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  • Question: What is the unit of molar conductivity?

    Posted in: Chemistry | Date: 12/09/2015

    Answer:

    the unit of molar conductivity is: siemens metre square per mole or siemens per metre per molarity

  • Answer:

    Stable equilibrium

    When the center of gravity of a body lies below point of suspension or support, the body is said to be in STABLE EQUILIBRIUM. For example a book lying on a table is in stable equilibrium.

    Explanation

    A book lying on a horizontal surface is an example of stable equilibrium. If the book is lifted from one edge and then allowed to fall, it will come back to its original position.  Other examples of stable equilibrium are bodies lying on the floor such as chair, table etc.

    Reason of stability

    When the book is lifted its center of gravity is raised . The line of action of weight passes through the    base of the book. A torque due to weight of the book brings it back to the original position.

  • Question: What do you mean by noble metals?

    Posted in: Chemistry | Date: 12/09/2015

    Answer:

     the noble metals are metals that are resistant to corrosion and oxidation in moist air (unlike most base metals). The short list of chemically noble metals (those elements upon which almost all chemists agree) comprises ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold.In chemistry, the noble metals are metals that are resistant to corrosion and oxidation in moist air (unlike most base metals). The short list of chemically noble metals (those elements upon which almost all chemists agree) comprises ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold.In chemistry, the noble metals are metals that are resistant to corrosion and oxidation in moist air (unlike most base metals). The short list of chemically noble metals (those elements upon which almost all chemists agree) comprises ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold.

  • Question: Why Sulphur in vapour state exhibits paramagnetism?

    Posted in: Chemistry | Date: 12/09/2015

    Answer:

    in vapour state sulphur exists as  S2 molecules and has 2 unpaired electrons in antibonding pi orbital and hence exhibits paramagnetism

  • Question: What is current density and conductance ?

    Posted in: Physics | Date: 12/09/2015

    Answer:

    Current Density, Conductance And Electrical Conductivity

    Current density at a point in a conductor is defined as the amount of current flowing per unit area of the conductor around that point provided the area is held in a direction normal to the current.

    Let I be the current distributed uniformly across a conductor of cross-sectional area A. The magnitude of the current density for all points on that cross-section of the conductor is

    J=I/A

    Current density is a vector quantity. Its direction is the direction of motion of positive charge.

    As      I=Anevd (refer article of relation between current and drift velocity)

    Therefore                                     J=I/A=Anevd/A

    Or                                                 J=nevd

    The unit of current density is:

    Ampere(metre)-2 or Am-2

    For a particular surface of conductor, the current is the flux of J over the surface S and is given by

    I=∫ J.ds

    Where ds is elementary surface area vctor of an element taken over the particular surface S and integral is taken over the surface in question.

    Conductance(G). The inverse of resistance (R) is called conductance of a conductor, that is,

    Conductance, G=1/R

    The unit of conductance is mho or siemen(symbol S). Its unit is inverse of Resistance that we have discussed in Ohm’s law.

    Electrical conductivity. The inverse of resistivity (ρ) of a conductor is called its electrical conductivity(σ) i.e.

    σ =1/ ρ

    the unit of electrical conductivity is mho m-1 or siemens/m.

  • Question: What is Ferrimagnetism?

    Posted in: Chemistry | Date: 12/09/2015

    Answer:

    In physics, a ferrimagnetic material is one that has populations of atoms with opposing magnetic moments, as in antiferromagnetism; however, in ferrimagnetic materials, the opposing moments are unequal and a spontaneous magnetization remains.[1] This happens when the populations consist of different materials or ions (such as Fe2+ and Fe3+).

    Ferrimagnetism is exhibited by ferrites and magnetic garnets. The oldest known magnetic substance, magnetite (iron(II,III) oxide; Fe3O4), is a ferrimagnet; it was originally classified as a ferromagnet before Néel's discovery of ferrimagnetism and antiferromagnetism in 1948.[2]

    Some ferrimagnetic materials are YIG (yttrium iron garnet), cubic ferrites composed of iron oxides and other elements such as aluminum,cobalt, nickel, manganese and zinc, hexagonal ferrites such as PbFe12O19 and BaFe12O19, and pyrrhotite, Fe1-xS.[3]

  • Answer:

    Potassium permanganate is produced industrially from manganese dioxide, which also occurs as the mineral pyrolusite. The MnO2 is fused with potassium hydroxide and heated in air or with another source of oxygen, like potassium nitrate or potassium chlorate.[3]This process gives potassium manganate:

    2 MnO2 + 4 KOH + O2 → 2 K2MnO4 + 2 H2O

    (Using sodium hydroxide the end product is not sodium manganate but an Mn(V) compound which is one reason the potassium permanganate is more commonly used than sodium permanganate. Furthermore the potassium salt crystallizes better

    The potassium manganate is then converted into permanganate by electrolytic oxidation in alkaline media:

    K2MnO4 + H2O → KMnO4 + KOH + 1/2 H2

  • Answer:

    The characteristics of an image produced by a pinhole camera  The image produced by a pinhole camera is usually smaller than the object and appears to be inverted on both the vertical and horizontal axis when compared to the actual object. The image itself can be called "real" because it is visible on the screen.  Characteristics of the image:   

    • generally smaller than the object 
    • vertical inversion (upside-down) 
    • horizontal inversion (symmetric) 
    • real

    The behaviour of light 

     

    The rays coming from the object which pass through the pinhole must converge in order to cross at the level of the hole. Then, once inside the pinhole, the rays diverge. The vertical and horizontal inversions of the image when compared to the object can thus be explained by simple geometric logic. The analysis of the image produced by a pinhole camera demonstrates the rectilinear propagation of light. 

  • Answer:

    Laterel shift is directly proportional to the thickness of the slab. The relation is ,

    d={t/cos r}xsin (i-r)

    where d=lateral displacement

    t=thickness of the slab

    i=angle of incidence

    r=angle of refraction

  • Question: What is azimuthal quantum ? What is it's significance?

    Posted in: Chemistry | Date: 06/11/2015

    Answer:

    The azimuthal quantum number is a quantum number for an atomic orbital that determines its orbital angular momentum and describes the shape of the orbital. The azimuthal quantum number is the second of a set of quantum numbers which describe the unique quantum state of an electron (the others being the principal quantum number, following spectroscopic notation, the magnetic quantum number, and the spin quantum number). It is also known as the orbital angular momentum quantum number, orbital quantum number or second quantum number, and is symbolized as â„“.

  • Question: What is meant by delocalisation?

    Posted in: Chemistry | Date: 06/11/2015

    Answer:

    Delocalised electrons are spread across more than one atom. Usually electrons in materials are bound to one atom, and atoms are held together by the interactions of the charges on different atoms. In some cases, electrons can be shared between atoms, and are then called delocalised. In the case of hydrocarbons, delocalisation occurs in Benzene rings, where a hexagon of six carbon atoms has delocalised electrons spread over the whole ring. In metals, electrons are delocalised over the whole crystal structure, and carry currents - the outer electrons of the metal atoms are shared in an electron sea, and are not confined to particular atoms.  To really visualize this you have to think of an electron as a probability cloud, and just see that cloud spread over more than one atom; then it's not such a leap to see a delocalised cloud spread all through a metal. The planetary orbit picture of electrons isn't much use for delocalisation; forget about orbits, and think of clouds instead!

  • Answer:

    A musical pitch is a blend of many different frequencies beside the fundamental. Here's a visualization of the different vibrational modes of an ideal string. The string's movements are the sum of all these different modes simultaneously.The top row shows the fundamental frequency, the one you hear as the pitch -- say it's a violin string playing A 440. The second row shows the first harmonic, the string vibrating in halves, producing A 880. The harmonic is quieter than the fundamental, so you aren't necessarily conscious of it, but you can isolate it by lightly touching the string at its halfway point while playing. The other rows show other harmonics, vibrations of the string in integer ratios, each producing a pitch that's an integer multiple of the fundamental frequency. The second harmonic is E 1320; the third is A 1760; the fourth is C# 2200. In an ideal string, the harmonics would continue to get infinitely higher, beyond the range of your hearing. As the harmonics get higher, they also get quieter and subtler. Still, they all have an impact on the overall sound of the instrument. All musical instruments have overtones: winds, the human throat, speaker cones, even well-tuned drumheads. Real instruments aren't ideal, so they don't produce all of the overtones pictured above equally. Different instruments will produce different overtones more or less prominently, and will mix in some non-harmonic overtones and noise. Also, real notes begin with a short burst of noise, and decay in characteristic ways. The precise blend of harmonic and inharmonic frequencies and noise in a note over time determines the timbre of the instrument. Read more about how harmonics form the basis of western music th

  • Answer:

    In 1820 Hans Christian Oersted during his experiment found that when an electric current flows in a wire it moves a compass needle and this effect lasts as long as the current flows through the wire. This experiment established the relation between electricity and magnetism.

    If we place a compass near to a electric current carrying wire we can observe a deflection in compass needle. The needle of compass gets deflected by a magnetic field produced by current carrying wire. This effect which produced by the flow of electric current is called “Magnetic Effect” of electric current.

     

  • Question: What is the definition of Bond Dissociation Enthalpy.

    Posted in: Chemistry | Date: 10/11/2015

    Answer:

    The bond dissociation enthalpy is the energy needed to break one mole of the bond to give separated atoms - everything being in the gas state.

  • Question: Define emperical formula

    Posted in: Chemistry | Date: 10/11/2015

    Answer:

    The empirical formula of a compoundis a formula that shows the ratio of elements present in the compound. The ratios are denoted by subscripts next to the element symbols

  • Answer:

    Shortwave frequencies are capable of reaching any location on the Earth because they can be reflected by the ionosphere (a phenomenon known as Skywave propagation). 

  • Question: What are polyesters?

    Posted in: Chemistry | Date: 30/11/2015

    Answer:

    P

    olyester is a term often defined as “long-chain polymers chemically composed of at least 85% by weight of an ester and a dihydric alcohol and a terephthalic acid”. In other words, it means the linking of several esters within the fibers. Reaction of alcohol with carboxylic acid results in the formation of esters.

    Polyester also refers to the various polymers in which the backbones are formed by the “esterification condensation of polyfunctional alcohols and acids”.

    Polyester can also be classified as saturated and unsaturated polyesters.

    Saturated polyesters refer to that family of polyesters in which the polyester backbones are saturated. They are thus not as reactive as unsaturated polyesters. They consist of low molecular weight liquids used as plasticizers and as reactants in forming urethane polymers, and linear, high molecular weight thermoplastics such as polyethylene terephthalate (Dacron and Mylar). Usual reactants for the saturated polyesters are a glycol and an acid or anhydride.

    Unsaturated polyesters refer to that family of polyesters in which the backbone consists of alkyl thermosetting resins characterized by vinyl unsaturation. They are mostly used in reinforced plastics. These are the most widely used and economical family of resins.

  • Question: Describe what happens when boric acid is heated.

    Posted in: Chemistry | Date: 30/11/2015

    Answer:

    Boric acid is soluble in boiling water. When heated above 170 °C, it dehydrates, forming metaboric acid (HBO2):

    H3BO3 → HBO2 + H2O

    Metaboric acid is a white, cubic crystalline solid and is only slightly soluble in water. Metaboric acid melts at about 236 °C, and when heated above about 300 °C further dehydrates, forming tetraboric acid or pyroboric acid (H2B4O7):

    4 HBO2 → H2B4O7 + H2O

    The term boric acid may sometimes refer to any of these compounds. Further heating leads to boron trioxide.

    H2B4O7 → 2 B2O3 + H2O

    There are conflicting interpretations for the origin of the acidity of aqueous boric acid solutions. Raman spectroscopy of strongly alkaline solutions has shown the presence of B(OH)− 4 ion,[3] leading some to conclude that the acidity is exclusively due to the abstraction of OH− from water:[3][4][5][6]

    B(OH)3 + H2O  B(OH)− 4 + H+ (K = 7.3x10−10; pK = 9.14)

    or more properly expressed in the aqueous solution:

    B(OH)3 + 2 H2O  B(OH)− 4 + H3O+

    This may be characterized[4][5][6] as Lewis acidity of boron toward OH−, rather than as Brønsted acidity.

    However other sources[7] say that boric acid is also a tribasic Brønsted acid, with successive ionization steps:

    B(OH)3  BO(OH)− 2 + H+ (Ka1 = 5.8x10−10; pKa1 = 9.24)

    BO(OH)− 2  BO2(OH)2− + H+ (Ka2 = 4x10−13; pKa2 = 12.4)

    BO2(OH)2−  BO3− 3 + H+ (Ka3 = 4x10−14; pKa3 = 13.3)

    Since the value of Ka1 is comparable to that of the reaction with OH−, the concentrations of BO(OH)− 2 and B(OH)− 4 are similar.[7]

    Polyborate anions are formed at pH 7–10 if the boron concentration is higher than about 0.025 mol/L. The best known of these is the 'tetraborate' ion, found in the mineral borax:

    4[B(OH)4]− + 2H+  [B4O5(OH)4]2− + 7H2O

    Boric acid makes an important contribution to the absorption of low frequency sound in seawater.

  • Answer:

    Blast Furnace

    The blast furnace is a cylindrical tower like structure about 25m to 35m high. It has an outer shell of steel. Inside of furnace is lined with fire bricks. The top of the furnace is closed by a cup-cone feeder.  

    The charge

     

    The charge consists of : roasted ore Coke Limestone

     

    Details of reduction

    The charge is fed into the furnace from its top. A preheated blast of air at 1500OC, is blown into the furnace under pressure near to the bottom. The blast oxidizes carbon to CO2.

    C + O2  CO2 + heat

    Formation of CO2 is an exothermic reaction in which a huge amount of heat is liberated which rises the temperature to 1900OC in this region. As the CO2 passes upwards, it reacts more coke to form carbon monoxide.

    CO2 + C  2CO + heat

    Formation of CO is an endothermic reaction and the temperature in this region falls to 1100OC. CO is the main reducing agent in the upper portion of blast furnace.Reactions in blast furnace  

    Fe2O3 + 3C  2Fe + 3CO Fe3O4 + 4CO  3Fe + 4CO2  CO2 + C  2CO     

    Overall reaction

     

    Fe2O3 + 3CO  2Fe + 3CO2

    The liquid iron runs downward to the bottom of the furnace and is withdrawn through tap hole.

    Slag formation

    Lime stone on heating decomposes to CaO and CO2.

    CaCO3  CaO + CO2

    CaO now reacts the impurities of ore called GANGUE to form slag. Slag is the mixture of CaSiO3  and Ca(AlO2)2. The slag floats over the top of molten iron. Slag is a useful byproduct. It is used in road making, cement manufacturing a light weight building materials.

    Flux + Gangue  Slag            CaO + SiO2  CaSiO3     CaO + Al2O3  Ca(AlO2)2

  • Answer:

    A bimetallic strip is simply two strips made from different metals or metal alloys joined together.  The magic of bimetallic strips is that, being made of two metals, they conduct heat to different degrees.  Different metals and metal alloys (such as brass and steel) have different coefficients of expansion.  That is, they will expand by different amounts.

    Therefore, if you apply heat to a bimetallic strip, one metal will expand more than the other and the strip will curve.  You can design an electrical circuit so that, when the strip curves a certain distance, the circuit then becomes complete.  If you include a bell in this circuit, it will ring when enough heat has caused the strip to curve.

    All you need now is to design a circuit with an electrical power supply (mains or batteries), a bell, a bimetallic strip and the connecting wires!

    To find out more about the metals used in bimetallic strips and their alternative use as circuit breakers, click on the link below.

  • Question: How is water cooled in a soil pitcher? please tell

    Posted in: Physics | Date: 30/11/2015

    Answer:

    Have you ever had a drink of cool refreshing water from a ‘matka‘ or earthen clay pot placed outside? Surprisingly enough, the pots are exposed to blazing sunlight, yet the water within stays so cool. How is that possible?

    This is because of a physical process known as evaporation. When a liquid changes to a gaseous (or vapour) state without boiling, it is known as evaporation.

    A matka is made of mud and has many minute pores (extremely small holes). No matter how tightly you pack the mud, these pores remain. It is through these pores that the water, placed inside the matka, oozes out. Now, to evaporate, the water needs to absorb heat, which will change it to vapour.

    The only way the water oozing out of the matka can turn to vapour is by absorbing heat from the liquid within the matka and the matka itself. Due to this process of continuous absorption of heat from the water inside the matka, in a few hours, this water becomes cool.

  • Answer:

    RELATIONSHIP BETWEEN CONSERVATIVE FORCES AND POTENTIAL ENERGY

    Once again let us consider a particle that is part of a system. Suppose that the particle moves along the x axis, and assume that a conservative force with an x component Fx acts on the particle. Earlier in this chapter, we showed how to determine the change in potential energy of a system when we are given the conservative force. We now show how to find Fx if the potential energy of the system is known.  We know that the work done by the conservative force as its point of application undergoes a displacement Δx equals the negative of the change in the potential energy associated with that force; that is, W = FxΔx = -ΔU. If the point of application of the force undergoes an infinitesimal displacement dx, we can express the infinitesimal change in the potential energy of the system dU as Therefore, the conservative force is related to the potential energy function through the relationship 3  That is, any conservative force acting on an object within a system equals the negative derivative of the potential energy of the system with respect to x.  We can easily check this relationship for the two examples already discussed. In the case of the deformed spring, Us = ½ Kx2, and therefore which corresponds to the restoring force in the spring. Because the gravitational potential energy function is Ug = mgy, it follows from Equation 8.16 that Fg = -mg when we differentiate Ug with respect to y instead of x.  We now see that U is an important function because a conservative force can be derived from it. Furthermore, Equation 8.16 should clarify the fact that adding a constant to the potential energy is unimportant because the derivative of a constant is zero.

  • Question: Describe the process of sky wave propagation.

    Posted in: Physics | Date: 30/11/2015

    Answer:

    Sky Wave

    The sky wave, often called the ionospheric wave, is radiated in an upward direction and returned to Earth at some distant location because of refraction from the ionosphere. This form of propagation is relatively unaffected by the Earth's surface and can propagate signals over great distances. Usually the high frequency (hf) band is used for sky wave propagation. The following in-depth study of the ionosphere and its effect on sky waves will help you to better understand the nature of sky wave propagation.

    STRUCTURE OF THE IONOSPHERE

    As we stated earlier, the ionosphere is the region of the atmosphere that extends from about 30 miles above the surface of the Earth to about 250 miles. It is appropriately named the ionosphere because it consists of several layers of electrically charged gas atoms called ions. The ions are formed by a process called ionization.

    Ionization

    Ionization occurs when high energy ultraviolet light waves from the sun enter the ionospheric region of the atmosphere, strike a gas atom, and literally knock an electron free from its parent atom. A normal atom is electrically neutral since it contains both a positive proton in its nucleus and a negative orbiting electron. When the negative electron is knocked free from the atom, the atom becomes positively charged (called a positive ion) and remains in space along with the free electron, which is negatively charged. This process of upsetting electrical neutrality is known as IONIZATION.

    The free negative electrons subsequently absorb part of the ultraviolet energy, which initially freed them from their atoms. As the ultraviolet light wave continues to produce positive ions and negative electrons, its intensity decreases because of the absorption of energy by the free electrons, and an ionized layer is formed. The rate at which ionization occurs depends on the density of atoms in the atmosphere and the intensity of the ultraviolet light wave, which varies with the activity of the sun.

    Since the atmosphere is bombarded by ultraviolet light waves of different frequencies, several ionized layers are formed at different altitudes. Lower frequency ultraviolet waves penetrate the atmosphere the least; therefore, they produce ionized layers at the higher altitudes. Conversely, ultraviolet waves of higher frequencies penetrate deeper and produce layers at the lower altitudes.

    An important factor in determining the density of ionized layers is the elevation angle of the sun, which changes frequently. For this reason, the height and thickness of the ionized layers vary, depending on the time of day and even the season of the year.

    Recombination

    Recall that the process of ionization involves ultraviolet light waves knocking electrons free from their atoms. A reverse process called RECOMBINATION occurs when the free electrons and positive ions collide with each other. Since these collisions are inevitable, the positive ions return to their original neutral atom state.

    The recombination process also depends on the time of day. Between the hours of early morning and late afternoon, the rate of ionization exceeds the rate of recombination. During this period, the ionized layers reach their greatest density and exert maximum influence on radio waves. During the late afternoon and early evening hours, however, the rate of recombination exceeds the rate of ionization, and the density of the ionized layers begins to decrease. Throughout the night, density continues to decrease, reaching a low point just before sunrise.

     

    Four Distinct Layers

    The ionosphere is composed of three layers designated D, E, and F, from lowest level to highest level as shown in figure 2-14. The F layer is further divided into two layers designated F1 (the lower layer) and F2 (the higher layer). The presence or absence of these layers in the ionosphere and their height above the Earth varies with the position of the sun. At high noon, radiation in the ionosphere directly above a given point is greatest. At night it is minimum. When the radiation is removed, many of the particles that were ionized recombine. The time interval between these conditions finds the position and number of the ionized layers within the ionosphere changing. Since the position of the sun varies daily, monthly, and yearly, with respect to a specified point on Earth, the exact position and number of layers present are extremely difficult to determine. However, the following general statements can be made:

    Figure 2-14. - Layers of the ionosphere.

     

    1. The D layer ranges from about 30 to 55 miles. Ionization in the D layer is low because it is the lowest region of the ionosphere. This layer has the ability to refract signals of low frequencies. High frequencies pass right through it and are attenuated. After sunset, the D layer disappears because of the rapid recombination of ions.

    2. The E layer limits are from about 55 to 90 miles. This layer is also known as the Kennelly-Heaviside layer, because these two men were the first to propose its existence. The rate of ionic recombination in this layer is rather rapid after sunset and the layer is almost gone by midnight. This layer has the ability to refract signals as high as 20 megahertz. For this reason, it is valuable for communications in ranges up to about 1500 miles.

    3. The F layer exists from about 90 to 240 miles. During the daylight hours, the F layer separates into two layers, the F1 and F2 layers. The ionization level in these layers is quite high and varies widely during the day. At noon, this portion of the atmosphere isclosest to the sun and the degree of ionization is maximum. Since the atmosphere is rarefied at these heights, recombination occurs slowly after sunset. Therefore, a fairly constant ionized layer is always present. The F layers are responsible for high-frequency, long distance transmission.

  • Question: Magnesium wire is burnt in presence of oxygen?

    Posted in: Physics | Date: 30/11/2015

    Answer:

    a) Magnesium Oxide  b) Activation energy is needed to start the reaction, once activation energy is satisfied, reaction will starts, bonds of oxygen molecules will break to combine with magnesium forming magnesium oxide.  (Note : When pure metals are burnt in AIR, remember that it will only react with oxygen forming metal oxides)  c) Yes you can get back the elements by electrolysis of molten magnesium oxide. *It must be in molten state, refer to metal reactivity chapter and electrolysis*  d) 2Mg (s) + O2 (g) ----> 2MgO (s) 

  • Question: Describe the structure of the common form of ice.

    Posted in: Chemistry | Date: 30/11/2015

    Answer:

    Ice has a hexagonal form if crystallized at atmospheric pressure. However when temperatures are low, ice condenses to cubic form. Here's the structure of ice: As you can see, the structure is highly ordered. Each oxygen atom is surrounded tetrahedrally by four other oxygen atoms at a distance of 276 pm. Because of the presence of large interstitial spaces, ice can hold a number of substances inside the lattice structure. It also has hydrogen bonding within the structure which is seen in the diagram below.  

  • Question: What is the origin of geometric isomerism in alkenes?

    Posted in: Chemistry | Date: 30/11/2015

    Answer:

    Cis- and trans- terminology If alkenes have two different substituents at each end of the C=C then they can exist as stereoisomers (as geometric isomers). This is because there is restricted rotation of the double bond due to the pi bond which means they don't readily interconvert. Examples:  

    • all terminal alkenes i.e. those with a C=CH2 unit can not exist as cis- and trans- isomers.
    • similarly, all 1,1-symmetrically disubstituted alkenes i.e. those with a C=CR2 unit can not exist as cis- and trans- isomers.
    • alkenes with the R1-CH=CH-R2 unit can exist as cis- and trans- isomers.

    If we consider the general alkene unit shown below, then the alkene can exist as cis and trans isomers only if R1 is not equal to R2 AND R3 is not equal to R4.   

     

    There are two ways to name these types of isomers, one is the cis / trans method which is described here, the other is E / Z method that is described on the next page.

    Misconception Alert!

    cis ¹ Z and trans ¹ E

    In general terms there is NO specific relationship between cis and trans / E and Z as they are based on fundamentally different naming rules.

    1,2-disubstituted alkenes are described as:

    • cis- if the two alkyl groups, R-, are on the same side of the C=C
    • trans- if the two alkyl groups, R-, are on opposite sides of the C=C.
    • these terms are inserted into the name as prefixes.

    cis-trans-

     

    For example,  but-2-ene, where both R = methyl :

     

    trans-but-2-ene cis-but-2-ene  

    Tri- or tetrasubstituted alkenes are described as cis- and trans- based on the relative arrangement of the groups that form the parent hydrocarbon carbon chain that gives the root name. In the example shown the below, the longest carbon chain that gives the root name is highlighted in blue:

    trans-3-methylhex-3-ene cis-3-methylhex-3-ene  

  • Question: What are polyesters?

    Posted in: Chemistry | Date: 18/01/2016

    Answer:

    A polyester is a polymer (a chain of repeating units) where the individual units are held together by ester linkages.

     

     

    The diagram shows a very small bit of the polymer chain and looks pretty complicated. But it isn't very difficult to work out - and that's the best thing to do: work it out, not try to remember it. You will see how to do that in a moment.

    The usual name of this common polyester is poly(ethylene terephthalate). The everyday name depends on whether it is being used as a fibre or as a material for making things like bottles for soft drinks.

    When it is being used as a fibre to make clothes, it is often just called polyester. It may sometimes be known by a brand name likeTerylene.

    When it is being used to make bottles, for example, it is usually called PET.

  • Question: How is water cooled in a soil pitcher? please tell

    Posted in: Physics | Date: 18/01/2016

    Answer:

    This is because of a physical process known as evaporation. When a liquid changes to a gaseous (or vapour) state without boiling, it is known as evaporation.

    A matka is made of mud and has many minute pores (extremely small holes). No matter how tightly you pack the mud, these pores remain. It is through these pores that the water, placed inside the matka, oozes out. Now, to evaporate, the water needs to absorb heat, which will change it to vapour.

    The only way the water oozing out of the matka can turn to vapour is by absorbing heat from the liquid within the matka and the matka itself. Due to this process of continuous absorption of heat from the water inside the matka, in a few hours, this water becomes cool.

  • Answer:

    J.R. Glauber, fused a mixture of the mineral pyrolusite and potassium carbonate to obtain a material that, when dissolved in water, gave a green solution (potassium manganate) which slowly shifted to violet potassium permanganate and then finally red. This report represents the first description of the production of potassium permanganate.Just under two hundred years later London chemist Henry Bollmann Condy had an interest in disinfectants, and marketed several products including ozonised water. He found that fusing pyrolusite with NaOH and dissolving it in water produced a solution with disinfectant properties. He patented this solution, and marketed it as Condy's Fluid. Although effective, the solution was not very stable. This was overcome by using KOH rather than NaOH. This was more stable, and had the advantage of easy conversion to the equally effective potassium permanganate crystals. This crystalline material was known as Condy’s crystals or Condy’s powder. Potassium permanganate was comparatively easy to manufacture so Condy was subsequently forced to spend considerable time in litigation in order to stop competitors from marketing products similar to Condy's Fluid or Condy's Crystals.

  • Question: Describe the process of sky wave propagation.

    Posted in: Physics | Date: 18/01/2016

    Answer:

    In radio communication, skywave or skip refers to the propagation of radio waves reflected or refracted back toward Earth from theionosphere, an electrically charged layer of the upper atmosphere. Since it is not limited by the curvature of the Earth, skywave propagation can be used to communicate beyond the horizon, at intercontinental distances. It is mostly used in the longwavefrequency bands.

    As a result of skywave propagation, a signal from a distant AM broadcasting station, a shortwave station, or—during sporadic E propagation conditions (principally during the summer months in both hemispheres)—a low frequency television station can sometimes be received as clearly as local stations. Most long-distance shortwave (high frequency) radio communication—between 3 and 30 MHz—is a result of skywave propagation. Since the early 1920s amateur radio operators (or "hams"), limited to lower transmitter power than broadcast stations, have taken advantage of skywave for long distance (or "DX") communication.

    Skywave propagation is distinct from:

    • groundwave propagation, where radio waves travel near Earth's surface without being reflected or refracted by the atmosphere—the dominant propagation mode at lower frequencies,
    • line-of-sight propagation, in which radio waves travel in a straight line, the dominant mode at higher frequencies.

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