Page:SELECTED ESSAYS of Dr. S. S. KALBAG.pdf/155

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they flow from -ve to +ve, (high pressure of electrons to shortage of electrons). How do they flow? We tell students sitting on classroom benches that one of them is an electron, and the other two are nucleus. The student in front walks off creating a "vacancy". The student behind moves into this vacancy and so on until the "vacant" seat moves to the back of the class, while the electrons move to the front. Thus the same process can be seen as electrons moving in one direction and positive charges (holes) moving in the opposite direction. Similarly, we have illustrated 3-phase electricity by 3 boys running in a circle, representing the rotor in the generator. 3. The concepts of force, strength and work are a bit easier to teach as there are many applications of these in their practical work. To illustrate, we explain why trusses are based on triangles and why one strengthens a right angle joint by a diagonal. Also they calculate the work done in many of their practicals e.g. pumping water. 4. The simple machines described in science lessons do not make sense in terms of the leaning of "machine" in everyday language. We therefore like to bring one common machine, say the bench drill and show how it is a combination of the simple machines as described in the book viz. the lever, the screen, gears etc. Then the student can go round the workshop and examine any other machine and identify the simple machines used there. 5. Genes, heredity and evolution. The concept of probability as applied to genetics, stresses that what is a matter of chance in small numbers, becomes a certainty when dealing with large numbers. This is best illustrated through a game. Rural Development Through Education System 142