Rigid Body Rotation Question 2

Question :
A carpet of mass M made of inextensible material is rolled along its length in the form of a cylinder of radius R and is kept on a rough floor. The carpet starts unrolling without sliding on the floor when a negligible small push is given to it. Calculate the horizontal velocity of the axis of the cylinder part of the carpet when its radius is reduced to R/2.

For solution visit this link

How to apply law of conservation of energy in mechanics

We often comes across the problems in mechanics where we need to apply the law of conservation of energy where gravitational potential energy or gravity is involved . For solving such problems you can consider the following problem solving strategy,

1. First of all define the system which includes all the interacting bodies . Now choose a zero point for gravitational potential energy according to your convenience.
2. Select the body of interest and identify the point about which information is given in the question. Also identify the point where you want to find out asked quantity about the body of interest.
3. Check for the possibility of the presence of non-conservative forces. If there are no non-conservative forces present then write down the energy conservation equation for the system and identify the unknown quantity asked in the question.
4. Solve the equation for the unknown quantities asked in the question by substituting the given quantities in the equation obtained.

Mechanics :- Work and Energy (points to remember)

1. Work done on an object by a constant force F is
W=F.Δx
where F is the magnitude of the force, Δx is the magnitude of the displacement,and F and Δx point in the same direction.
SI unit of work : joule ( J) newton.meter
2. Work done is a simple number that is it is a scalar quantity not a vector. So there is no direction associated with it. Energy and energy transfer are also scalar quantities.
3. The kinetic energy KE of an object of mass m moving with a speed v is
defined by
T=1/2(mv²)
SI unit: joule ( J) kg.m²/s²
4. The net work done on an object is equal to the change in the object’s
kinetic energy: W_tot=T_f-T_i=ΔT
where the change in the kinetic energy is due entirely to the object’s change in speed
5. A force is conservative if the work it does moving an object between two points is the same no matter what path is taken.
6. The gravitational potential energy of a system consisting of the Earth and an object of mass m near the Earth’s surface is given by
V=mgy
where g is the acceleration due to gravity and y is the vertical position of the mass with respect to the surface of the Earth (or some other reference point).

Paramagnetic Substances

Paramagnetic substances are those materials which when placed in magnetic field becomes weakly magnetized in the direction of the external field. Some examples of paramagnetic substances are platinum, aluminium, chromium, manganese, copper sulphate, liquid oxygen etc. When a paramagnetic bar is placed in the magnetic field , the magnetic flux density in it is greater than the magnetic flux density B₀ in the vacuum. Thus the relative permeability of the paramagnetic substances is slightly greater then 1. The magnetic flux density due to magnetization is small but positive. The susceptibility of these substances decreases with increase in temperature. Paramagnetic substances are used in the measurement of low temperature.
Properties:-

• A paramagnetic bar , suspended between the poles of a magnet shows opposite poles to those of the magnet in its end.
• Paramagnetic substances have a tendency to move from weaker to the stronger parts in a non-uniform magnetic field.
• Paramagnetic substances obeys Curie's law  

Intensity of magnetization

• Intensity of magnetization is denoted by I
• It represents the extent to which the material is magnetized
• When we place a material in the magnetic field , atomic dipoles of the material tends to align fully or partially in the direction of the field.
• So, the net magnetic moment is developed in the direction of the field in any small volume of the material.
• Intensity of magnetization is defined as the magnetic moment per unit volume of the magnetized material. So, I=M/V , where M is the total magnetic moment within volume V due to the magnetizing field i.e., M=∑ m
• Unit of I is Am^-1

Free electron model of atom and energy bands in solids

• In atoms electrons orbits round the nucleus in their respective stable orbits.
• Coulomb force due to nucleus on outermost electrons known as valence electrons is negligible.
• These valence electrons are not bound with any particular atom and they are free to bind with any other atom in the crystal lattice.
• For full document visit this link

Superconductivity fact file

• Bulk superconductor in a week magnetic field will act as a perfect diamagnet , with zero magnetic induction in the interior.
• Nonmagnetic impurities have no marked effect on the SC transition temperature.
• A sufficiently strong magnetic field will destroy SC. At critical temperature critical field is zero H_C(T_C)=0
• Values of H_C are always low for type I superconductors.
• For a given H_C the area under magnetization curve is same for type II SC as for type I SC.
• In all SC entropy decreases markedly on cooling below transition temperature.
• Superconducting state is the more ordered state.
• Contribution to the heat capacity in the SC state is an exponential form with an argument proportional to -1/T
• In SC the important interaction is electron-electron interaction which orders the electrons in K space with respect to the fermi gas of the electrons.
• The argument of the exponential factor in the electronic heat capacity of a SC is found to be -E_g/2kT
• The transition in zero magnetic field from the superconducting state to the normal state is the second order phase transition, not involving any latent heat but discontinuity in heat capacity.
• Energy gap decreases continuity to zero as the temperature is increased to transition temperature.
• For photons of energy less than energy gap , the resistivity of the superconductor vanishes at absolute zero.
• As the temperature is increased not only does the gap decreases , but the resistivity for photon with energy below the energy gap no longer vanishes except at zero frequency.

Comparison between insulators and conductors

(1) Insulators

• Insulators have very wide forbidden energy gap nearly of the order of 5eV or more.
• Because of this very high energy gap it becomes impossible for electrons present in valence band to cross the gap and reach to the conduction band and this makes electrical conduction a practical impossibility in insulators at room temperature.
• However at very high temperatures or with very high voltage applied across the ends of the insulator , it may conduct and this is termed as breakdown of an insulator.

(2) Conductors

• Conduction band and valence band overlaps in case of a conductor.
• Value of forbidden energy gap is zero for conductors in other words it does not exists at all.
• For conductors or metals , valence band energies are same as conduction band energies and an valence electron can very easily become conduction electron (or, free electron) without any supply of heat energy.
• This is why metals contain large number of free electrons even at room temperature and are good conductor of electricity.

Continuous spectrum and characteristic X-Rays?

When energetic electrons bombard atoms in a metal target (for ex. tungsten) an electron may be ejected from innermost K-shell, the atom then is in exited state and is unstable. If an electron from L-shell now moves to vacancy in K-shell , the energy of atom is decreased and simultaneously there is emission of radiation. If E is the change in energy when electron moves from L-shell to K-shell then ,
E=hν where h is the plank's constant and ν is the frequency of radiation.
Thus , ν=E/h and for high energies , wavelength of the radiation is short and is of the order of 10^-8cm for X-Rays.
When we study X-Rays from a target it is observed to be a continuous spectrum with intense lines. These intense lines depends on the metal used as target and these are called characteristic X-Rays. The continuous spectrum depends on applied potential difference , current flowing in the filament and atomic number of target.

The Life and Death of Stars

I came across this article really a nice one and a must read if you are interested in knowing about stars.....

Astronomers believe that molecular clouds, dense clouds of gas located primarily in the spiral arms of galaxies are the birthplace of stars. Dense regions in the clouds collapse and form "protostars". Initially, the gravitational energy of the collapsing star is the source of its energy. Once the star contracts enough that its central core can burn hydrogen to helium, it becomes a "main sequence" star.

for more click the link given below......

physics.org | Explore | The Life and Death of Stars

Mass on inclined plane

Electromagnetic waves

1. The wave equation for light propagating in x-direction in vacuum may be written as
 E = E₀ sin ω(t-x/c)
Where E is the sinusoidally varying electric field at the position x at time t.
c is the speed of light in vacuum.
The electric field is in the Y-Z plane. It is perpendicular to the direction of propagation of the wave.
There is a sinusoidally varying magnetic field associated with the electric field when light is propagating. This magnetic field is perpendicular to the direction of wave propagation and the electric field E.
B = B₀ sin ω(t-x/c)
Such a combination of mutually perpendicular electric and magnetic fields constitute an electromagnetic wave in vacuum.

2. Maxwell developed the theory of electromagnetic wave.
 Maxwell generalised Ampere’s law to

∫B.dl = µ₀(i + i_d)


i_d = ε₀*(d Φ_E/dt)

Where

Φ_E/ = the flux of the electric field through the area bounded by the closed curve along which the circulation of B is calculated.

Maxwell termed i_d as displacement current

i  is current due to flow of charges is often called conduction current.

3. Ampere’s law without Maxwell’s modification is not valid if the electric field at the surface varies with time. The book gives the example of the region between capacitor plates to prove this point.


Continuity of electric current

Consider closed surface enclosing a volume a conductor in the shape of a cylinder. If all the charge entering it is leaving it, the conduction is continuous. But if some charge is accumulated inside the volume, this continuity breaks.

However, it we consider both conduction current as well as displacement current, the total current is still continuous.



Maxwell’s Equations

Gauss’s laws for electricity and magnetism, Faraday’s law and Ampere’s are collectively known as Maxwell’s equations

Gauss’s law of electricity

∮E.ds = q/ ε₀


Gauss’s law for magnetism

∮B.ds = 0

Faraday’s law

∮E.dl = -dΦ_B/dt

Ampere’s law

∮B.dl = µ₀(i + i_d)


i_d = ε₀*(d Φ_E/dt)

These equations are satisfied by a plane electromagnetic wave given by
E_y = E = E₀ sin ω(t-x/c)
B_z = B = B₀ sin ω(t-x/c)


In proving these equations we come to the formula that

c = i/√(µ₀ε₀)
the value calculated from this expression comes out to be 2.99793*10^8 m/s which was same as the experimentally measured value of speed of light in vacuum. This also provides a confirmatory proof that light is an electromagnetic wave.

Energy Density and Intensity 
For the waves described by

E_y = E = E₀ sin ω(t-x/c)
B_z = B = B₀ sin ω(t-x/c)

In any small volume dV, the energy of the electric field is

U_E = ½ ε₀E²dV

And the energy of the magnetic field is
U_B = B²dV/2µ₀

Total energy is

U = ½ ε₀E²dV + B²dV/2µ₀

When we substitute the values of E and B in the above equation and take an average over a longer period of time

u_av = ½ ε₀E₀² = B₀²/2µ₀

Intensity

The energy crossing per unit area per unit time perpendicular to the direction of propagation is called the intensity of a wave.

Consider a cylindrical volume with area of cross section A and length cΔt along the X-axis (the direction of propagation of the light wave).

The energy contained in this cylinder U = u_av(cΔt)A

As intensity if per unit area per unit time I = U/AΔt = u_avc.

In terms of maximum electric field (substituting the value of u_avc)

I = ½ ε₀E₀²c

Momentum

The electromagnetic wave also carries linear momentum with it. The linear momentum carried by the portion of wave having energy U is given by

p = U/c

If the wave incident on a material surface is completely absorbed, it delivers energy U and momentum p = U/c to the surface. Hence electromagnetic waves incident on a surface exert a force on the surface.


Electromagnetic Spectrum

Maxwell’s equations are applicable for electromagneticwaves of all wavelengths.

Basic source of electromagnetic waves is an accelerated charge.

Radio waves (used in radio and TV communication) are produced by charges accelerating in AC circuits having an inductor and capacitor.

Microwaves ( used for radar communication and in cooking) are also produced by such electric circuits with oscillating current.

Infrared waves (used in physical therapy) are produced by the atoms and molecules of hot bodies.

Visible light is also emitted by atoms under suitable conditions.

Ultraviolet radiation is emitted by atoms due to acceleration of electrons in the atom (the mechanism is same for visible light emission also).

The sun emits large amount of UV radiation. UV radiation is harmful to humans if absorbed in large amount.

X-rays (used in medical diagnosis) are produced when fast moving electrons collide with a metal target and decelerate. They are also harmful to living tissues.

Gamma rays are radioactive emissions from nuclei and have the shorted wavelengths among electromagnetic waves.

Electromagnetism Study material

Full length notes of following chapters are available at our website

1. Electro Magnetic induction link
2. Inductance link
3. Alternating current link

For more information visit http://physicscatalyst.com

Alternating current and Alternating EMF

• An alternating current is one whose magnitude changes sinusoidal with time .Thus alternating current is given by
  
  
  Where,
  i₀=current amplitude or peak value of alternating current
  If T is the time period of alternating current and f is the frequency, then
  
  
  Where ω is called angular frequency of A.C and φ is known as phase constant
  
• Instead of sine function AC can also be represented by cosine function and both representation leads to same results. We will discuss circuits with sine representation of A.C
  
• Figure below shows the variation of A.C with time
  
  
• Complete set of variations of the current in one time period T is called cycle
  
• The emf or voltage whose magnitude changes sinusoidal with time is known as alternating emf and is represented by
  
  
  where V₀ is the peak value of alternating current. 

Electric dipole problem

Question:
A point electric dipole having dipole moment p is placed in an external uniform electric field such that directions of dipole moment and electric field coincides. Find the radius of the sphere which forms one of the equi-potential surface enclosing the dipole.

Solution:

for solution visit this link

Electrostatic question 1 (electric potential)

Question:
There are two identical particles each of mass m crying a charge Q. Initially one of them is at rest and another charge moves with velocity v directly towards free particle. Find the distance of closest approach.
Solution:
This is an easy question what you simply have to do is apply the law of conservation of momentum and energy keeping in mind that velocity of both the particles are equal at the distance of closest approach. First try the question yourself and then look for the solution.
For solution of this question click this link

Generation Alzheimer’s: The Defining Disease of the Baby Boomers

This year, the first of the Boomer Generation turns 65 and with increased age comes increased risk of developing Alzheimer's disease. To bring urgently-needed attention to the risk facing the Boomers, the Alzheimer's Association recently released a groundbreaking study titled, Generation Alzheimer's: The Defining Disease of the Baby Boomers.

"Alzheimer’s is a tragic epidemic that has no survivors. Not a single one," said Harry Johns, president and CEO of the Alzheimer’s Association. "It is as much a thief as a killer. Starting this year, more than 10,000 baby boomers a day will turn 65. As these baby boomers age, one of out of eight of them will develop Alzheimer’s – a devastating, costly, heartbreaking disease. Increasingly for these baby boomers, it will no longer be their grandparents and parents who have Alzheimer’s – it will be them. It is estimated that 10 million baby boomers will end up developing Alzheimer's Disease.

In addition to the human toll, over the next 40 years Alzheimer’s will cost the nation $20 trillion, enough to pay off the national debt and still send a $20,000 check to every man, woman and child in America. And while every 69 seconds someone in America develops Alzheimer’s disease today, by 2050 someone will develop the disease every 33 seconds - unless the federal government commits to changing the Alzheimer’s trajectory.

Generation Alzheimer's: The Defining Disease of the Baby Boomers, sheds light on a crisis that is no longer emerging – but here. If you’d like to view a full copy of this report please visit www.alz.org/boomers.

The Alzheimer's Association is the world’s leading voluntary health organization in Alzheimer’s care, support and research. Our mission is to eliminate Alzheimer’s disease through the advancement of research; to provide and enhance care and support for all affected; and to reduce the risk of dementia through the promotion of brain heal

Send me your questions

Hi all,
All of us have problems in a subject like physics . So I invite you all to send me your queries at any of my mail address mailmephysics12@rediffmail.com or at physicsexpert12@gmail.com . I would try my best to solve your queries and would post them on my blog. If you have anything you want to share (related to physics, mathematics, chemistry, managing competitions etc.) with visitors of my blog feel free to mail me your article along with your link.
thanks
physics expert

Magnetic force on charged particle in a magnetic field

Question: Describe the magnetic force on the particle if it is at rest; it moves along  the direction of the magnetic field; it moves opposite the direction of the magnetic field; and if its at right angle with the direction of the magnetic field.
Answer:

1. In a magnetic field B, a particle of charge q and velocit v experiences a force,

F = q(v X B)

If v = 0, the F = 0 and hence the particle experiences no force.

(Here, bold letters represent vectors)

2. if the particle moves in the direction of the field then F=qvBsin(0) = 0 again particle does not experience any force when it move parallel to the magnetic field.

3. Again F=0 for the case when particle moves in a direction opposite to the field as 

F=qvBsin(180) = 0 since the angle between B and v is 180 degree.

4. In case B and v are both perpendicular to each other then charged particle will follow the circular path .

For detailed treatment visit http://physicscatalyst.com/magnetism/mag_0.php

Rigid Body Rotation Question 1

Question:
A rigid body of radius of gyration k, mass m and radius R rolls without slipping down a plane inclined at an angle θ  with the horizontal. (a) Find its acceleration and frictional force acting on it . (b) If the body were in the form of a disc and θ=30º , what will be the acceleration and the frictional force acting on it.

Solution:
for solution click this link

conceptual physics Centripital force

Hi all
I came across this video while browsing you tube and i like the way it explains about what is the concept of centripetal force.

How to calculate the direction of induced emf : Lenz's law

• The direction of induced current and emf is given by lenz's law.
  
• Due to change in magnetic flux through a closed loop an induced  current is established in the loop.
  
• Lenz's law states that
    'The induced current due to the induced emf always flow in such a direction as to oppose the change causing it'
  
• Now we can combine faraday's law  to find the direction of emf.
  
• Thus we can say that "The emf induced in a coil is equal to the negative rate of the change of the magnetic flux linked with it "
  
  
  
  
  
  

Explaination of lenz's law

• To explain this law again consider faradays experiment 1 in which north pole of the magnet  moves towards a closed coil.
  
• This movement of north pole of magnetic induces current in the coil in such a direction so that end of the coil ,facing and approaching north pole becomes a magnetic north pole.
  
• The repulsion between two poles opposes the motion of the magnet towards the coil.
  
• Thus work has to be done to push the magnet against  the coil.
  
• It is this mechanical work which causes the current to flow in the coil against its resistance R and supply
  the energy for the heat loss.
  
• The mechanical workdone is converted to electrical energy which produces the heat energy.
  
• If the direction of the induced current were such as not to oppsose the motion ,then we would be obtaining electrical energy continuously without doing any work ,which is impossible.
  
• So ,every things seems to be all right if we accept lenz's law otherwise the principle of conservation of the
  energy would be violated.
  
• Direction of the induced current can be found using Fleming right hand rule.
  " If we stretch thumb ,index  and middle finger  perpendicular to one another then index fingers points in direction of the magnetic field ,middle finger in direction of induced current and thum points in direction of the motion of the conductor"
  

Optics subjective question 1

Question
A narrow monochromatic beam of light of intensity I is incident on a glass plate A as shown below in the figure

Another identical glass plate B is kept close to A  and parallel to it. Each glass plate reflects 25% of the light intensity incident on it and transmits the remaining.Find the ratio of maximum and minimum intensities in the interference pattern formed by the two beams obtained after reflection from each plate.

Solution:

Hi First try to solve the question on your own it's an easy one . The answer is ratio of intensities is 49. I will provide the solution to this question.

For solution visit link

PN junction

• P-N junction is the basic building block of many semiconductor devices like diodes transistors etc.
• An P-N junction is formed when a P-type semiconductor is joined to a N-type semiconductor in such a way that the crystal structure remains continuous at the boundary.
• Three basic processes used for preparation of an P-N junction are alloying , growing and diffusion out of which diffusion is generally used for the preparation of an P-N junction.
• One very important characteristic of an P-N junction is its ability to conduct current only in one direction and the very high resistance it offers in another (or reverse direction).
• Consider the figure given below which shows a simple P-N junction having P type material towards left hand hand side and N-type material towards right hand side.
  
  
  
• P-type material have high concentration of holes and N-type material has high concentration of electrons. Along with these majority charge carriers both type of materials also consists of few minority charge carriers.
• As soon as P-N junction is formed holes begin to diffuse from P region to N region and electrons begin to diffuse from N region to P region and electron and holes begin to recombine in pairs.
• Due to diffusion and recombination of electrons and holes there remain no charge carriers near junction and this region known as depletion region is formed on both sides of the junction as shown in the figure.
• The thickness of this depletion region is of the order of one-tenth of micrometer.
• In depletion region there are stationary negative ions towards P side and positive ions towards N side.
• This creates a potential difference between two parts of the junction where N region is at higher potential with respect to P region .
• An electric field thus develops in this depletion region  which is directed from positive charged ions in N region towards negative charged ions in P region.
• Under the influence of this field electrons which are minority charged carriers in P side of the junction moves to N side and holes on N side of the junction moves to the P side.
• The motion of charged carriers due to this electric field is called drift.
• This internal electric field helping the movement of minority charged carriers adjust itself in such a way that drift of minority charged carriers across the junction is counterbalanced by the diffusion of same number of majority charged carriers across the junction thereby creating a state of equilibrium.

Phasor digrams

• Phasor diagrams are the diagrams representing alternating current and voltage of same frequency as vectors or phasors with phase angle between them.
• Phasors are the arrows rotating in the anti-clockwise direction i.e., they are rotating vectors but they represent scalar quantities.
• Thus alternatinc current and voltage varying sinusoidally can be represented by anticlockwise rotating vectors if they satisfy following conditions
  (i) length of the vector must be equal to the peak value of alternating voltage or current.
  (ii) vector representing alternating current and voltage would be at horizontal position at the instant when alternating quantity is zero.
  
• In certain circuits when current reaches its maximum value after emf becomes maximum then current is said to lag behind emf.
• When current reaches its maximum value before emf reaches its maximum value then current is said ti lead the emf.
• Figure given below shows the current lagging behind the emf by 90 degree.
  
  
  
  

Numerical for class 12 on electric field and potential

Question:
A thin stationary ring of 1 m has a positive charge of 1 x 10^-5C uniformly distributed over it. A particle of mass 0.9 gm and having a negative charge of 1 x 10^-6 C is placed on the axis at a distance 1 cm from the center of the ring. Show that the motion of the negatively charged particle is approximately simple harmonic. Calculate the time period of oscillation.

Solution:
For solution visit this link

What are Dielectrics

• A dielectric is an insulating material in which all nuclei are tightly bound to the nuclei of the atom.
• There are no free electrons in a dielectric material so they can not carry current.
• Electric conductivity of a dielectric material is very low and that of an ideal dielectric is zero.
• Some examples of dielectric materials are glass, plastic, mica, oil etc.
• Dielectric constant of a material is the ratio of the capacitance of the capacitor completely filled with the material to the capacitance of the same capacitor in the vacuum i.e. dielectric constant K=C/C₀.
• If the space between a capacitor is filled with a dielectric material capacitance of the capacitor increases.
• The value of dielectric constant K is independent of the shape and size of the capacitor and its value is different for different insulating materials.

For more information visit our website

Problem solving tricks-Right hand rules (Magnetic fields due to currents)

Right hand rule for cross product:-
Consider that c is the cross product of two vectors a and b i.e.,
c=a x b
If direction of vector a is along the x axis and that of b along z axis then direction of vector c could be find using right hand rule for cross products. With the thumb, index, and middle fingers at right angles to each other the first (index) finger can represent a, the first vector in the product; the second (middle) finger, b, the second vector; and the thumb, c, the product. So direction of vector c is perpendicular to the plane containing vectors a and b. This rule can be used in determining the directions of torque and angular momentum vectors and also to find the direction of the force on current carrying wire in an magnetic field.


Right hand thumb rule:-
This rule is used in situations when rotation is specified by a vector and we need to relate a curled element and a straight element , many such situations arises when you study magnetism. This can be done when you curl your fingers and straighten the thumb of your right hand. As an example you can consider an electric current passes through a straight wire. Here, the thumb points in the direction of the conventional current (from positive to negative), and the fingers point in the direction of the magnetic lines of flux.

Electromagnetic Induction (Motional EMF)

Kinematics problem

Question
A car accelerates from rest at a constant rate p for some time after which it decelerates at a constant rate q to come to rest. If total time lapse is t, find (1) the maximum velocity attained and (2) the total distance traveled.

Solution

For solution visit the link

Solved question on Structure of atom and Bohr atom model

Question:

Suppose that the potential energy between an electron and a proton at a distance r is given by -ke²/3r² . Use Bohr theory to obtain energy level of such a hypothetical hydrogen atom.

Solution:

For solution visit the link

CAPACITOR question with solution (Difficulty level : easy one)

Question-1:A Parallel Plate capacitor has following dimensions
Distance between the plates=10 cm
Area of Plate=2 m²
Charge on each plate=8.85 x 10^-10 C
Calculate following

1. Electric Field outside the plates
2. Electric Field Between the plates
3. Capacitance of the capacitor
4. Energy stored in the capacitor

ε₀=8.854 x 10^-12 C²N^-1m^-2
Solution-1:

As we know that Electric field outside the plates are zero
Electric field Inside the plates is
E=Q/ε₀A =50NC^-1

Capacitance=ε₀A/d =8.854 x 10^-12  x 2/.1=17.6 x 10^-11 F

Energy stored in capacitor=(1/2)Q²/C=.5 x 8.85 x 10^-10 x 8.85 x 10^-10/17.6 x 10^-11
=22.125 x 10^-10 J

Inertial and non inertial frames

• Both rest and motion are relative terms and there is nothing like absolute rest or absolute motion.
• Position or state of motion of a body may appear different in different frame of reference i.e.,  an object at rest in one frame of reference might appear to be in motion in another frame of reference.
• Newton's first law of motion also known as law if inertia does not always holds for all frame of reference and the frames in which this law holds good are called inertial frames of reference.
• Inertial frames of reference are non-accelerating frames this means that either they are fixed or move with constant velocity.
•  Non-inertial frames are the frames in which newton's law of inertia does not holds true. 
• Rotating and acceleration frame of references falls in the category of non inertial frames.
• In this frame acceleration is caused by fictitious or pseudo forces.

For more or full notes on kinematics visit this link

Hydrostatics question

Question
T what height h should a cylinder vessel of radius r be filled with a homogeneous liquid of density  to make the force , with which the liquid presses on the sides of the vessel equal to the force exerted by the liquid on the bottom of the vessel.

Solution

For solution visit the link

A question on Gauss's law

Question : A spherical liquid drop of radius r has charge q. If n number of such drops coalesces to form a single bigger drop , then on the surface of bigger drop what is
(1) charge
(2) charge density
(3) electric field and
(4) potential

This question is quite a easy one try and solve it though I'll provide the solution of this question.
For solution visit this link

Subjective Question Archive

Hi all,
I have given the link of most of the subjective questions in this blog under the tab "Subjective Question Archive" please visit the page and i hope you will definitely learn something or the other about solving questions in various topics in physics while going through these questions. Most of the questions given came along with their answers and solutions .
Hope you like the page
With best wishes for your exams
Physics Expert

Advantages an disadvantages of A.C. over D.C.

ADVANTAGES

1. The generation of A.C. is cheaper than that of D.C.
2. A.C. machines are simple , robust and do mot require much attention for their repairs and maintainance during their use.
3. Wide range of voltages are obtained by the use of transformer.
4. The magnitude of current can be reduced by using an inductance or a conductor without any appreciable loss of energy
5. A.C. can easily be converted into D.C. with the help of rectifiers.
6. When A.C. is supplied at higher voltages in long distance transmission , the line losses are small compared to a D.C. transmission

DISADVANTAGES

1. Peak value of A.C. is high and it is dangerous to use so better insulation is required.
2. It attracts person who touches it unlike D.C. which gives a repelling shock.
3. An A.C. is transmitted from surface of the conductor and hence need several strands of thin wires insulated from each other.

Physics for IIT-JEE,AIEEE ,PMT and Board examinations ,IIT-JEE Learning Material, IIT Preparation , IITJEE/AIEEE Test Series,IITJEE Online Study Material, Online Test Series, Online Coaching,Board Examination

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Physics study material for iitjee, aieee, pmt and board examination

PMT Focus : Assertion reason type questions

The following questions consists of two statements , Assertion and Reason. While answering these questions choose any of the following four responses
A. If both assertion and reason are true and the reason is correct explanation of assertion.
B. If both assertion and reason are true but reason is not a correct explanation of assertion.
C. If assertion is true and reason is false.
D. If both assertion and reason are false.

1. Assertion : In series LCR circuit , resonance occurs only at one frequency.
    Reason :  At this frequency inductive reactance is equal to capacitive reactance.
(a) A
(b) B
(c) C
(d) D

2. Assertion: Insulators do not allow the flow of current through themselves.
    Reason: They have no free charge carriers.

(a) A

(b) B

(c) C

(d) D

3. Assertion : When temperature of cold junction of a thermocouple is lowered , the value of neutral temperature of this thermocouple is raised
 Reason : When the difference of temperature of two junction is raised , more thermo e.m.f. is produced.

(a) A

(b) B

(c) C

(d) D

4. Assertion : If two parallel wires , hanging freely are connected to a battery in series , they come closer to each other.
Reason : Force of attraction acts between two wires crying charge 

(a) A

(b) B

(c) C

(d) D

5. Assertion : If an electron and proton enter an electric field with equal energy , then path of electron is more curved then that of electron.
 Reason : electrons has a tendency to form curve.

(a) A

(b) B

(c) C

(d) D

Answer:

1. a

2. a

3. d  here both assertion and reason are not true

4. d when two long parallel wires are connected to battery in series they carry current in opposite direction and hence repel each other.

5. d

Surface tension fact file

1. Those factors which increases cohessive forces between liquid molecules increases surface tension and those decreases cohesive forces decreases surface tension.
2. If impurity is completely soluble , then on mixing it in the liquid , its surface tension increases.
3. With the increase in temperature surface tension decreases.
4. Surface tension depands on the medium present on other side of the liquid surface.
5. The surface tension decreases due to electrification.
6. On mixing partial soluble impurities in a liquid , its surface tension decreases like mixing of detergent in water decreases surface tension of water.

Challenging mechanics problem : Kinematics

Question :
A body of mass m rests on horizontal table which has coefficient of static friction μ . It is desired to move the body by applying minimum possible force F. Find the magnitude and direction of the force F to which it has to be applied.
Solution :
For solution visit this link

Problem on Bohr atom model

Question:
A particle of charge equal to that of electron and mass 208 times the mass of electron (-meson)moves in a circular orbit around a nucleus of charge +3e (assume mass of nucleus to be infinite). Assuming that the Bohr atom model is applicable to this system
(a) derive an expression for the radius of the nth Bohr orbit
(b) find the value of n for which the radius of the orbit is approximately the same as that of the first Bohr orbit for the hydrogen atom
(c) find the wavelength of the radiation emitted when  -meson jumps from the third orbit to the first orbit (Rydberg constant = 1.097 x 107 m-1)  

Solution:

For solution click this link

how to choose your engineering college

Just scoring well in AIEEE is not enough. What is important is to choose the right field of engineering you wish to pursue and which college should you enroll? In this engineering admission season, Learnhub speaks to experts and students to help you choose the right college and stream of engineering. So get clicking to make the correct choice.
In this lesson, we will try to sort out your confusion on what should be the parameters to pick your engineering college. Should brand take precedence over placements or should faculty be given importance over infrastructure? Let's find out…
1) Faculty: If the faculty is good, the quality of education you will get will also be good. Important tips by experts to check out if the faculty of an engineering institute is good are -:
a) Review the number of faculty members with a PhD degree.
b) Check out the number of faculty members with an M.Tech degree.
c) Find out where your teachers have got their highest degrees. If it is from the same institute in which they are teaching, then the quality of education would not be very good.
d) Find out the faculty-student ratio: A small ratio would mean personalized attention and help you to perform well in academics.
e) Find out if your faculty members are active in research. These research-oriented teachers will normally have a better understanding of the latest developments in the area, and will therefore be in a position to explain better.
f) Number of workshops, seminars conducted by the institute also reflects the quality of an institute.
2) Accreditation: Your institute should be recognized by NAAC, AICTE or NBA. Accreditation is a process of quality assurance whereby programmes in an approved institution is critically apprised to verify whether that programme meets the norms and standards laid down. It is important if you are interested in studying further or even applying for a job/migrating abroad. Get the legal status of the degree you study for. If the school is not well-known, make sure that the degree is recognised.
3) Infrastructure: In fields like engineering, biotechnology and biology, having state-of-the-art and well equipped labs are a must. Also how good are the libraries, computer labs, projection room, etc? Also check out the sports, hostel facilities to know more about your institute.
4) Brand value: The names of some colleges, like IITs, NITs, is enough and have a high brand recall because of their quality of education. This is reflected by the achievements of their alumni and the research output of faculty and graduate students, other colleges have high brand recall due to advertising on a large scale. The brand of an institute also has an impact on its placements. Big companies will make a beeline for IITs and other renowned institutes than compared to other institutes of less repute. Also companies that recruit thousands of students from campuses every year would typically not go to campuses where they are likely to get just 5-10 potential employees.
5) Placements: Check out the campus placements graduates have got to get an understanding about the value of an institute. If big companies and MNCs are coming year after year to recruit students from that institute, it means that the quality of graduates is highly employable.
6) Location: Try to find an engineering institute in metros as there are better placements prospects. Talking about this, Saumil Shrivastava, an alumnus from IIT-Bombay, says, "Always try to go for an institute in Delhi, Mumbai or Bangalore as most big companies recruit engineering students from big cities as it is convenient from them."
7) Other factors -:
A) Status of the institute: A university status typically would mean greater academic freedom for innovation.
B) Updated curriculum
C) Renowned alumni
D) Extracurricular activities
E) A fully-residential campus usually provides a better learning environment.

Source: learnhub.com 

CSIR-NET and GATE physics: The Schrödinger wave equation

Want to know about Schrödinger wave equation follow the link given below

CSIR-NET and GATE physics: The Schrödinger wave equation: "OR read the document at this link"

Optics questions for PMT - pre medical exams

Or visit the link to see the full document.

Preparing physics pre-medicalexams

• For AIPMT test physics is one of the subject to prepare along with Biology and Chemistry. Physics for AIPMT and pre-med examination is usually easy in comparison to that of IITJEE and AIEEE.
•  If you have a grip over the concepts of physics then you should work on the speed and accuracy with which you attempt questions in this section.
• This speed and accuracy for attempting questions in physics comes with an experience.
• Students should use NCERT books for their preparation as these books are very clear in concepts and negligible amount of mathematics is required to understand these books.
• You could buy MCQ books by various authors available in market or you could also take simulated online test series to check your speed and accuracy.
• Practice lots of problems to gain confidence in the subject.
• Most important topics in physics are mechanics and modern physics.

kinematics: position and displacement

Here in this post i have mad an attempt to explain the concept of position , distance and displacement .Hope you like it

Tips for success

1. Find your own deep and compelling reason to successfully learn your subject and pass your exams.

2. Plan your time to include study, revision and social commitments - a balance of having fun, taking breaks and studying is vital.

3. Use multi-coloured Mind Maps® for your notes.

4. Review your notes regularly to reinforce your new-found knowledge.

5. Swiftly skim through your text books and course material before you read them in depth to give you an overview of your subject.

6. Learn how to remember lists of things by linking each item to a location on a journey or route you are familiar with around your town. You could even use your own home.

7. Before you do any revision, warm up by doing some gentle exercise to relieve any tension in your body and to get a rush of healthy oxygen flowing to your brain.

8. Do past papers under thorough exam conditions as often as possible to familiarise yourself with the format and the pressures of working under exam conditions.

9. In an exam, make sure you read the question completely and fully understand what the examiner wants before you allocate your time and begin answering the questions.

10. If you are faced with a mental block breathe deeply, relax and ask yourself "If I did know the answer to this question, what would it be?"

-memory expert
MICHEL TIPPER...................!!!!!!!!!!!http://www.michaeltipper.com/

Solved problem in physics (gravitation)

CSIR-NET and GATE physics: Free electron model of atom and energy bands in so...

CSIR-NET and GATE physics: Free electron model of atom and energy bands in so...

Nuclear Forces

We already know about gravitational and electrostatic forces now a question arises that does these forces still hold when we talk about nuclear dimensions as gravitational force between two protons is far too less to hold them and electrostatic force between two protons always a force repulsive in nature . So what hold protons together to form a nucleus. Answer is Nuclear forces which are attractive in nature and strong enough to overcome the electrostatic force of repulsion between two protons. So it is the nuclear forces which holds neutrons and protons (nucleons) together to form a nucleus. Nucleus forces are complex in nature and difficult to understand. Some of the properties of nuclear forces are given below.
(1) Nuclear forces are strong attractive forces :- These are strongest forces and are about 100 times stronger then electrostatic forces and about 10³⁸ times stronger then gravitational forces. These are the forces which holds nucleons in a nucleus.
(2) Nuclear forces are short range forces :- The nuclear forces are most effective up to a distance of the order of 10^-15m or less. These forces decreases rapidly as the separation distance between nucleons increases and becomes negligible when separation between nucleons is of the order of 10 fermi . The effective range up to which nuclear forces are effective is known as nuclear range.
(3) Nuclear forces are the charge independent :- Nuclear forces acting between two protons , two neutrons and between a proton and neutron have same strength and the nature of force is attractive.
(4) Nuclear forces are not central forces :- These forces do not obey inverse square law. The magnitude of nuclear force depends on the direction of spin of nucleons.
(5) Nuclear forces are saturated forces :- A nucleon experiences the force only due to it nearest neighbouring nucleons.

Challenging problem in capacitance

View the question here in this frame or visit the  link to see full document

How to master Physics

If you are a student then before attending your class do preparations for your lecture which means go through your text book , read the chapter and prepare for your forthcoming lecture.

Try never to miss your lectures and listen them carefully

Since you have read your lessen before you can easily clear your doubts and have discussion with your faculty.

Never forget to take your notes during your lecture.

After going home prepare a fresh copy of your notes and short notes of your lessen so that you can revise them easily while studying for your exams. Yes never forget to jot down your doubts and their possible explainations.

After compleating your chapter do not forget to practice related problems as they help you to clear your concepts. The more problems you solve the more comfortable you get with the subject.

Revise your lessen regularly so that it becomes impossible for you to forget the chapter.

Download SHM - Simple HArmonic Motion notes by physicscatalyst.com

For more notes and studdy material in physics visit http://physicscatalyst.com

Simple Harmonic motion (notes) -