Vegetable dyes, mineral dyes, animaldyes, synthetic dyes, basic dyes acid dyes.

Vegetable Dyes
The earliest dyes were of vegetable origin,
discovered by accidentally staining garments
with juices of fruits or plants. Vegetable dyes
are obtained from different parts of plants
such as leaves, flowers, fruits, pods, bark etc.
These vegetable dyes can be applied directly
or with different mordants.
● Indigo: Indigo (blue dye) is called
as the king of all natural dyestuffs.
It imparts blue colour. It is extracted
from the leaves of the leguminous
plant, Indigofera tinctoria. It is suitable
for dyeing cotton and wool.
● Indian Madder: It produces shades
of red on textile fabrics. It is used for
dyeing cotton and woollen fabrics. It is
extracted from roots of Rubia tinctoria.
● Turmeric: It produces shades of yellow
on fabrics. It is suitable for dyeing
cotton, silk and wool. The yellow dye
is extracted from the ground root
(rhizome) of turmeric plant (Curcuma
longa).
● Marigold: It is extracted from lemon or
orange coloured marigold (Calendula
officinalis) flower. It is suitable for
dyeing both silk and wool fibres.
● Henna: The dye is extracted from the
dried leaves of Henna plant, Lawsonia
inermis. It produces yellowish orange
colour. It is suitable for dyeing wool
and silk fibres.
● Tea: Leaves of tea plants (Camellia
sinensis) or tea powder is used to
extract dye. It produces different
shades of brown.
● Onion: The dye is extracted from the
outer most skin or peel of the onion
(Allium cepa). The onion skins if properly
dried can be used for one yearAnimal Dyes
Dyes extracted from certain insects and
invertebrates are called as animal dyes.
Various shades of red and purple were
obtained from animal origin. Cochineal,
Tyrian purple and Lac are the commonly
used animal dyes.
1. Cochineal
Cochineal dye is extracted from
the dried bodies of the female
red bug (Dactylopius coccus). It
produces crimson and scarlet
colours with mordants aluminium
and tin oxide. This dyestuff was
mostly used for dyeing wool and
silk. These dyes exhibit excellent
fastness properties.
2. Tyrian Purple
This dye is extracted from the sea
snails found in Mediterranean Sea.
The amount of dye produced was
very limited and therefore very
expensive. Hence, it is called Royal
purple.
3. Lac Dye
This dye is extracted from the fluid
secreted by the lac insect (Lauifer
lacca), which lives on the twigs of
the banyan trees and other varieties. It produces crimson and scarlet
colours. These dyes possess good
fastness to light and washing.
Animal dyes are also obtained from
murex snail (purple colour) and Octopus/
Cuttle fish (Sepia brown).
How invention of col

Mineral Dyes
Dyes extracted from mineral sources are
called as mineral dyes. Most widely used
mineral dyes are Iron, which produces
yellowish brown shades, chrome yellow,
prussian blue and manganese brown. The
dyes obtained from mineral sources may
be poisonous and hence are not being
used commercially

Synthetic Dyes
Dyes that are produced chemically are called
as synthetic dyes. These are classified based
on the chemical composition of the dye.
Direct Dyes
When a dye colours the fabric directly
without the help of any fixing agent,
the dye is said to be a direct dye. Direct
dyes are water soluble. They are easy to
produce, simple to apply and cheap in
cost of production and application. Direct
dyes are anionic in nature and have greater
affinity for cellulosic fibres. They are used
to dye cellulose fibres without a mordant
in bright shades and they produce a wide
range of colours. A levelling agent such
as sodium carbonate is added for even
dyeing. At the end of dyeing, exhaustion
agent such as salt (NaCl) is added which
helps the dye to leave the liquor and get
attached to the fibre. Some direct dyes
are used to dye wool, silk and nylon.
Direct dyes can be applied to wide variety
of textile materials such as apparel,
upholstery fabrics, draperies, linings
and automotive fabrics. Most direct dyes
have good fastness to light but poor wash
fastness.
Reactive Dyes
Dyes that react with the fibres and form
covalent bonds are called as reactive dyes.
They become an integral part of the fibre.
They are water soluble and are used to
dye cellulose, protein and polyamide
fibres. They produce full range of bright
shade across the spectrum. They exhibit
excellent wash fastness and good light
fastness properties. Dyeing of fibre with
reactive dyes involves 3 steps, namely
exhaustion of dye (NaCl or Glauber’s salt), fixation of dye (sodium carbonate or
sodium hydroxide) and washing off.

Basic Dyes
Basic dyes have cationic or basic groups
(positively charged) and hence they are
also known as cationic dyes. Basic dyes
react with the acidic groups present in
the fibres and form electrovalent bonds.
Basic dyes are soluble in alcohol but not
easily soluble in water. Basic dyes exhibit
brilliant shades of colour which is not
shown by other dye classes. Basic dyes are
suitable for dyeing wool, silk and acrylic,
but they have no affinity towards cellulosic
fabrics. Basic dyes are used along with a
mordant for fibres such as cotton, linen,
acetate, nylon and polyester. Basic dyes
show moderate light and wash fastness.
For dye preparation, the dyestuff is mixed
with equal amount of acetic acid followed
by warm water under constant stirring.
Acid Dyes
Water soluble dyes that require acid
(sulphuric, acetic, formic acid etc.,) in dye
bath to dye silk or wool are called as acid
dyes. These acid dyes are mostly sodium
salts of organic acids. When dissolved in
water, acid dyes produce negative ions
(anions or acidic groups) which react
with positive ions of protein fibres and get
attached to the fibre through electrovalent
bonds. Acid dyes are similar to direct
dyes however they cannot be applied to
cellulosic fibre due to slight variations in
structure. Acid dyes have greater affinity
for protein and polyamide fibres. They
posses very good fastness to washing
and good fastness to light. A large colour
range is available with acid dyes. They are
inexpensive.

APPLICATION S OF GAUSS LAW

Electric field due to any arbitrary charge
configuration can be calculated using
Coulomb’s law or Gauss law. If the charge
configuration possesses some kind of
symmetry, then Gauss law is a very efficient
way to calculate the electric field. It is
illustrated in the following cases.

Cases


(i) Electric field due to an infinitely long
charged wire
Consider an infinitely long straight
wire having uniform linear charge density
λ(charge per unit length). Let P be a point
located at a perpendicular distance r from
the wire . The electric field
at the point P can be found using Gauss law.
We choose two small charge elements
A1
and A2
on the wire which are at equal
distances from the point P. The resultant
electric field due to these two charge
elements points radially away from the
charged wire and the magnitude of electric
field is same at all points on the circle
of radius r. This is shown in the FigureSince the charged wire possesses

a cylindrical symmetry, let us choose a
cylindrical Gaussian surface of radius r and
length L as shown .
The total electric flux through this closed
surface is calculated as follows

applying Gauss law to the
cylinderical surface

Since the magnitude of the electric field
for the entire curved surface is constant, E istaken out of the integration and Qencl is given
by Q L encl = λ , where λ is the linear charge
density (charge present per unit length).

Here dA
Curved surface
∫ = total area of the curved
surface = 2πrL. Substituting this in equation

In vector form,

The electric field due to the infinite
charged wire depends on 1/
r
rather than 1 /

r2
.
The equation is true only for an
infinitely long charged wire. For a charged
wire of finite length, the electric field
need not be radial at all points. However,
equation for such a wire is taken
approximately true around the mid-point
of the wire and far away from the both ends
of the wire


(ii) Electric field due to charged infinite
plane sheet
Consider an infinite plane sheet of
charges with uniform surface charge
density σ (charge present per unit area).
Let P be a point at a distance of r from the
sheet as shown in the.

Since the plane is infinitely large, the
electric field should be same at all points
equidistant from the plane and radially
directed outward at all points. A cylindrical
Gaussian surface of length 2r and two flats
surfaces each of area A is chosen such that the
infinite plane sheet passes perpendicularly
through the middle part of the Gaussian
surface.
Total electric flux linked with the
cylindrical surface,

The electric field is perpendicular to
the area element at all points on the curved
surface and is parallel to the surface areas
at P and P′ . Then, applying
Gauss’ law,

Since the magnitude of the electric field
at these two equal flat surfaces is uniform,
E is taken out of the integration and Qencl is
given by Q A encl = σ , we get


The total area of surface either at P or P

Here n
 is the outward unit vector
normal to the plane. Note that the electric
field due to an infinite plane sheet of charge
depends on the surface charge density and is
independent of the distance r.
The electric field will be the same at any
point farther away from the charged plane.
Equation implies that if σ > 0 the
electric field at any point P is along outward
perpendicular n drawn to the plane and
if σ < 0, the electric field points inward
perpendicularly to the plane (-n ).
For a finite charged plane sheet, equation
is approximately true only in the
middle region of the plane and at points far
away from both ends.


(iii) Electric field due to two parallel
charged infinite sheets
Consider two infinitely large charged
plane sheets with equal and opposite charg e

densities +σ and -σ which are placed parallel
to each other as shown in the .
The electric field between the plates and
outside the plates is found using Gauss law.
The magnitude of the electric field due to
an infinite charged plane sheet is σ
2e
and it
points perpendicularly outward if σ > 0 and
points inward if σ < 0.
At the points P2
and P3
, the electric field
due to both plates are equal in magnitude
and opposite in direction . As
a result, electric field at a point outside the
plates is zero. But between the plates, electric
fields are in the same direction i.e., towards
the right and the total electric field at a point
P1
isThe direction of the electric field between
the plates is directed from positively charged
plate to negatively charged plate and is
uniform everywhere between the plates.


(iv) Electric field due to a uniformly
charged spherical shell
Consider a uniformly charged spherical
shell of radius R carrying total charge Q as
shown in Figure 1.40. The electric field at
points outside and inside the sphere can be
found using Gauss law.
Case (a) At a point outside the shell (r > R)
Let us choose a point P outside the shell
at a distance r from the centre as shown in
(a). The charge is uniformly
distributed on the surface of the sphere
(spherical symmetry). Hence the electric
field must point radially outward if Q > 0 and
point radially inward if Q < 0. So a spherical
Gaussian surface of radius r is chosen and

total charge enclosed by this Gaussian
surface is Q. Applying Gauss law

The electric field 
E and d A
point in
the same direction (outward normal) at
all the points on the Gaussian surface. The
magnitude of 
E is also the same at all points
due to the spherical symmetry of the charge
distribution

Case (b): At a point on the surface of the
spherical shell (r = R)
The electrical field at points on the
spherical shell (r = R) is given b

Electric field versus distance
for a spherical shell of radius R

Since Gaussian surface encloses no
charge, Q = 0

The electric field due to the uniformly
charged spherical shell is zero at all points
inside the shell.
A graph is plotted between the electric
field and radial distance

Gauss law is a powerful
technique whenever a given
charge configuration possesses
spherical, cylindrical or planar symmetry,
then the electric field due to such a charge
configuration can be easily found. If there
is no such symmetry, the direct method
(Coulomb’s law and calculus) can be used.
For example, it is difficult to use Gauss law to
find the electric field for a dipole since it has
no spherical, cylindrical or planar symmetry.

Atomic theories


Pencil (1 × 10-2 m)
Virus (1 × 10-6 m)
Red Blood Cell (1 × 10-4 m)
Dust Particle (1 × 10-7 m)
Now you could imagine how small an
atom would be.

An atom is thousand times smaller than
the thickest human hair. It has an average
diameter of 0.000000001 m or 1 × 10-9 m. To
understand the size of an atom, now let us find
what is the size of known things like pencil, red
blood cell, virus and dust particle.


Many scientists have studied the structure
of the atom and advanced their theories about
it. The theories proposed by Dalton, Thomson
and Rutherford are given below.

Stages of discoveries of constituents of atom.

Dalton’s atomic theory :
John Dalton
proposed an atomic
theory in the year
1808. He proposed that
matter consists of very
small particles which
he named atoms. An
atom is the smallest indivisible particle. It
is spherical in shape. His theory does not
propose anything about the positive and
negative charges of an atom. Hence, it was
not able to explain many of the properties of
substances.
Nanometer is the smallest
unit used to measure small
lengths. One nanometer
is equal to 1 × 10-9 m.


Thomson’s theory :
In 1897 J.J Thomoson
proposed a different
theory. He compared an
atom to a watermelon.
His theory proposed that
an atom has positively
charged part like the red
part of the watermelon and in it are embedded,
like the seeds, negatively charged particles
John Dalton
J.J. Thomsonwhich he called electrons. According to this
theory as the positive and negative charges
are equal, the atom as a whole does not have
any resultant charge.
Thomson’s greatest contribution was
to prove the existence of the negatively
charged particles or electrons in an atom by
experimentation. For this discovery, he was
awarded the Nobel Prize in 1906. Although
this theory explained why an atom is neutral,
it was an incomplete theory in other ways

Rutherford’s theory
There were
shortcoming in
Thomson’s theory.
Earnest Rutherford
gave a better
understanding. Earnest
Rutherford conducted
an experiment. He
bombarded a very thin layer of gold with
positively charged alpha rays. He found that most
of these rays which travel at a great velocity passed
through thin gold sheet without encountering any
obstacles. A few are, however, turned back fromthe sheet. Rutherford considered this remarkable
and miraculous as if a bullet had turned back
after colliding with tissue paper. Based on this
experiment, Rutherford proposed his famous
theory. They are:
1. The fact that most alpha particles pass
through the gold sheet means that the atom
consists mainly of empty space.
2. The part from which the positively charged
particles turned back is positively charged
but it is very small in size as compared to
the empty space.
From these inferences, Rutherford
presented his theory of the structure of atoms.
For this theory, he was awarded the Nobel prize
for chemistry.
Rutherford’s theory proposes the following.
1. The nucleus at the centre of the atom has
positive charge. Most of the mass of the
atom is concentrated in the nucleus.
2. The negatively charged electrons revolve
around the nucleus in specific orbits.
3. In comparison with the size of the atom, the
nucleus is very very small.

Scales of temperature

Celcius scale

Fahrenheit scale

Kelvin scale

There are 3 types of temperature scale

Celcius scale =100 degree celcius

Fahrenheit scale=32°F for water and 212°F for boiling point

Kelvin scale = 273K

SI unit of temperature is Kelvin

Scales of thermometers
Celsius scale
Celsius is the common unit of measuring
temperature, termed after Swedish astronomer,
Anders Celsius in 1742, before that it was
known as Centigrade as thermometers using
this scale are calibrated from (Freezing point
of water) 0°C to 100°C (boiling point of water).
In Greek, ‘Centium’ means 100 and ‘Gradus’
means steps, both words make it centigrade and
later Celsius.


Fahrenheit Scale
Fahrenheit is a Common unit to measure
human body temperature. It is termed after the
name of a German Physicist Daniel Gabriel
Fahrenheit. Freezing point of water is taken as
32°F and boiling point 212°F. Thermometers with
Fahrenheit scale are calibrated from 32°F to 212°F.


Kelvin scale
Kelvin scale is termed after Lord Kelvin.
It is the SI unit of measuring temperature and
written as K also known as absolute scale as it
starts from absolute zero temperature.

Unit of temperature.

Temperature Units:
There are three units which are used to
measure the temperature: Degree Celsius,
Fahrenheit and Kelvin.


Degree Celsius: Celsius is written as°C and read
as degree. For example 20°C; it is read as twenty
degree Celsius.

Celsius is called as Centigrade as
well.
Fahrenheit: Fahrenheit is written as °F for
example 25°F; it is read as twenty five degree
Fahrenheit.


Kelvin: Kelvin is written as K. For example
100K; it is read as hundred Kelvin.
 The SI unit of temperature is kelvin (K)

What is light year?

        Light year
        The nearest star to our
        solar system is Proxima
        Centauri.
        It is at a distance of
        2,68,770 AU. We can note here
        that using AU for measuring
        distances of stars would be unwieldy.
        Therefore,
        astronomers use a special unit, called ‘light
        year’, for measuring the distance in deep space.
        We have learnt that the speed of light in vacuum
        is 3 × 108
        m/s.
        This means that light travels a
        distance of 3 × 108
        m in one second. In a year
        (non-leap), there are 365 days. Each 24 hours, each hour has 60 minutes and each
        minute has 60 seconds.
        Thus, the total number of seconds in one year
        = 365 × 24 × 60 × 60
        = 3.153 × 107
        second
        If light travels at a distance of 3 × 108
        m in
        one second, then the distance travelled by light
        in one year = 3 × 108
        × 3.153 × 107
        = 9.46 × 1015
        m. This distance is known as one light year.
        One light year is defined as the distance
        travelled by light in vacuum during the period of
        one year.
        1 Light year = 9.46 × 1015 m.
        In terms of light year, Proxima Centauri
        is at 4.22 light-years from Earth and the Solar
        System. The Earth is located about 25,000 light�years away from the galactic centre. 

        Nothing is impossible for willing heart

        Breakfast at my House

        During the week we’re often walking out the door with a coffee in one hand and slice of toast in the other, but on weekends breakfast is never rushed. It’s a late affair, sometimes spilling over to lunch, with lots of reading and chatter in between courses of fruits, poached eggs, honey and toast. One of our favorite things we like to serve when friends are visiting are buckwheat blueberry pancakes.

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