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Starting early is the key to success, here is a list of tricks to crack JEE Main:
1. Dedicated study plan: Devise a strategy for JEE Main and stick to it thoroughly so that each topic gets sufficient practice and revision.
2. Maximize speed: As a JEE Main aspirant it is important to develop a good speed so try to solve at least 70-80 numerical every day.
3. Time to clear doubts: If you stumble upon a concept and can’t figure the way out, it is best to take help from your mentors or co-JEE Main aspirants. This will not only help you with the concept but also inform you of any flaws in your study pattern.
4. Aim for JEE Advanced: It is best to aim for JEE Advanced and not just limit your preparations to JEE Main. As the syllabus for both the exams is almost same, studying to clear JEE Advanced will help you cover most of the JEE Main syllabus in depth.
5. Balance between coaching and self-study: If coaching takes up 3-4 hours each day then put aside at least 2-3 hours for self study too. This balance is necessary to revise/ practice concepts and prepare for the next class.
6. Practice makes you perfect: Once you have understood the concept, go for solving question banks and test series. This is the best way to know the trend of questions to be expected at JEE Main. There is no way you can crack JEE by just memorizing concepts if you do not know how to apply them.
7. Paper solving strategy: You need to identify what strategy works best for you to solve the JEE Main. For instance, during mocks, if solving toughest questions first, then less difficult and keeping the easiest for the last works for you then go ahead with it, otherwise find what method helps you get accurate results in shortest time.
8. Passionate about becoming an IITian: If IIT is your goal then keep your enthusiasm up by considering your studies as the most satisfying and content hours of the day.
9. Quality time for studies: Irrespective of number of hours you study, give it your 100 percent. A half-baked preparation will never work out, so study smart instead of prolonging the hours you sit in front of the books.
10. Refresh button: Relax and take breaks during your hectic study timetable. Use this time to rejuvenate yourself, watch a movie, listen to some songs, or play a sport. This will help you to stay focused and feel fresh.
Apart from these tips, it is important to keep practicing test papers. It will teach you how to approach JEE mains question paper.
Best of luck for your preparations.

ELECTROPHILIC SUBSTITUTION


Background
Electrophilic substitution happens in many of the reactions of compounds containing benzene rings - the arenes. For simplicity, we'll only look for now at benzene itself.

Note: Before you start it would be a good idea if you had a clear idea about the structure of benzene. Check your syllabus now to find out what you need to know, and then read the page on the modern orbital view of benzene in the organic bonding section of this site. Don't forget to look in the section(s) in your syllabus on bonding as well as organic chemistry.
Haven't got a syllabus? If you are working towards a UK-based exam (A level or its equivalent), follow this link to find out how to get one.

This is what you need to understand for the purposes of the electrophilic substitution mechanisms:

Benzene, C6H6, is a planar molecule containing a ring of six carbon atoms each with a hydrogen atom attached.

There are delocalised electrons above and below the plane of the ring.

The presence of the delocalised electrons makes benzene particularly stable.

Benzene resists addition reactions because that would involve breaking the delocalisation and losing that stability.

Benzene is represented by this symbol, where the circle represents the delocalised electrons, and each corner of the hexagon has a carbon atom with a hydrogen attached.


Electrophilic substitution reactions involving positive ions
Benzene and electrophiles

Because of the delocalised electrons exposed above and below the plane of the rest of the molecule, benzene is obviously going to be highly attractive to electrophiles - species which seek after electron rich areas in other molecules.

Species: A useful word which can mean any particle you want it to mean - an atom, a molecule, an ion or a free radical.

The electrophile will either be a positive ion, or the slightly positive end of a polar molecule.

Help! If you aren't sure what a polar molecule is, read about electronegativity and polar bonds before you go on.
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The delocalised electrons above and below the plane of the benzene molecule are open to attack in the same way as those above and below the plane of an ethene molecule. However, the end result will be different.

If benzene underwent addition reactions in the same way as ethene, it would need to use some of the delocalised electrons to form bonds with the new atoms or groups. This would break the delocalisation - and this costs energy.

Note: You can read about electrophilic addition to ethene if you are interested.
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Instead, it can maintain the delocalisation if it replaces a hydrogen atom by something else - a substitution reaction. The hydrogen atoms aren't involved in any way with the delocalised electrons.

In most of benzene's reactions, the electrophile is a positive ion, and these reactions all follow a general pattern.

The general mechanism

The first stage

Suppose the electrophile is a positive ion X+.

Two of the electrons in the delocalised system are attracted towards the X+ and form a bond with it. This has the effect of breaking the delocalisation, although not completely.

Note: If you aren't sure about the use of curly arrows in mechanisms, you must follow this link before you go on.
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The ion formed in this step isn't the final product. It immediately goes on to react with something else. It is just an intermediate.

There is still delocalisation in the intermediate formed, but it only covers part of the ion. When you write one of these mechanisms, draw the partial delocalisation to take in all the carbon atoms apart from the one that the X has become attached to.

The intermediate ion carries a positive charge because you are joining together a neutral molecule and a positive ion. This positive charge is spread over the del

Substitution Nucleophilic unimolecular (S 1)
This reaction is carried out in polar protic solvents such as water,
alcohol, acetic acid etc. This reaction follows first order kinetics.
Hence, this is named as substitution nucleophilic unimolecular.
This reaction takes place in two steps as described below:
1. In step 1, the bond between carbon and halogen breaks due
to presence of a nucleophile and formation of carbocation
takes place. It is the slowest and the reversible step as huge
amount of energy is required to break the bond. The bond is
broken by solvation of the compound in protic solvent, thus
this step is slowest of all. The rate of reaction depends only
on haloalkane not on nucleophile.
2. In step 2, the nucleophile attacks the carbocation formed
in step 1 and the new compound is formed.
Since, the rate defining step of the reaction is formation of
carbocation, hence greater the stability of formation of
intermediate carbocation, more is the ease of the compound
undergoing substitution nucleophilic unimolecular or S 1
reaction. In case of alkyl halides, 3 alkyl halides undergo S 1
reaction very fast because of the high stability of 3
carbocations. Hence allylic and benzylic halides show high
reactivity towards the S 1 reaction.

Substitution Nucleophilic bimolecular (S 2)
This reaction follows second order kinetics and the rate of
reaction depends upon both haloalkane as well as participating
nucleophile. Hence this reaction is known as substitution
nucleophilic bimolecular reaction. In this reaction, the
nucleophile attacks the positively charged carbon and the
halogen leaves the group. Both the formation of carbocation
and exiting of halogen take place simultaneously. In this
process, unlike S 1 mechanism the inversion of configuration is
observed. Since this reaction requires the approach of the
nucleophile to the carbon bearing the leaving group, the
presence of bulky substituents on or near the carbon atom has a
dramatic inhibiting effect. So opposite to S 1 reaction
mechanism, this is favoured by mostly by primary carbon, then
secondary carbon and then tertiary carbon.

's law
The total of the electric flux out of a closed surface is equal to the charge enclosed divided by the permittivity.The electric flux through an area is defined as the electric field multiplied by the area of the surface projected in a plane perpendicular to the field. Gauss's Law is a general law applying to any closed surface. It is an important tool since it permits the assessment of the amount of enclosed charge by mapping the field on a surface outside the charge distribution. For geometries of sufficient symmetry, it simplifies the calculation of the electric field. Another way of visualizing this is to consider a probe of area A which can measure the electric field perpendicular to that area. If it picksany closed surface and steps over that surface, measuring the perpendicular field times its area, it will obtain a measure of the net electric charge within the surface, no matter how that internal charge is configured.

A perfectly elastic collision is
defined as one in which there
is no loss of kinetic energy in
the collision. An inelastic
collision is one in which part
of the kinetic energy is
changed to some other form
of energy in the collision. Any
macroscopic collision between
objects will convert some of
the kinetic energy into internal
energy and other forms of
energy, so no large scale
impacts are perfectly elastic.
Momentum is conserved in
inelastic collisions, but one
cannot track the kinetic energy
through the collision since
some of it is converted to
other forms of energy.
Collisions in ideal gases
approach perfectly elastic
collisions, as do scattering
interactions of sub-atomic
particles which are deflected
by the electromagnetic force.
Some large-scale interactions
like the slingshot type
gravitational interactions
between satellites and planets
are perfectly elastic.
Collisions between hard
spheres may be nearly elastic,
so it is useful to calculate the
limiting case of an elastic
collision. The assumption of
conservation of momentum as
well as the conservation of
kinetic energy makes possible
the calculation of the final
velocities in two-body
collisions.
Elastic collisions, target at rest
Elastic Collisions
An elastic collision is defined
as one in which both
conservation of momentum
and conservation of kinetic
energy are observed. This
implies that there is no
dissipative force acting during
the collision and that all of the
kinetic energy of the objects
before the collision is still in
the form of kinetic energy
afterward.
For macroscopic objects which
come into contact in a
collision, there is always some
dissipation and they are never
perfectly elastic. Collisions
between hard steel balls as in
the swinging balls apparatus
are nearly elastic.
"Collisions" in which the
objects do not touch each
other, such as Rutherford
scattering or the slingshot
orbit of a satellite off a planet,
are elastic collisions. In
atomic or nuclear scattering,
the collisions are typically
elastic because the repulsive
Coulomb force keeps the
particles out of contact with
each other.
Collisions in ideal gases are
very nearly elastic, and this
fact is used in the
development of the
expressions for gas pressure
in a container.

The ability of some neutral atoms, molecules, and free radicals to capture additional electrons and thereby become negative ions. For each specific type of particle, this ability is measured by the quantity S, known in English simply as the electron affinity. 5 is equal to the energy difference between the neutral atom or molecule in the ground state and the ground state energy of the negative ion formed after the addition of the electron.
For most atoms, the ability to add an electron results from the atoms’ outer electron shells not being filled (see). Such atoms include H atoms and elements of Group I of the periodic table, which have one outers electron, and also atoms of groups III, IV, V, VI, and VII, which have incomplete shells. The capture of an additional electron by Fe, Co, and Ni atoms, which in the normal state have two outer electrons, is generally believed to lead to the filling of a free position in the inner 3d shell.The value of S has been accurately determined for only a few atoms; the data on the S of molecules and radicals are, for the most part, insufficiently reliable. The 5 of atoms can be measured directly, for example, by determining the wavelength of light λ0corresponding to the threshold of photo detachment of an electron from the negative ion:S=hcλ0, where his Planck’s constant and c is the speed of light. The values of S for C, O, S, I, and Cl atoms have been established by this method. The use of the surface ionization effect(the vaporization of halogen atoms from the surface of incandescent W) to measure 5 has not yet yielded accurate values of 5. The reason for this failure is that, because of the polycrystalline structure of W, the work function is not the same on different parts of the surface. When two atoms are vaporized from the same surface and become negative ions, the difference in the 5 of the two atoms can be determined with much higher accuracy. Typical values ofSfor atoms, in electron volts (eV), are as follows: H, 0.754; C, 1.25; 0, 1.46; S, 2.1; F, 3.37; Cl, 3.65; Br, 3.35; and 1,3.08. Thevalues of 5 for molecules and radicals vary over a wide range. In many cases they amount to fractions of an eV. Larger values, however, are also found: NO2, > 3 eV; OH~2 eV; and CN,

just like the resistor, the capacitor, sometimes referred to as a condenser,is a simple passive device that is used to “store electricity”. The capacitor is a component which has the ability or “capacity” to store energy in the form of an electrical charge producing a potential difference (Static Voltage) across its plates, much like a small rechargeable battery.There are many different kinds of capacitors available from very small capacitor beads used in resonance circuits to large power factor correction capacitors, but they all do the same thing, they store charge.In its basic form, a capacitor consists of two or more parallel conductive(metal) plates which are not connected or touching each other, but are electrically separated either by air or by some form of a good insulating material such as waxed paper, mica,ceramic, plastic or some form of a liquid gel as used in electrolytic capacitors. The insulating layer between a capacitors plates is commonly called the dielectric.

The Bohr model was a one-dimensional model that used one quantum number to describe the distribution of electrons in the atom. The only information that was important was the size of the orbit, which was described by thenquantum number. Schr�dinger's model allowed the electron to occupy three-dimensional space. It therefore required three coordinates, or threequantum numbers, to describe the orbitals in which electrons can be found.The three coordinates that come from Schr�dinger's wave equations are the principal (n), angular (l), and magnetic (m) quantum numbers. These quantum numbers describe the size, shape, and orientation in space of the orbitals on an atom.Theprincipal quantum number(n) describes the size of the orbital. Orbitals for whichn= 2 are larger than those for whichn= 1, for example. Because they have opposite electrical charges, electrons are attracted to the nucleus of the atom. Energy must therefore be absorbed to excite an electron from an orbital in which the electron is close to the nucleus (n= 1) into an orbital in which it is further from the nucleus (n= 2). The principal quantum number therefore indirectlydescribes the energy of an orbital.Theangular quantum number(l) describes the shape of the orbital. Orbitals have shapes that are best described as spherical (l= 0), polar (l= 1), or cloverleaf (l= 2). They can even take on more complex shapes as the value of the angular quantum number becomes larger.There is only one way in which a sphere (l= 0) can be oriented in space. Orbitals that have polar (l= 1) or cloverleaf (l= 2) shapes, however, can point in different directions. We therefore need a third quantum number, known as themagnetic quantum number(m), to describe the orientation in space of a particular orbital. (It is called themagneticquantum number because the effect of different orientations of orbitals was first observed in the presence of a magnetic field.)

Electric Potential energy potential energy can be defined as the capacity for doingworkwhich arises from position or configuration. In the electrical case, a charge will exert a force on any other charge and potential energy arises from any collection of charges. For example, if a positive charge Q is fixed at some point in space, any other positive charge which is brought close to it will experience a repulsive force and will therefore have potential energy.The potential energy of a test charge q in the vicinity of this source charge will be:Showwhere k isCoulomb's constant.In electricity, it is usually more convenient to use the electric potential energy per unit charge, just calledelectric potentialor voltage.Application:Coulomb barrier for nuclear fusionEnergy in electron voltsIndexVoltage conceptsHyperPhysics*****Electricity and MagnetismR NaveGo BackZero PotentialThe nature of potential is that the zero point isarbitrary; it can be set like the origin of a coordinate system. That is not to say that it is insignificant; once the zero of potential is set, then every value of potential is measured withrespect to that zero. Another way of saying it is that it is the change in potential which has physical significance. The zero of electric potential (voltage) is set for convenience, but there is usually some physical or geometric logic to the choice of the zero point. For a singlepoint chargeor localized collection of charges, it is logical to set the zero point at infinity. But for an infinite line charge, that is not a logical choice, since the local values of potential would go to infinity. For practical electrical circuits, the earth orground potentialis usually taken to be zero and everything is referenced to the earth.Zero of potential at infinity

Pascal's Laws relates to pressures in fluids - liquid or gaseous state:*.if the weight of a fluid is neglected the pressure throughout an enclosed volume will be the same*.the static pressure in a fluid acts equally inall directions*.the static pressure acts at right angles to any surface in contact with the fluidExample - Pressure in an Hydraulic CylinderThe pressure of2000 Pain an hydraulic cylinder acts equally on all surfaces. The forceon a piston with area0.1 m2can be calculated asF = p A (1)whereF = force (N)p = pressure (Pa, N/m2)A = area (m2)or with valuesF = (2000 Pa) (0.1 m2)=200(N)Example - Force in a Hydraulic JackThe pressure acting on both pistons in a hydraulic jack is equal.The force equation for the small cylinder:Fs= p As (2)whereFs= force acting on the piston in the smallcylinder (N)As= area of small cylinderp = pressure in small and large cylinderThe force equation for the large cylinder:Fl= p Al (2b)whereFl= force acting on the piston in the large cylinder (N)Al= area of large cylinderp = pressure in small and large cylinder(2) and (2b) can be combined toFs/ As= Fl/ Al (2c)orFs= FlAs/ Al (2d)The equation indicates that the effort force required in the small cylinder to lift a load on the large cylinder depends on the area ratio between the small and the large cylinder - the effort force can be reduced by reducing the small cylinder area compared to the large cylinder area.