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Summary In this interactive workshop, explore visible light and how engineers and scientists use light to help us. Pupils explore burning different metals and how the excitation of electrons produces different wavelengths of light from these. They investigate how white light can be split and how the concentrated wavelengths of light from lasers can be used in engineering. Pupils then investigate how light can be used for entertainment, investigating 3D images. They are then challenged to create their own 3D animation using a praxinoscope. Copyright Teachers may reproduce the following materials without infringing copyright, so long as copies are made for use in their own schools. The permission of Techniquest must be obtained before reproducing these materials for any other purpose. Acknowledgements This workshop has been developed with support from the Royal Academy of Engineering. Thanks to the pupils and teachers of Newport High School, Pontypridd High School and West Monmouth Comprehensive School for their support and ideas. 2
UV Lava Lamp You may have seen lava lamps used as a way of lighting rooms and creating atmosphere. In this activity you can make a version of the lava lamp that does not require mains power. Using simple household items, including vegetable oil, Alka Seltzer tablets and tonic water, watch the chemical reactions create blobs of colour that look like a real lava lamp. What you need: Round-bottomed flask Vegetable oil Tonic water Effervescent tablet (such as for headaches) UV lamp What you do: 1. Pour the vegetable oil into the flask so that it is about half full. 2. Fill the other half of the flask with tonic water, leaving about 5cm from the top. 3. What do you notice? 4. Switch the UV light on and switch the rest of the lights off. 5. What you notice? 6. Break the effervescent tablet into two. Drop half into the flask. 7. What do you notice? Why does this happen? 3
What about the science? When the tonic water is added to the bottle, it sinks below the vegetable oil. After a few minutes, you will see that the tonic water lies at the bottom of the flask with the vegetable oil on top. This is because the oil is less dense than the water. When the UV lamp is switched on, the tonic water fluoresces. This is because of the quinine in the tonic water. The quinine absorbs the light photons from the UV lamp and releases photons of a different wavelength. These emitted photons glow blue or green under the UV lamp. Quinine fluoresces even in small quantities. When the effervescent tablet is dropped into the flask, it sinks. As it sinks below the vegetable oil, it mixes with the tonic water and begins dissolving. The tablet contains an acid and an alkali that react with the water to form carbon dioxide gas. The gas is less dense than the tonic water and the vegetable oil, so it rises in bubbles. These bubbles take some of the tonic water with them. When the bubbles reach the surface, they pop and the tonic water they were carrying sinks to the bottom again, because it is denser than the oil. If this reaction occurs when the UV lamp is switched on, the bubbles containing the tonic water will fluoresce blue or green, creating a lava lamp effect. Now you understand the science, try it again with the other half of the tablet. 4
Uses of UV: Exposure to UVB rays stimulates the production of vitamin D. UVB is absorbed by the glass in windows and so people need direct exposure to get the benefit. However, too much exposure to UVB can cause skin cancer, so a balance is needed. Newborn babies suffering from jaundice (caused by an excessive amount of bilirubin) are given short exposure to UV light as a cure. UV rays inhibit bacteria and viruses, and so they are useful when hanging washing out to dry or when sterilising medical equipment. Astronomical objects can be more easily observed using UV radiation. The hotter the object, the more UV it emits. By analysing the UV radiation from these objects, we can gain a deeper understanding of their temperature and chemical composition. Many documents rely on UV light as part of their security. Drivers licences, passports and bank notes contain elements that are invisible to the naked eye, but fluoresce under UV light. The number on the face of a bank note will fluoresce if you hold it under a UV light. This is one of many features on bank notes which are designed to make counterfeiting much more difficult. Fluorescence also occurs in nature. Rocks and minerals fluoresce under UV light. Geologists and engineers use UV lights to search for minerals and ores at night, as they are easier to find. 5
Exploring Refraction Try this simple experiment. What you need: A glass of water A straw What you do: Place the straw in the glass of water. Now look at the straw through the side of the glass. What do you notice? The straw seems to bend in the water. This effect is called refraction. The straw is not bending. The light is! How does this happen? We can see objects because light from a source (such as ceiling lights or the Sun) bounces off the object and into our eyes. Light travels in a straight line. Sometimes, light can be bent. If light is travelling from one medium (such as through the air) to another medium (such as water) which has a different density, the light is bent (or refracted). So why does the straw look bent? Light bouncing off the part of the straw above the water travels straight to the eye through the air. Light bouncing off the part of the straw that is under the water travels to your eye first through the water and then through the air. As the light move from the water to the air there is a change in density. This causes the light to bend, reaching the eye at a slightly different angle, causing the straw to look bent. 6
Investigate Refraction Refraction can create some fantastic optical illusions that can be used to trick your friends and family. Can you make arrows change direction without touching them? What you need: An empty glass A card with two horizontal arrows on it A jug of water. What you do: Show a friend the card with the arrows on it. Challenge them to change the direction of the arrows without touching the card. Hand them the glass and the jug of water and tell them these can be used to help them. As an extra challenge, can they just change the direction of one arrow? How to solve the challenge: Stand the card with the arrows on it directly behind the empty glass. Pour water into the glass up to the top of the first arrow. Look through the water at the arrows. The bottom arrow will appear to have changed direction. Continue pouring water to fill the glass. Now the top arrow will also have changed direction. 7
What about the science? The reason for this effect is refraction (bending light). As the glass fills up with water above the level of the arrow, the arrow appears to change direction. This effect is created as the light bounces from the arrow through the water into the less dense air and then into your eyes. Whenever light passes out of one medium into another, it refracts (or bends). But why does the arrow appear to be reversed? Think of the glass of water as if it is a magnifying glass. When light goes travels a magnifying Glass of water viewed from above Light ray glass the light is bent toward the centre (known as the focal point). Beyond the focal point the image appears to reverse because the light that was on the right side is now on the left and the left on the right. Focal point Uses of refraction in engineering: Seismic refraction is used to find out the different rocks and soils that make up the geologic layers below an area of ground. Artificial seismic waves are sent through the ground and the way the waves travel is recorded using a seismograph. The seismic waves travel with different velocities through different types of rock and soil. In addition, the seismic waves are refracted (or bent) as they travel through one type of rock or soil into another. Geological engineers then interpret this data to identify the rocks and soils below the surface, to determine if construction can commence at that site. 8
Curriculum Links: KS3 Science SKILLS Communication Pupils are given opportunities to: Search systematically for, process and analyse information for a specific purpose, including ICT as appropriate. Communicate logically by speech, writing, drawings, diagrams, charts, tables, bar charts, line graphs, videos and ICT packages using a wide range of scientific vocabulary, terms, symbols and conventions. Enquiry Planning Pupils are given opportunities to: Make predictions using previous knowledge, understanding and preliminary work. Use a range of options as to where and how to find relevant information and ideas the equipment and techniques required for the enquiry. Developing Pupils are given opportunities to: Identify, describe and explain trends, patterns and relationships. Use scientific prior knowledge to explain links between cause and effect when concluding. Consider whether there is sufficient information to enable firm conclusions to be drawn, taking account of uncertainties and anomalies. Identify and assess bias and reliability. Consider others views to inform opinions and decisions. Reflecting Pupils are given opportunities to: Identify the learning/thinking strategies they have used. Link the learning to dissimilar but familiar situations, within and outside school. RANGE How things work Pupils are given opportunities to study: How familiar devices/machines work by using electricity, light, sound and other energy transfers. Technologies under development, which may lead to more efficient use of energy resources or using them in new ways, e.g. hydrogen-powered cars, using cooking oil/gasohol, as replacements for diesel/petrol. 9