Herbaria

Herbaria :Herbaria is a place where dried and pressed plants specimens, mounted on sheets are kept systematically according to a widely accepted system of classification. Herbarium is a repository or store house for future use.

• It provide information about the local flora as well as flora of distant area.
• It provides information about the ecology of different places. The information is useful in locating wild varieties and relatives of economically important plants.
• It serves as a quick referal system for taxonomic studies.
• Largest herbarium of the world is at kew.

                               

                                                                                   https://youtu.be/UCHIvvAvekA

Cyanobacteria

Cyanobacteria :Cyanobacteria or blue-green algae are gram(+ve) photosynthetic prokaryotes known to be the earliest colonisers of barren area because of their ability to perform oxygenic photosynthesis. Cyanobacteria contains chlorophyll a, carotenoids and phycobilins as photosynthetic pigments.

Food is stored in the form of cyanophycean starch, lipid globules and protein granules. 

They have evolved more than 3 billion years back, added oxygen to the atmosphere and paved the path for evolution of aerobic forms, including aerobic bacteria.

                                                                             https://youtu.be/UCHIvvAvekA

Diatomite

Diatomaceous earth :Silica shell of dead diatoms are nearly indestructible and thus, get accumulated at the sea bed. Such huge rock like deposits of hard shell of diatoms constitutes earth, which is mined to obtain a whitish powder called diatomites or Kieselguhr.

Diatomites are rough and gritty. Because of these features, it is used in filters in brewing industry, sugarcane refineries, in metal polishing, toothpaste, for making insulating bricks, water glass or sodium silicates and strong acids.

This is added to paints to increase their night visibility. The common example of diatoms are Triceratium, Pleurosigma, Navicula, Cymbella.

                                                                               https://youtu.be/UCHIvvAvekA

Thermodynamics equilibrium

Thermodynamics equilibrium : A system in which the state variables have constant values throughout the system is said to be in state of thermodynamics equilibrium.

The criteria for equilibrium :

1) The temperature of the system must be uniform and must be same as the temperature of the surrounding (thermal equilibrium).

2) The mechanical properties of the system must be uniform throughout the system (mechanical equilibrium). That is no mechanical work is done by one part of the system on any other part of the system.

3) The chemical composition of the system must be uniform with no net chemical changes (chemical equilibrium).

                                                                                                     https://youtu.be/UCHIvvAvekA

Negative temperature

Negative temperature : A part from the system i.e., the nucleus of a solid can have a negative temperature. This sub-system is considered isolated from the main system.

The specific heat of the subsystem tends to zero at high temperature. A small amount of heat energy tends to raise the temperature of the sub-system to infinitely. It is possible to add still more energy to the sub-system at infinity and force the sub-system into the negative temperature region.

          The negative temperature are hotter than the positive temperature. (-0) is the hottest temperature and (+0) is the coldest temperature.

                                                                          https://youtu.be/UCHIvvAvekA

second law of thermodynamics

Second law of thermodynamics :  The law specifying the condition of transformation of heat into work is called the Second law of thermodynamics.

There are several statements which explains the second law of thermodynamics ------

1) Kelvin-Planck's statement : It is impossible to construct an engine, operating in a cycle, to extract heat from hot body and convert it completely into mechanical work done i.e., 100% conversion of heat into work is impossible.

2) Clausius statement : It is impossible for any cyclic machine to produce no any effect other than to convey heat continuously from one body to another at a higher temperature.

3) Kelvin's statement : It is impossible to get continuously supply of work by cooling a body to a temperature lower than that of the coldest of its surroundings.

                                                  

                                                                                                              https://youtu.be/UCHIvvAvekA 

Third law of thermodynamics

Third law of thermodynamics :- There are several statements for third law of thermodynamics:

1) Nernst statement : The heat capacity of a solid tends to zero, as the absolute zero of temperature approached and the internal energies and entropy of all the substances becomes equal there, approaching common value asymptotically.

2) Planck's statement :  The entropy of every actual substance in the pure state is zero at the absolute zero temperature.

3) Fowler and Gauggenheim's statement : It is impossible by any procedure, to reduce a system to absolute zero temperature in a finite number of operation.

                                                                   https://youtu.be/UCHIvvAvekA

Kinetic Theory of gases

 Kinetic Theory of Gases :-

• Gases consist of large number of molecules.
• Molecules of gases are always in random motion.
• The volume of a gas molecule is negligible as compared to the total volume occupied by the gas.
• During random motion molecules of gas collides with each other and with the walls of the container.
• The collision of the gas molecules are perfectly elastic. There is no loss in kinetic energy and the total momentum remains conserved.
• The momentum transfer by the molecules of the gas during collision on the surface of the container is called as PRESSURE exerted by the gas.
• Intermolecular  forces are negligible except during the collision of molecules.
• A molecule moves with uniform velocity during collisions{ignoring gravity}.

                                                                                                                 https://youtu.be/O3D2belxKBs

torsional pendulum

 Torsional Pendulum:

 In torsional pendulum, an extended body is suspended by a light thread or wire. The body is rotated through an angle about the axis of rotation.

The wire remains vertical during this motion but twist Ө  is produced in the wire. The twisted wire exerts a restoring torque on the body, which is directly proportional to the angle of twist 

                                 τ α –θ

                                 τ = -k θ   

where k is the proportionality constant called torsional constant of the wire.

If I be the moment of inertia of the body about the vertical axis, then the angular acceleration of the body will be -------

     As we know,            τ = I α

                                     α = τ/I
                                     α = –kθ/I
                                     α = –ω2θ
Therefore,                    ω2 = k/I

                                             ω = (k/I)^1/2    

     As we know,                   T = 2π/ω   

                                             T = 2π(I/k)^1/2     

                                                                      https://youtu.be/O3D2belxKBs

Torricelli's theorem

 Consider a vessel which is filled with water, at the surface of water P1 pressure is applied and the velocity of water is zero (V1 = 0). Let a hole is made at a point b from which water is coming out with velocity V & at that point the pressure is P2 .

 Let ‘H’ is the height from surface to the bottom of the vessel & ‘h’ is the height from the surface to the hole. Then the remaining height is

(H – h).  

 According to Pascal's law -

     P1 = P2 = P

     V1 = 0

According to Bernoulli's theorem-

P1 + ½ ρv12 + ρgh1 = P2 + ½ ρv22 + ρgh2

P + ½ ρv12 + ρgH = P+ ½ ρv22 + ρg(H – h)

½ ρ(0)2 + ρgH =  ½ ρv2 + ρg(H – h)

       ρgH =  ½ ρv2 + ρgH - ρgh

       ½ ρv2 = ρgh

       v2 = 2gh

        v = √2gh

Hence the speed of e-flux is  v = √2gh.

 Note: a) velocity of e-flux is independent on the nature of liquid, quantity of liquid in the vessel and area of orffice.

b) Path of liquid will be parabola.

c) Greater is the distance of the hole from the free surface greater will be the velocity.

  

                                                                                     https://youtu.be/O3D2belxKBs

Density

Density (ρ) of any substance can be defined as the mass per unit volume or

                      density = mass / volume

                               ρ = m / v

Relative density

 The ratio of density of substance to the density of water at 4°C is called relative density or specific gravity.

    Relative density = density of substance / density of water at 4°C .

 

Note :  Relative density is a pure ratio. So, it has no units. 

            Density of water at 4°C in CGS is 1 g/cm3 . Therefore, numerically the relative density  and density of substance (in CGS) are equal. 

exam: Relative density of an oil is 0.6. find the absolute density in CGS and SI unit.

sol:  Density of oil (in CGS) = relative density (g/cm3) 

                     absolute density = 0.6 g/cm3

                        absolute density = 600 kg/m3

                                                         https://youtu.be/UCHIvvAvekA

Venturimeter

It is a device based on the horizontal extension of the Bernoulli’s theorem. It is a device used to measure the rate of flow of liquid through the pipe.

According to Bernoulli’s theorem –

P1 + ½ ρv12 + ρgh1 = P2 + ½ ρv22 + ρgh2

 P1 + ½ ρv12 + ρgh =  P2 + ½ ρv22 + ρgh

since h1 = h2 , so

P1 – P2 = ½ ρ ( v22 – v12 )

Divide and multiply by v12 -----

∆P = ½ ρv12 ( v22 – v12 ) / v12

∆P = ½ ρv12 (v22 /v12  - 1)

          According to equation of continuity-----

          A1 v1 = A2 v2 ,   v2 /v1 = A1 /A2

          ∆P = ½ ρv12 { (A1 /A2 )2 – 1 }

          ∆P = ½ ρv12 (A12 – A22 ) /A22

          hρHg g = ½ ρv12 (A12 – A22 ) /A22    {ρHg  = density of mercury}

          v12 = 2 hρHggA22 / ρ(A12 – A22)

                         v1 = A2 {2 hρHgg / ρ(A12 – A22)}1/2

                                           https://youtu.be/UCHIvvAvekA

Atmospheric pressure 

The pressure exerted by the earth's atmosphere is called atmospheric pressure. Atmospheric pressure changes with weather and elevation. 

Normal atmospheric pressure at sea level (an average value) is 1.013 x 105 Pa.

                        1 atm = 1.013 x 105 Pa.

Absolute pressure and Gauge pressure

The excess pressure above atmospheric pressure is usually called gauge pressure and the total pressure is called absolute pressure.

Thus,

         Gauge pressure = absolute pressure - atmospheric pressure.

                                         

                                                https://youtu.be/UCHIvvAvekA

Capillary Tube

If a tube of very narrow bore (capillary tube) is dipped in a liquid, it is formed that the liquid in the tube either ascent or descents relative to the surrounding  liquid. This phenomenon is called capillarity.

The main cause of capillarity is the difference in pressure on two sides concave or convex surface of liquid.

Consider a capillary tube of radius 'r' dipped in a liquid of surface tension 'T' and density ρ.

    cosӨ = r/R    {R=radius of meniscus}

    R = r/ cosӨ   

    

   As we know, P = 2T/R

          hρg = 2T/R    {as P=hρg}

          h = 2T / ρgR

          h = 2TcosӨ / ρgR

 So the height ascent or descent in the capillary tube will be  ----

                    h = 2TcosӨ / ρgR

                                                      https://youtu.be/xNREviwPrOg

                

 

Barometer

It is a device used to measure atmospheric pressure. In principle, any liquid can be used to fill the barometer, but mercury is the liquid generally filled because its great density makes possible any instrument of reasonable size.

         

         P₁ = P₂

          P₂ = atmospheric pressure (P₀)

         P₁ = 0 + ρgh   { ρ= density of mercury}

         P₀ = ρgh

Thus mercury barometer reads the atmospheric pressure (P₀)  directly from the height of the mercury column.

For example, if the height of mercury in the barometer is 760 mm, then the atmospheric pressure will be ----

As,     P₀ = ρgh

        P₀ = (13.6 x 10³)(9.8)(0.760)

         P₀ = 1.013 x 10⁵ N/m²

                                                                 https://youtu.be/O3D2belxKBs

Law of Floatation

Consider an object of volume V and density ρs floating in a liquid of density ρl. Let Vi be the volume of object immersed in the liquid. For equilibrium of object--

                 Weight = Upthrust

                 Vρs g = Viρl g

                 Vi / V = ρs / ρl

 This is the fraction of volume immersed in liquid.

Percentage of volume immersed in liquid----------------

  (Vi/V)100 = (ρs / ρl)100

Three possibilities are now arise----

a) If ρs < ρl, only fraction of object will be immersed in the liquid. This fraction can be calculated by the above equation.

b) If ρs = ρl, the whole of the rigid body will be immersed in the liquid. Hence , the body remains floating in the liquid wherever it is left.

c) If ρs > ρl, the body will sink.

                                                        https://youtu.be/O3D2belxKBs