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Channel Posts
Chemistry
1. What is the chemical formula of calcium carbonate?
कैल्शियम कार्बोनेट का रासायनिक सूत्र क्या है?
| 2 | 2. A wave has a frequency of 50 Hz and a wavelength of 2 m. What is its speed?
एक तरंग की आवृत्ति 50 हertz और तरंगदैर्ध्य 2 मीटर है। इसकी गति क्या है? | 531 |
| 3 | Physics
1. What is the principle behind the working of a transformer?
ट्रांसफॉर्मर के कार्य करने का सिद्धांत क्या है? | 456 |
| 4 | 2. A wave is traveling through a medium with a speed of 300 m/s. If the frequency of the wave is increased by 20%, what will be the effect on its wavelength? | 410 |
| 5 | Physics
1. A particle is moving in a circular path with a constant speed. If the radius of the circle is doubled, what will be the effect on its centripetal acceleration? | 377 |
| 6 | 🟣 Probability: Key Concepts
▪️ An experiment is said to be a random experiment if there is more than one possible outcome, and it is impossible to predict the outcome in advance.
▪️ All possible results of an experiment are called its outcomes.
▪️ Let us consider an experiment of rolling a die. All possible outcomes are 6, 5, 4, 3, 2, or 1. The set of all these outcomes {6, 5, 4, 3, 2, 1} is known as the sample space and is denoted by ‘S’.
▪️ Let us consider an experiment of tossing Two coins once. Since the coin can turn up Tail or Head, therefore, all the possible outcomes are:
▪️ Both coins – Head = HH, Both coins – Tail = TT, First coin – Head and Second coin – Tail = HT, First coin – Tail and Second coin – Head = TH.
▪️ Thus, the sample space (S) can be represented as {HH, TT, HT, TH}.
▪️ For any random experiment, let S be the sample space. The probability P is a real-valued function whose domain is the power set of S and [0, 1] is the range interval.
▪️ For any event E, P(E) ≥ 0
▪️ P(S) = 1
▪️ If E and F are mutually exclusive events, then P(E ∪ F) = P(E) + P(F). | 492 |
| 7 | 🟤 Conservation of Mechanical Energy
The capacity to do work is known as energy. We have heard of many types of energy like mechanical energy, potential energy, chemical energy, kinetic energy, thermal energy, solar energy, and many more. In this article, let us discuss in detail the conservation of mechanical energy.
🔺 What is Mechanical Energy?
Mechanical energy is the sum of kinetic energy and potential energy in an object that is used to do a particular work. In other words, it describes the energy of an object because of its motion or position, or both.
Let us consider the example of an ideal simple pendulum (friction-less). We can see that the mechanical energy of this system is a combination of its kinetic energy and gravitational potential energy. As the pendulum swings back and forth, a constant exchange between the kinetic energy and potential energy takes place. When the bob attains its maximum height, the potential energy of the system is the highest, whereas the kinetic energy is zero. At the mean position, the kinetic energy is the highest, and the potential energy is zero. Between these two extreme points, we see that the system possesses both kinetic and potential energy, the sum of which is constant. These observations tell us a lot about the conservation of mechanical energy. But how can we prove it for every other system? In the next section, we shall learn more about the conservation of mechanical energy using a suitable example.
🟥 Conservation of Mechanical Energy
According to the principle of conservation of mechanical energy,
The total mechanical energy of a system is conserved i.e., the energy can neither be created nor be destroyed; it can only be internally converted from one form to another if the forces doing work on the system are conservative in nature.
In order to understand this statement more clearly, let us consider an example of one-dimensional motion of a system. Here a body, under the action of a conservative force F, gets displaced by Δx, then from the work-energy theorem, we can say that the network done by all the forces acting on a system is equal to the change in the kinetic energy of the system.
Mathematically, ΔKE = F(x) Δx
Where, ΔK is the change in kinetic energy of the system. Considering only conservative forces are acting on the system Wnet = Wc.
Thus Wc = ΔKE
Also, If conservative forces do the work in a system, the system loses potential energy equal to the work done. Hence, Wc = -PE.
Which implies that the total kinetic energy and potential energy of a system remains constant if the process involves only conservative forces.
KE + PE = constant
KEi+ PEi = KEf+ PEf
Where denotes the initial values and f denotes the final values of KE and PE.
This law applies only to the extent that the forces are conservative in nature. The mechanical energy of the system is defined as the total kinetic energy plus the total potential energy. In a system that comprises only conservative forces, each force is associated with a form of potential energy and the energy only changes between the kinetic energy and different types of potential energy, such that the total energy remains constant. | 421 |
| 8 | 🟣 Le Chatelier’s Principle
It states that change in any factor, such as concentration, pressure, temperature, etc., causes the equilibrium to shift in such a direction to counteract or reduce the effect of a change.
Effect of Concentration Changes on Equilibrium and Product Formation
➖ As per Le Chatelier’s principles, the only way for equilibrium to accept more reactants is to increase product formation. The forward reaction is favoured when the concentration of the reactant is increased. The equilibrium of the reaction shift towards the use of reactants in the reaction, which decreases the concentration of the reactants.
➖ Similarly, the addition of product (concentration/pressure) shall increase the backward reaction to decrease the product concentration. The backward reaction is favoured when the concentration of the reactant decreases, the equilibrium of the reaction shift towards the production of reactants, and the concentration of the reactants is more.
Example:
Consider a reaction between oxygen and sulfur dioxide to produce sulfur trioxide.
2SO2(g) + O2(g) ⇋ 2SO3(g)
If the concentration of the reactant increases, then
Equilibrium will shift towards the decrease in the concentration of the reactants.
More favoured for the forward reaction.
Some of the SO2 or O2 form SO3.
Equilibrium of the reaction shift towards the right.
If the concentration of the reactant decreases, then
Equilibrium will shift towards the increase in the concentration of the reactants.
More favoured for the backward reaction.
Some of the SO3 would change to SO2 or O2.
Equilibrium of the reaction shift towards the left.
If the product decreases, then
The equilibrium of the reaction shift to increase the concentration of the sulfur trioxide.
Increase in the forward reaction rate.
Some of the SO2 or O2 form SO3.
Equilibrium of the reaction shift towards the right.
If the product increases, then
The equilibrium of the reaction shifts to decrease the concentration of the sulfur trioxide.
Increase in the reverse reaction rate.
Some of the SO3 would change to SO2 or O2.
Equilibrium of the reaction shift towards the left. | 340 |
| 9 | 🔴 Ionic Compound & Crystal Lattice
The crystal lattice is an ordered arrangement of an ionic compound which is pictured as a three-dimensional aggregation of negative and positive ions. There exists a charge balance between the negative and positive ions in a crystalline solid. The enthalpy of lattice formation stabilizes the crystal lattice. | 331 |
| 10 | 🟣 Lone Pairs Of Electrons
A few atoms which are bonded have an extra pair of electrons which are not involved in bonding. Such electrons are called lone pairs of electrons. Lewis dot structure represents the arrangement of lone pairs and bonded pairs around each atom of a molecule. | 318 |
| 11 | What is the difference between 1D and 2D motion?
1D motion means motion in One dimension. That is, the body moves only on one axis, either x, y or Z. Or simply, it moves only linearly. In contrast, 2D motion involves motion which is defined as the combination of two axes. | 360 |
| 12 | What is known as the fundamental quantity?
Certain quantities have been chosen as fundamental quantities because physics is considered to be quantitative science. They are:
➖ Length
➖ Mass
➖ Time
➖ Electric Current
➖ Thermodynamic Temperature
➖ Amount of Substance
➖ Luminous Intensity | 343 |
| 13 | ✅ Common terminologies used – Structure of Atom
Electrons – These subatomic particles orbit around the nucleus. They are negatively charged particles and found in definite energy levels orbiting the nucleus.
Protons – These subatomic particles are found in the nucleus. They are positively charged particles and belong to the nucleon group.
Neutrons – These subatomic particles are found in the nucleus. They are neutral particles and belong to the nucleon group.
Rutherford model – It states that during a chemical reaction, the mass of the products and reactants will always be equal.
Bohr model – The model states that electrons orbit stable around the nucleus in certain fixed circular orbits at a distinct distance from the nucleus. These orbits are related to specific energies and are also referred to as energy levels or energy shells.
Heisenberg uncertainty principle – The Heisenberg Uncertainty Principle states that the simultaneous determination of the velocity and position of a particle is impossible.
Shells – A pathway followed by the electron to move around the nucleus of the atom.
Subshells – A pathway for the electron to move within a shell. | 346 |
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| 15 | ✅ CBSE Class 12 Physics Notes - Electrostatic Potential and Capacitance
What Is Electrostatic?
The electrostatic potential is referred to the force which is external but conservative. It is the work done by an external force in bringing a charge s from a point r to a point p. It is the difference in the potential energy of charges between the initial and final points.
Potential
The potential of a point is referred to the work done per unit charge in bringing a charge from infinity to a certain point.
Equipotential Surface
It is a type of surface over which potential has a constant value. When seen as a point charge, concentric spheres centred at a particular location of the charge are equipotential surfaces.
Potential Energy
The potential energy stored in a system is the work done by the external influence in organizing the charges in their locations.
Polarisation
The plates of a capacitor enclose a medium which can be filled with insulating substances, and then a net dipole moment is induced by the electric field in the dielectric. This gives rise to the field in the opposite direction.
Capacitor
A capacitor is a system of two conductors separated by an insulating material. | 331 |
| 16 | ✅ Physics Class 12: Electrostatics
Charge is a property of matter that causes it to produce and experience electrical and magnetic effects. The subject of the electrical effect of charges at rest is called electrostatics. When both electrical and magnetic effect are present, the interaction between charges is referred to as electromagnetic.
There exist two types of charges in nature: positive and negative. Like charges repel, and unlike charges attract.
The SI unit of charge is the coulomb (C). It is defined in terms of electric current. One coulomb is the charge transferred in one second across the section of wire carrying a current of one ampere.
q = It
⇒1C = (1A) (1s)
The reason is that one can make precise measurements of the current flowing in wire, whereas the charge on a body tends to leak away.
The coulomb is a very large amount of charge. A typical charge acquired by a rubbed body is 10−8C, whereas a lightning bolt may transfer as much as 20 C between the earth and a cloud.
Quantization of Charge
Electric charges appear only in discrete amounts, it is said to be quantized. The quantum of charge, first directly measured in 1909 by R. A. Millikan, is approximately
e = 1.602 × 10−19 C
A charge q must be an integer multiple of this basic unit. That is q = 0, ±e, ±2e, ±3e etc Although the mass of the proton is about 1800 times greater than that of the electron, their charges have the same magnitude.
qe = − e ; qp = + e
Note that the electron itself is not the charge: Charge is a property, like mass, of elementary particles, such as the electron.
Conservation of Charge
For an isolated system, the total charge remains constant, charge is neither created nor destroyed, it is transferred from one body to the other.
By ‘isolated’ we mean that there are no paths, such as wires or damp air, by which charges can leave or enter the system. To apply the law of conservation of charges, we add up the number of elementary charges before the interaction and then again after it. For example,
In a chemical reaction
Na+ + Cl− → NaCl
(+e) + (−e) = (0)
In a radioactive decay
n → p + e− + ν (antineutrino)
(0) = (+e) + (−e) + (0)
Invariance of Charge
The numerical value of an elementary charge is independent of velocity. It is provided by the fact that an atom is neutral. The difference in masses of an electron and a proton suggests that electrons move much faster in an atom than protons. If the charges were dependent on velocity, the neutrality of atoms would be violated. | 413 |
| 17 | Chromatography
Substances can be selectively adsorbed from solution, and an application of this fact is now widely used in analysis for carrying out separations which would involve very lengthy and difficult procedures by ordinary chemical method under the name chromatography. | 338 |
| 18 | Characteristics of chemisorption
(i) High specificity: Chemi−sorption is highly specific and it will only occur if there is some possibility of chemical bonding. For example, oxygen is adsorbed on metals by virture of oxide formation and hydrogen is adsorbed by transition metals with unpaired d−orbitals leading to hydride formation.
(ii) Nature of gas: Chemisorption will occur if there is some possibility of chemical action between the gas and the solid adsorbent.
(iii) Irreversibility: As chemisorption involves compound formation, it is commonly irreversible in nature. Chemisorption is also an exothermic process but the process is very slow at low temperatures on account of high energy of activation. Like most chemical changes, it often increases with rise of temperature. A gas adsorbed at low temperature by physical adsorption may change into chemisorption at high temperature.
High pressure is favourable for chemisorption.
(iv) Surface area: Like physical adsorption, chemisorption also increases with increase of surface area of the adsorbent.
(v) Heat of adsorption: Heat of adsorption is high enough (80−240 kJ mol–1 or
20−60 kcal mol–1) as chemisorption involves chemical bond formation. | 339 |
| 19 | Characteristics of physical adsorption
(i) Lack of specificity: A given surface of an adsorbent does not show very strong attraction for a particular gas as the van der Waals forces are universal.
(ii) Nature of gas : The amount of gas adsorbed by a solid depends on the nature of gas. In general more easily liquefiable gases is adsorbed to a greater extent.
(iii) Reversible nature : Physical adsorption of a gas by a solid is generally reversible. The gas adsorbed can be removed by reversing the conditions temperature and pressure. Thus, more of gas is absorbed when pressure is increased as the volume of the gas decreases and it can be removed by decreasing pressure. Since the adsorption process is exothermic, the physical adsorption occurs readily at low temperature and decreases with increasing temperature (Le−Chatelier’s principle). As the activation energy in the physical adsorption is more or less zero, the rate of adsorption is not affected even at low temperature.
(iv) Surface area of adsorbent: The extent of adsorption increases with increase of surface area of the adsorbent. Thus, finely divided metals and porous substances having large surface areas as good adsorbents.
(v) Heat of adsorption: No doubt, physical adsorption is an exothermic process but it heat of adsorption is quite low (20−40) kJ mole-1 since the attraction between gas molecules and solid surface is due to weak van der Waal’s forces. | 295 |
| 20 | Types of Adsorption
There are two types of adsorption of gases on solids.
(i) Physical Adsorption (ii) Chemical Adsorption
If accumulation of gas on the surface of a solid occurs on account of weak van der Waal’s forces, the adsorption termed as physical adsorption or physisorption. When the gas molecules or atoms are held to solid surface by chemical bonds, the adsorption is termed chemical adsorption or chemisorption. The chemical bonds may be covalent or ionic in nature. | 329 |
