Rk save Nature

                         📙1. Solid state  (II) Types of solids : 1) Crystalline solids: - regularity and periodicity. - sharp melting points. - cubic structure are anisotropic.  2) Amorphous solids: - randomly arranged. - temperature interval. - solids are isotropic. 3) Isomorphism and polymorphism: - i. Isomorphism : Two or more substances having the same crystal structure. Ex., NaF&MgO -ii. Polymorphism: single substance that exists in two or more forms or crystalline structures. Ex , calcite & aragonite. (III)Classification of crystalline solids: 1)Ionic crystals: - ionic crystals are charged ions. - ionic crystals are held by electrostatic force of attraction between oppositely charged ions. - Ionic crystals are hard and brittle. - They have high melting points. Ex., NaCL,KCL. 2) Covalent network crystals: -constituent particles in covalent network solids are atoms. -crystals are linked by a continuo...

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  Pollination: Pollen grains being non motile, angiosperms have evolved the strategy to use abiotic agents (wind, water) and biotic agents (birds, insects, snails) to their flowers, feeding the visitors and exploiting their mobility for pollination and also seed dispersal. Pollen grains are non-motile and they are usually carried from flower to flower by means of external agents. Pollination is the transfer of pollen grains from anther to the stigma of the flower. It is the pre- requisite for fertilization because both the male and female gametes are non-motile. Moreover gametes are produced at two different sites. a. Autogamy (self pollination) : It is a type of pollination in which bisexual flower is pollinated by its own pollen grains. Offsprings are genetically identical to their parents e.g. pea, Clitoria b. Geitonogamy: It is the transfer of pollen grain to a stigma of a different flower produced on the same plant. It is functionally similar to cross pollination as it involve...

  Antipodal cells are group of three cells present at the chalazal end. The two haploid polar nuclei of large central cell fuse to form diploid secondary nucleus or definitive nucleus, just prior to fertilization. This seven- celled and eight nucleated structure is called an embryo sac. This method of embryo sac development from a single megaspore is described as monosporic development. In angiosperms, the development of female gametophyte is endosporous i.e. within the megaspore. Female gametophyte is colourless, endosporic and is concealed in the ovule enclosed by ovary.

  Microsporogenesis : Each microspore mother cell divides - meiotically to form tetrad of haploid ■ microspores (pollen grains). Structure of microspore : Typical pollen grain is a non-motile, haploid, unicellular body with single nucleus. It is surrounded by a two layered wall called sporoderm. The outer layer exine is thick and made up of complex, non-biodegradable, substance called sporopollenin. It may be smooth or with a sculptured pattern (characteristic of the species). It is resistant to chemicals. At some places exine is very thin showing thin areas known as germ-pores. These are meant for the growth of emerging pollen tube during germination of pollen grain. The inner wall layer, intine consists of cellulose and pectin. Development of male gametophyte : Pollen grain marks the beginning of male gametophyte. It undergoes first mitotic division to produce bigger, naked vegetative cell and small, thin walled generative cell. The vegetative cell is rich in food and having irre...

  Sexual Reproduction:  It involves fusion of two compatible gametes or sex cells. All organisms reach to the maturity in their life before they can reproduce sexually. In plants, the end of juvenile or vegetative phase marks the begining of the reproductive phase and can be seen easily in the higher plants at the time of flowering. The flower is specialized reproductive structure of a plant in which sexual reproduction takes place. The function of flower is to produce haploid gametes and to ensure that fertilization will take place. Typical flower consists of four different whorls viz. calyx, corolla, androecium and gynoecium. The male reproductive whorl of flower is called androecium. Individual member of androecium, is called stamen. Stamen consists of filament, connective and anther. having two anther lobes (theca). Structure of Anther : Anther is generally dithecous (having two lobes) and tetrasporongiate. Each lobe of anther contains two pollen sacs. In dithecous anther ...

  Q . Transcription is the transfer of genetic information from a) DNA to RNA b) t RNA to m RNA c) DNA to m RNA d) mRNA to t RNA

  Q. Griffith worked on ..................... a) Bacteriophage b) Drosophila c) Frog eggs d) Streptococcus

Q.   Find the mis match pair:- a) Downs syndrome = 44+XY b) Turner's Syndrome = 44+X0 c). klinefelter's syndrome = 44+XXY d) Super female = 44+XXX

  Phenotypic ratio of incomplete dominance in Mirabilis Jalapa Solution: Caract option (b) 1:2:1

 

 

 Q.1. what does the negative sign indicates in Lenz's law? Solution:

  Q.1. what is isothermal process ? Solution:

  Q.1. what is attenuation in communication system? Solution:

Q.1.  Two Capacitors of capacities 5 Mf and 10 uf respectively are connected in series. Calculate the resultant Capacity of the Combination. Solution:

Q.1. In a Photoelectric experiment, the stopping Potential is 1.5V. What is the maximum kinetic energy of a Photoelectron? Solution: 

  What is surroundings in thermodynamics? Solution:  Ans.   In thermodynamics  "surroundings" sefer to everything outside of the system being studied 

  write the formula for torque acting on rotating Current carrying coil in terms of magnetic dipole moment, in vector form. Solution: 

  What is binding energy of a hydrogen atom ?  Solution: 13.6 eV

  12th class physics  Q.1. If the length of a potentiometer wire is increased by keeping constant potential difference across the wire, then ___. Solution:  Correct Option: (a) null point is obtained at larger distance.

12th class physics  Q.3.What is the resistance of an ideal voltmeter?  Solution: Resistance of an ideal voltmeter is Infinite 

 12th Biology  1.1 Asexual Reproduction: i. Fragmentation: Multicellular organisms can break into fragments due to one or the other reasons. e.g. Spirogyra. These fragments grow into new individuals. Fig. 1.1: Budding in Yeast ii. Budding: It is the most common method of asexual reproduction in unicellular Protosiphon and yeast. Usually it takes place during favourable conditions by producing one or more outgrowths (buds). These buds on separation develop into new individual. iii. Spore formation: In Chlamydomonas asexual reproduction occurs by flagellated, motile zoospores which can grow independently into new individuals. Vegetative Reproduction: Plants reproduce asexually through their vegetative parts. Hence, the new plants formed are genetically identical to their parents. There are also few methods which would not occur naturally in the plants. Agriculture and horticulture exploit vegetative reproduction in order to multiply fresh stocks of plants. Artificial methods are...

  12th class physics  Q.1. In biprism experiment , the distance of 20th bright band from the centrel bright band is 1.2 cm without changing the experimental setup , the distance of 30th bright band from the centrel bright band will be ____. Solution: Collect option: (d) 1.8 cm  Explanation : Given : 

          12th class physics  Q.1. The velocity of bob of a second's pendulum when it is 6 cm from its mean position and amplitude of 10 cm , is _____. Solution: Correct option : (a) 8π cm / s

  12th class physics  Q.1. The current in a coil changes form 50 A to 10 A in 0.1 second. The self inductance of the coil is 20 H . The induced e.m.f. in the coil is ____. Solution: Correct option : (d) 8000 v

  12th class physics  Q.1.In a ayclic process, if ∆u= internal energy. W = Work done , Q=Heat Supplied then____. Solution: Correct option : (d) w=Q

  12th class physics 

  12th class physics  Q.5.to Convert a moving coil galvanometer into an ammeter we need to connect a_____. Solution: Correct option: (a) small resistance in parallel with it.

  12th class physics Q.4. The work done in bringing a unit positive charge from infinity to a given Point against the direction of electric field lis known as____. Solution: Correct option : (c) electric.                                                potential 

  12th class physics  Q.3.The dimensional formula of surface tension is_____. Solution: Answer.- options (b) π/2

  12th class physics  The moment of inertia (MI) of a disce of radius R and Central axis is mass m about its______. (a)  (b) MR2/2 (C)  (d)