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Department of School Education Govt. of Tamilnadu Bridge Course

Department of School Education Govt. of Tamilnadu Bridge Course

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Department of School Education Govt. of Tamilnadu Bridge Course

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  1. Department of School Education Govt. of Tamilnadu Bridge Course Class-VIII- Science

  2. Govt. of TamilnaduDepartment of School EducationBridge Course 2011-2012Class VII

  3. I.HISTORY OF THE ATOM Democritus develops the idea of atoms 460 BC he pounded up materials in his pestle and mortar until he had reduced them to smaller and smaller particles which he called ATOMA (greek for indivisible)

  4. HISTORY OF THE ATOM John Dalton 1808 suggested that all matter was made up of tiny spheres that were able to bounce around with perfect elasticity and called them ATOMS

  5. HISTORY OF THE ATOM Joseph John Thompson 1898 found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON

  6. HISTORY OF THE ATOM Ernest Rutherford 1910 oversaw Geiger and Marsden carrying out his famous experiment. they fired Helium nuclei at a piece of gold foil which was only a few atoms thick. they found that although most of them passed through. About 1 in 10,000 hit

  7. HELIUM ATOM Shell proton N + - + N - neutron electron What do these particles consist of?

  8. ATOMIC STRUCTURE Particle Charge Mass proton + ve charge 1 neutron No charge 1 electron -ve charge nil

  9. ATOMIC STRUCTURE Atomic number the number of protons in an atom Atomic mass the number of protons and neutrons in an atom number of electrons = number of protons

  10. II. CARBON-*Diamond and Graphite.*each carbon atom is linked with other carbon atoms with strong network like bonding.

  11. GRAPHITE-carbon atom in flat layers, hexagonal ring shaped. Bonding between the layers are flexible hence graphite is used as lubricant.

  12. DIAMOND

  13. FULLERINS-on heating graphite with very high temperature this fullerin is produced.

  14. III.Metals and non-metals

  15. The Periodic Table is divided into…. Metals

  16. The Periodic Table is divided into…. and non-metals

  17. Metals all have similar physical properties… • They have high melting and boiling points (except mercury) • They conduct electricity and heat. • They have a high density. • They are shiny (lustrous). • They are malleable (can be moulded) • They are ductile (can be stretched)

  18. Non-metals…. • Have low melting and boiling points. • Are brittle. • Do not conduct heat or electricity well. • (except carbon)

  19. Gold, silver and platinum are very unreactive but very malleable - making them suitable for jewellery Different metals are suitable for different jobs.

  20. Copper is malleable, ductile and it conducts heat and electricity well. It is also unreactive making it suitable for holding and carrying water.

  21. Aluminium is a reactive metal, but it forms a coating of very stable aluminium oxide. This, together with its lightness and malleability gives it many uses from window frames to insulation foil.

  22. Iron ore is common and iron itself is very strong. It can be moulded into many shapes

  23. Unfortunately iron is quite brittle (for a metal) and also oxidises (rusts) easily. As it forms, iron oxide constantly flakes away exposing more of the iron underneath. Remember: Only iron oxide is called rust. No other metal rusts!

  24. To prevent this happening, iron is often covered with a thin layer of zinc. Like aluminium, zinc oxidises to form a stable coating of zinc oxide which protects the iron underneath it. This is called galvanising.

  25. IV.LIGHT • Properties of light • Reflection • Colours • Refraction

  26. Laser Part 1 – Properties of Light • Light travels in straight lines:

  27. Light travels VERY FAST – around 300,000 kilometres per second. At this speed it can go around the world 8 times in one second.

  28. Thunder and lightning start at the same time, but we will see the lightning first. • Light travels much faster than sound. For example: • 2) When a starting pistol is fired we see the smoke first and then hear the bang.

  29. We see things because they reflect light into our eyes: Homework

  30. A luminous object is one that produces light. A non-luminous object is one that reflects light. • Luminous and non-luminous objects Luminous objects Reflectors

  31. Rays of light Shadows are places where light is “blocked”: • Shadows

  32. Properties of Light summary • Light travels in straight lines • Light travels much faster than sound • We see things because they reflect light into our eyes • Shadows are formed when light is blocked by an object

  33. Part 2 - Reflection • Reflection from a mirror: Normal Reflected ray Incident ray Angle of reflection Angle of incidence Mirror

  34. Angle of incidence = Angle of reflection • The Law of Reflection In other words, light gets reflected from a surface at angle it hits it. The same !!!

  35. Clear vs. Diffuse Reflection • Smooth, shiny surfaces have a clear reflection: Rough, dull surfaces have a diffuse reflection. Diffuse reflection is when light is scattered in different directions

  36. Using mirrors • Two examples: 2) A car headlight 1) A periscope

  37. Colour • White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow. We can demonstrate this by splitting white light with a prism: This is how rainbows are formed: sunlight is “split up” by raindrops.

  38. The colours of the rainbow: • Red • Orange • Yellow • Green • Blue • Indigo • Violet

  39. Adding colours • White light can be split up to make separate colours. These colours can be added together again. • The primary colours of light are red, blue and green: Adding blue and red makes magenta (purple) Adding blue and green makes cyan (light blue) Adding red and green makes yellow Adding all three makes white again

  40. Homework Seeing colour • The colour an object appears depends on the colours of light it reflects. For example, a red book only reflects red light: White light Only red light is reflected

  41. A pair of purple trousers would reflect purple light (and red and blue, as purple is made up of red and blue): Purple light A white hat would reflect all seven colours: White light

  42. Using coloured light • If we look at a coloured object in coloured light we see something different. For example, consider a football kit: Shirt looks red White light Shorts look blue

  43. Refraction Refraction is when waves ____ __ or slow down due to travelling in a different _________. A medium is something that waves will travel through. When a pen is placed in water it looks like this: In this case the light rays are slowed down by the water and are _____, causing the pen to look odd. The two mediums in this example are ______ and _______. Words – speed up, water, air, bent

  44. Levers&Pulleys

  45. Parts of a Lever Effort Load Load Arm Fulcrum A lever is a simple machine used to reduce the amount of effort it would take to lift a load or reduce the amount of effort needed to do work.There are 3 types of levers: Class 1, Class 2, and Class 3. The effort needed to lift a load is measured in Newtons.

  46. Click on the correct Lever classification for the tool pictured below. Class 1 Class 2 Class 3

  47. Click on the correct Lever classification for the tool pictured below. Class 1 Class 2 Class 3

  48. Click on the correct Lever classification for the tool pictured below. Class 1 Class 2 Class 3