5 (emit / emerge) a bluish light and ultraviolet radiation. We are unable to see the radiation but, when it hits the phosphor powder in the glass tube, it causes the emission of 6 (visible / seeable) light. These lamps do not produce much heat. 7 (Incandescent / Non-candescent) light bulbs glow because the filament is 8 (heated / heating) to a very high temperature. So a lot of energy is wasted as heat. Therefore fluorescent lamps are more 9 (economical / economic) than conventional light bulbs, even though the initial installation 10 (price / cost) of the fluorescent lamp is higher. III. Filament lamps Read the text and label the diagram. A filament lamp is an incandescent source of light, that is, it gives off light because it is very hot. The filament light bulb has a very thin tungsten filament coil, which is connected to electrical foot contacts via two stiff pieces of support wire. The support wires are enclosed in insulation at the base of the glass mount. The filament is enclosed in a glass case or bulb filled with an inert gas such as argon, and is fixed on a glass mount so that it sits in the middle of the bulb. When the bulb is connected to a power supply, an electric current passes through the tungsten filament. This makes the filament heat up to 2500 °C, at which point the tungsten glows white hot and emits light and heat. The heat is wasted energy since it produces no illumination. At these high temperatures the metal tends to evaporate and become condensed on the sides of the bulb, gradually darkening it. The inert gas in the bulb slows down this process and prevents oxidation of the tungsten which would happen if air was used to fill the bulb. Some bulbs have a screw thread to allow them to be securely fixed into a lamp. IV. LED LAMPS - how does LED light work? Listen to the recording and complete the table with most suitable information. Use one word only per each gap, unless stated otherwise. https://www.youtube.com/watch?v=u4L8gfzi3sE 1.What any LED is made up of 3 main _____ 2. Between an anode and a cathode a semiconductor _____ 3. The basis of an LED operation ______ 4. Determines the colour of the LED light semiconducting ____ 5. Most common use of LEDs ______ 6. The problem with using LEDs as a light source amount of ______________ (2 words) 7. The example of a less efficient light source mentioned ______ light bulbs 8. Absorbs heat to reduce an LED’s depreciation ________________ (2 words) V. DESCRIBING A PROCESS These points are commonly covered in a process description: Sequence Method Position Purpose Go over the texts about fluorescent and incandescent lights and find ways of wording the above points. VI. LED LAMPS Combining some information from the listening and the diagram below describe a process of generating light by an LED. Výsledek obrázku pro how LED works http://www.udaipurtalents.com/technical-learning/how-led-works Homework: The effect of different types of material on light Read the text and then label the three pictures. Opaque materials and objects block the passage of light, that is, they do not allow any light to pass through them, so it is impossible to see through them to objects on the opposite side. However, not all materials are opaque. Transparent materials allow light to pass through completely. As a result, it is easy to see things clearly on the other side of a transparent object. Clear glass and plastic wrap are examples of materials that are transparent. Translucent materials on the other hand only allow some light to pass through them, so it is difficult to see objects on the other side clearly. Examples of materials that are translucent are tracing paper, grease paper and frosted glass. Grammar revision: Reporting. Complete the second sentence so that it has a similar meaning to the first sentence, using the word given. Do not change the word given. Use between two and five words, including the word given. 1. “You put that frog on my chair, didn’t you, Charlie?” said Sally. of Sally ………………………………………………………….that frog on her chair. 2. “Stop misbehaving or you’ll be sent to the head,” the teacher said to Johnny. warned …………………………………………………………………………………… 3. At the interview, Kate was asked how well she had done in her exams. did The interviewer asked Kate: “How well ………………….in your exams?” 4. “Please try to stay awake during the lesson,” the teacher told them. urged The teacher ……………………………………………….asleep during the lesson. 5. Susan denied wasting her time at school when she was younger. said Susan …………………………………………….her time at school when she was younger. 6. “Have you tidied up the science lab?” the headmaster asked them. tidied The headmaster wanted to know …………………………………………in the science lab. 7. “I’ m sorry, I’ve forgotten my homework,” Nicholas said. apologized Nicholas……………………………………………………………. his homework. 8. Stephen told me he would see me the next day at the lecture. see “I…………………………………………………………..at the lecture,” Stephen said. Sources: Milada Pavlovová a Agnieszka Suchomelová http://library.thinkquest.org Kelly, Keith (2007) Science; MacMillan https://www.youtube.com