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

2. Govt. of Tamilnadu Department of School Education Bridge Course 2011-2012 Class VII

3. I.HISTORY OF THE ATOM 460 BC Democritus develops the idea of atoms 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 1808 John Dalton 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 1898 Joseph John Thompson found that atoms could sometimes eject a far smaller negative particle which he called an ELECTRON

6. HISTORY OF THE ATOM 1910 Ernest Rutherford 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 + N N + - - proton electron neutron Shell What do these particles consist of?

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

9. ATOMIC STRUCTURE the number of protons in an atom the number of protons and neutrons in an atom Atomic mass Atomic number 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. and non-metals The Periodic Table is divided into….

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

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. Remember: Only iron oxide is called rust. No other metal rusts! 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.

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

25. IV.LIGHT 1)Properties of light 2)Reflection 3)Colours 4)Refraction

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

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. Light travels much faster than sound. For example: 1)Thunder and lightning start at the same time, but we will see the lightning first. 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. Luminous and non-luminous objects A luminous object is one that produces light. A non-luminous object is one that reflects light. Luminous objectsReflectors

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

32. Properties of Light summary 1)Light travels in straight lines 2)Light travels much faster than sound 3)We see things because they reflect light into our eyes 4)Shadows are formed when light is blocked by an object

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

34. The Law of Reflection The Law of Reflection Angle of incidence = Angle 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: 1) A periscope 2) A car headlight

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 all three makes white again Adding red and green makes yellow

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

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

46. Load Arm Fulcrum Load Effort Parts of a Lever 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.

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

49. Class 1 Class 2 Class 3

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

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

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

53. Levers can provide Mechanical Advantage by reducing the effort needed to lift a load. The closer the fulcrum is to the load, the less effort is needed to lift the load. The load does not move a great distance. E L F

54. Levers can be used to move loads farther if the fulcrum is placed close to the effort. In this situation more effort is needed to lift the load, but the load will move farther than if the fulcrum was closer to the load. F E L

55. Single Fixed Pulley This pulley provides the user Directional Advantage, allowing someone to pull down to lift the load up

56. Inclined Plane Wrapped around post = Screw Screw-activity Shall we do this? A Screw is really an Inclined Plane wrapped around a center post.

57. VII. OVER VIEW OF STEM - open Vascular bundle(cambium present in between xylem and phloem )

58. CS OF STEM - vascular bundles arranged in a ring.

59. CS OF STEM - cortex outside the vascular bundle. pith in the center

60. CS OF STEM - xylem endarch (protoxylem [small] ) towards center.

63. VIII. ROOT

64. CS OF ROOT - Xylem exarch, xylem and phloem in same radius

65. CS OF ROOT

67. IX. TS OF LEAF -note the gaurd cells in epidermis in between two gaurd cells there lies stomata