Department of School Education Govt. of Tamilnadu Bridge Course

Class-VIII- Science

Govt. of TamilnaduDepartment of School Education

Bridge Course 2011-2012

Class VII

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)

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

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

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

HELIUM ATOM

+N

N

+-

-

proton

electron

neutron

Shell

What do these particles consist of?

ATOMIC STRUCTUREATOMIC STRUCTURE

Particle

proton

neutron

electron

Charge

+ ve charge

-ve charge

No charge

1

1

nil

Mass

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

II. CARBON-*Diamond and Graphite.

*each carbon atom is linked with other carbon atoms with strong network like bonding.

GRAPHITE-carbon atom in flat layers, hexagonal ring shaped. Bonding between the

layers are flexible hence graphite is used as lubricant.

DIAMOND

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

III.Metals and non-metals

The Periodic Table is divided into….

Metals

and non-metals

The Periodic Table is divided into….

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)

Non-metals….

• Have low melting and boiling points.

• Are brittle.

• Do not conduct heat or electricity well.

(except carbon)

Different metals are suitable for different jobs.

Gold, silver and platinum are very unreactive but very malleable - making them suitable for jewellery

Copper is malleable, ductile and it conducts heat and electricity well.

It is also unreactive making it suitable for holding and carrying water.

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.

Iron ore is common and iron itself is very strong.

It can be moulded into many shapes

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.

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.

IV.LIGHT

1) Properties of light2) Reflection3) Colours4) Refraction

Part 1 – Properties of Light

• Light travels in straight lines:

Laser

• Light travels VERY FAST – around 300,000 kilometres per second.

At this speed it can go around the world 8 times in one second.

• 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.

• We see things because they reflect light into our eyes:

Homework

• 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

• Shadows

Shadows are places where light is “blocked”:

Rays of light

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

Part 2 - Reflection• Reflection from a mirror:

Incident ray

Normal

Reflected ray

Angle of incidence

Angle of reflection

Mirror

• 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 !!!

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

Using mirrors• Two examples:

1) A periscope

2) A car headlight

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.

The colours of the rainbow:

• Red• Orange• Yellow• Green• Blue

• Indigo• Violet

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

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

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

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

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

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.

Class 1 Class 2 Class 3

Click on the correct Lever classification for the tool pictured below.

Click on the correct Lever classification for the tool pictured below.

Class 1 Class 2 Class 3

Click on the correct Lever classification for the tool pictured below.

Class 1 Class 2 Class 3

Click on the correct Lever classification for the tool pictured below.

Class 1 Class 2 Class 3

Click on the correct Lever classification for the tool pictured below.

Class 1 Class 2 Class 3

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

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

Single Fixed Pulley

This pulley provides the user Directional Advantage, allowing someone to pull down to lift the load up

Inclined Plane Wrapped around post = Screw

Screw-activityShall we do this?

A Screw is really an Inclined Plane wrapped around a center post.

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

phloem)

CS OF STEM-vascular bundles arranged in a ring.

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

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

VIII. ROOT

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

CS OF ROOT

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