Dein Suchergebnis zum Thema: have/"<b/""

At least two of the following rays are needed to construct the image: • Ray from the object parallel to the optical axis (parallel ray) • Ray from the object through the focal point of the lens (focal ray) • Ray from the object through the central point of the lens (central point ray). The central point ray passes through the lens without changing direction. The parallel ray passes through the focal point on the other side of the lens, and the focal ray becomes the parallel ray. Note: The imaging equation is also frequently known as the “lens equation. Information and ideas: What are lenses needed for?
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Light quanta impinging on a semiconductor generate conduction electrons at higher potential due to the internal photo effect. From there they can flow away via the external circuit and can be used. This effect is dependent on the energy of the photons and on the semiconductor material. An animation shows how the electric current flows in the photocell. Graphics explaining the internal photo effect in a semiconductor and the energy diagram of the solar cell can also be displayed. Information and ideas: Where are photocells used for producing electric power? What efficiency can be attained?
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In this process, pressure is applied to salty water, pressing it against a semi-permeable membrane with extremely small pores. The pore size allows water molecules of around 0.28 nm to pass through, while salt ions are kept back. (Although salt ions in and of themselves are smaller than water molecules, in this case they are significantly larger due to their bonded hydration shell). This process is used in large plants around the world to desalinate seawater in areas with shortages of drinking water. Information and ideas: In addition to reverse osmosis, there are other membrane filter procedures that differ in the pore size of the membrane: • Microfiltration • Ultrafiltration • Nanofiltration
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Membrane filters consist of a microporous material. During filtration of water suspended particles above a certain size are retained while smaller particles can pass through the membrane unimpeded. Apart from typical applications of the individual filter types, this tabular overview also lists the main parameters. Plastic is generally used as the filter material, although metal and ceramic membranes are also possible in principle. Depending on the size of the particles to be separated out and the pore size of the membrane the filtration process is referred to as microfiltration, ultrafiltration, nanofiltration or reverse osmosis. The smaller the pores are, the greater the applied pressure difference has to be in order to force the water through the membrane. Information and ideas: Information on the individual filtration processes for further study can be found in the “Guideline for water treatment on the media portal of the Siemens Stiftung.
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The video starts with a brief introduction to the greenhouse gas carbon dioxide. A graphic then illustrates the functional principle of the greenhouse effect. Two things become clear: firstly, that life on Earth would not be possible without the greenhouse effect; secondly, that the human-induced greenhouse effect is having a harmful effect on the Earth. Carbon dioxide produced by humans is named as the cause of this harmful effect. The video ends on the following question for further study, “… and where does this additional CO2 come from? Information and ideas: This video sequence can be followed, for example, by a detailed discussion of harmful greenhouse gases. This video is an excerpt from the teaching DVD, „Das grüne Paradoxon – Warum die Erde wärmer wird.
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Evaporation is vital for plants. Its leaves are covered on all surfaces by epidermal cells, which are protected by a layer of wax (cuticle) on the outside, making it hard for water vapor (as well as for oxygen and CO2) to permeate the surfaces. Gas is exchanged with the environment through stomata. These stomata consist of two bean-shaped guard cells, which regulate the gas exchange of the leaf and thus can also control the evaporation rate in the range of two orders of magnitude. Information and ideas: The microscopic photo originates from an electron microscope.
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Evaporation is one element in the water cycle. Evaporation causes vapor to rise to higher, cooler layers of air, where it forms clouds of small water droplets or ice crystals and then falls to the surface again. Information and ideas: Other animations on evaporation can be found under this term. Students should enter the stations of the principle of ecaporation. The worksheet can be used during in the work phase and in the repetition phase to record the results.
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The two magnetic separation procedures are used, for example, to sort residual waste. The text provides information about the kinds of materials the respective procedure is suitable for and the physical principle each procedure is based on. Sample applications of these principles that the students are familiar with from class are mentioned. The way the two procedures work is explained and technical implementation for separating residual waste is outlined. Information and ideas: The example of sorting residual waste also works well for learning about other physical separation procedures, such as sifting (separation by grain size) and wind sifting (separation by density).
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The students will measure the pH value of water as well as of water with citric acid and water with washing soda. They will learn the terms alkali and acid. The instructions first include a photo and a list of the required apparatus and materials. Text and pictures explain the preparations for the experiment step by step. Then several assignments are presented: The students should express their guesses, conduct the experiment, and note down their observations. Information and ideas: • Observe the safety information in these instructions as well as in the teacher information related to the experiment and discuss them with your students. • Also observe the applicable safety guidelines for your school.
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The teaching methods specify the learning prerequisites for completing the task on the worksheet. The students should already know that plants release most of the water that they absorb through their roots through evaporation via their leaves. The scientific background on the task and possible variations are provided. The six incremental hints for the task are provided with the corresponding answers. They are also available as a separate ready-to-print medium named “Not all shade is the same (hints for printing)” or as an interactive medium named “Not all shade is the same (interactive hints)” on the media portal of the Siemens Stiftung.
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