department of school education govt. of tamilnadu bridge course class-viii- science
TRANSCRIPT
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Department of School Education Govt. of Tamilnadu Bridge Course
Class-VIII- Science
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Govt. of TamilnaduDepartment of School Education
Bridge Course 2011-2012
Class VII
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I.HISTORY OF THE ATOMI.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
ATOMAATOMA
(greek for indivisible)
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HISTORY OF THE ATOMHISTORY 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
ATOMSATOMS
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HISTORY OF THE ATOMHISTORY OF THE ATOM
1898 Joseph John Thompson
found that atoms could sometimes eject a
far smaller negative particle which he
called an
ELECTRONELECTRON
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HISTORY OF THE ATOMHISTORY 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
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HELIUM ATOM
+N
N
+-
-
proton
electron
neutron
Shell
What do these particles consist of?
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ATOMIC STRUCTUREATOMIC STRUCTURE
Particle
proton
neutron
electron
Charge
+ ve charge
-ve charge
No charge
1
1
nil
Mass
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ATOMIC STRUCTUREATOMIC 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
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II. CARBON-*Diamond and Graphite.
*each carbon atom is linked with other carbon atoms with strong network like bonding.
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GRAPHITE-carbon atom in flat layers, hexagonal ring shaped. Bonding between the
layers are flexible hence graphite is used as lubricant.
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DIAMOND
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FULLERINS-on heating graphite with very high temperature this fullerin is produced.
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III.Metals and non-metals
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The Periodic Table is divided into….
Metals
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and non-metals
The Periodic Table is divided into….
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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)
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Non-metals….
• Have low melting and boiling points.
• Are brittle.
• Do not conduct heat or electricity well.
(except carbon)
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Different metals are suitable for different jobs.
Gold, silver and platinum are very unreactive but very malleable - making them suitable for jewellery
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Copper is malleable, ductile and it conducts heat and electricity well.
It is also unreactive making it suitable for holding and carrying water.
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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.
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Iron ore is common and iron itself is very strong.
It can be moulded into many shapes
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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.
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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.
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IV.LIGHT
1) Properties of light2) Reflection3) Colours4) Refraction
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Part 1 – Properties of Light
• Light travels in straight lines:
Laser
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• Light travels VERY FAST – around 300,000 kilometres per second.
At this speed it can go around the world 8 times in one second.
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• 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.
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• We see things because they reflect light into our eyes:
Homework
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• Luminous and non-luminous objects
A luminous object is one that produces light.
A non-luminous object is one that reflects light.
Luminous objects Reflectors
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• Shadows
Shadows are places where light is “blocked”:
Rays of light
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Properties of Light summary
1) Light travels in straight lines2) Light travels much faster than sound3) We see things because they reflect light into
our eyes4) Shadows are formed when light is blocked by
an object
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Part 2 - Reflection• Reflection from a mirror:
Incident ray
Normal
Reflected ray
Angle of incidence
Angle of reflection
Mirror
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• The Law of ReflectionThe Law of Reflection
Angle of incidence = Angle of reflectionAngle of incidence = Angle of reflection
In other words, light gets reflected from a surface at angle it hits it.
The same !!!
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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
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Using mirrors• Two examples:
1) A periscope
2) A car headlight
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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.
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The colours of the rainbow:
• Red• Orange• Yellow• Green• Blue
• Indigo• Violet
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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
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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
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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
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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
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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
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Load Arm
Fulcrum
LoadEffort
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.
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Class 1 Class 2 Class 3
Click on the correct Lever classification for the tool pictured below.
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Click on the correct Lever classification for the tool pictured below.
Class 1 Class 2 Class 3
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Click on the correct Lever classification for the tool pictured below.
Class 1 Class 2 Class 3
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Click on the correct Lever classification for the tool pictured below.
Class 1 Class 2 Class 3
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Click on the correct Lever classification for the tool pictured below.
Class 1 Class 2 Class 3
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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
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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
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Single Fixed Pulley
This pulley provides the user Directional Advantage, allowing someone to pull down to lift the load up
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Inclined Plane Wrapped around post = Screw
Screw-activityShall we do this?
A Screw is really an Inclined Plane wrapped around a center post.
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VII. OVER VIEW OF STEM- open Vascular bundle(cambium present in between xylem and
phloem)
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CS OF STEM-vascular bundles arranged in a ring.
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CS OF STEM-cortex outside the vascular bundle. pith in the center
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CS OF STEM-xylem endarch (protoxylem [small] ) towards center.
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VIII. ROOT
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CS OF ROOT-Xylem exarch, xylem and phloem in same radius
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CS OF ROOT
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IX. TS OF LEAF-note the gaurd cells in epidermis in between two gaurd cells there lies stomata