Saturday, 30 April 2016

Some Essential Parts of an AC generator

  • Armature

Armature  is  a  rectangular  coil  consisting  of  a  large  number  of loops  or  turns  of  insulated  copper  wire  wound  over  a  laminated  soft iron core or ring. The soft iron core not only increases the magnetic flux but  also  serves  as  a  support  for  the  coil.
  • Field  magnets

The necessary magnetic field is provided by permanent magnets in the  case  of  low  power  dynamos.  For  high  power  dynamos,  field  is provided  by  electro  magnet.  Armature  rotates  between  the  magnetic poles such that the axis of rotation is perpendicular to the magnetic field.

  • Slip  rings

The  ends  of  the  armature  coil  are  connected  to  two  hollow metallic  rings  called  slip  rings.  These  rings  are  fixed  to a shaft, to which the armature is also fixed. When the shaft rotates, the slip  rings  along  with  the  armature  also  rotate.

  • Brushes

 There are two flexible metallic plates or carbon brushes. They provide  contact  with  the  slip  rings  by  keeping  themselves  pressed against  the  ring.  They  are  used  to  pass  on  the  current  from  the armature  to  the  external  power  line  through  the  slip  rings.

Limitation of Cyclotron

Limitations
  1.  Maintaining  a  uniform  magnetic  field  over  a  large  area  of  the Dees  is  difficult.
  2. At high velocities, relativistic variation of mass of the particle upsets  the  resonance  condition.
  3. At  high  frequencies,  relativistic  variation  of  mass  of  the electron  is  appreciable  and  hence  electrons  cannot  be  accelerated  by cyclotron.

Working Principle and construction of Cyclotron

Cyclotron is a device used to accelerate charged particles to high
energies. It  was  devised  by  Lawrence.
Principle
Cyclotron  works  on  the  principle  that  a  charged  particle  moving normal  to  a  magnetic  field  experiences  magnetic  lorentz  force  due  to
which  the  particle  moves  in  a  circular  path.
Construction
It   consists of  a hollow metal cylinder divided into two sections D1 and D2
 called Dees, enclosed in an evacuated chamber. The  Dees  are  kept separated and a source of ions is placed at  the  centre  in  the  gap between  the Dees. They  are  placed  between  the  pole pieces of a  strong  electromagnet.  The  magnetic field  acts  perpendicular  to  the  plane  of the  Dees.  The  Dees  are  connected  to a high frequency oscillator.

Working
When a positive ion of charge  q  and mass  m is emitted from the
source, it is accelerated towards the Dee having a negative potential at
that  instant  of  time.  Due  to  the  normal  magnetic  field,  the  ion
experiences magnetic lorentz force and moves in a circular path. By the
time  the  ion  arrives  at  the  gap  between  the  Dees,  the  polarity  of  the
Dees  gets  reversed.  Hence  the  particle  is  once  again  accelerated  and
moves into the other Dee with a greater velocity along a circle of greater
radius.  Thus  the  particle  moves  in  a  spiral  path  of  increasing  radius
and  when  it  comes  near  the  edge,  it  is  taken  out  with  the  help  of  a
deflector plate (D.P). The particle with high energy is now allowed to hit
the  target  T. When  the  particle  moves  along  a  circle  of  radius  r with  a
velocity v, the magnetic Lorentz force provides the necessary centripetal
force.
Limitations

  1.  Maintaining  a  uniform  magnetic  field  over  a  large  area  of  the Dees  is  difficult.
  2. At high velocities, relativistic variation of mass of the particle upsets  the  resonance  condition.
  3. At  high  frequencies,  relativistic  variation  of  mass  of  the electron  is  appreciable  and  hence  electrons  cannot  be  accelerated  by cyclotron.

Magnetic field due to a current carrying circular loop


A   cardboard is  fixed in a horizontal  plane.A  circular  loop
of  wire passes through  two  holes in the cardboard.Iron filings  are sprinkled  over  the cardboard. Current is  passed  through the   loop   and   the card board is gently tapped. It is observed that the iron filings arrange themselves along the resultant magnetic field. The magnetic lines of force are almost circular around the wire where it passes through the cardboard. At the centre of the  loop,  the  line  of  force  is  almost  straight  and  perpendicular  to  the plane of the                                                                                       circular loop.

Maxwells’s right hand cork screw rule


If  a  right  handed  cork  screw  is  rotated  to  advance  along  the direction  of  the  current  through a  conductor,  then  the  direction  of rotation  of  the  screw  gives  the  direction  of  the  magnetic lines  of  force around  the  conductor.

Magnetic field around a straight conductor carrying current


A  smooth  cardboard  with  iron  filings  spread over  it,  is fixed  in  a horizontal  plane  with  the  help of  a  clamp.
A  straight  wire  passes  through  a  hole made at  the  center
of  the  cardboard.
A current is passed through the  wire  by connecting  its ends to a  battery.
When   the cardboard is gently tapped, it is found that the iron filings  arrange  themselves  along  concentric  circles. This clearly shows that magnetic field is developed around  a  current  carrying  conductor.

To find the direction of the magnetic field, let us  imagine,  a  straight  wire  passes  through  the plane of the paper and perpendicular to it. When a compass needle is placed, it comes to rest in such a way that its axis is always tangential to  a  circular  field  around  the  conductor.
When  the  current  is  inwards the direction of the magnetic field around the conductor looks clockwise.
When the direction of the current is reversed, that it is outwards, the direction of the magnetic pole of the compass needle also changes showing the reversal of the direction of the magnetic field. Now, it is anticlockwise around the conductor. This proves that the direction of the  magnetic  field  also  depends  on  the  direction  of  the  current  in  the conductor. This is given by Maxwell’s rule.

Friday, 29 April 2016

Tsunami "the monster wave" Interesting facts and Information

Tsunami a Horrific things ever and ever.

What happen when the wave of tsunami strike to any city of  any country.
It's very horrific experience non of them ever wants to have such kind of experience
what ever comes under this wave yes Huge monster wave drag everything.

Tsunami travel with the average speed of 930 Km/hr.
I call it Ocean Monster.

Today I am going to open the some very interesting fact about tsunami
From ancient time in every where ocean are the great source of Natural resource.
But Beside this there is another face of Ocean when wave adopt the face of tsunami.
It is basically the large version of tidal wave.
How Any one can forgot year 26 dec 2004 , A black year
huge Natural disaster Tsunami in the Indian ocean that take away the life of about 280 thousand people in South Asia.

In Japan 11 March 2011 
there were a earthquake in side the water of the rate 9.3 mega thrust .
it cause the death of about the 18000 peoples and injured about 6500 peoples.
The height of wave was 120 ft and may reach to  1722 ft.
such a huge massive wave unimaginable .

Now How These way are generated 
  1. Land slide
  2. volcanic  eruption
  3. earthquake
when the tectonic plate of earth surface slip over one another then it releases not massive very massive amount of energy under water and it wakeup the sleeping sea.
This energy travel to the upper surface of water and displaces the water surface above the
sea level but due to gravity it again pull the displace water downward which make energy transmit outward in the form of very massive transverse wave.
It travel about 500 mile/hr.

when this high velocity wave come near the bank the depth of sea decrease, due to which these wave height start increasing.
it can rise up to 1750 ft above the normal sea level.
and it adopt the face of Monster Wave.

   

Thursday, 28 April 2016

Different Assumption made in the study of kenetic theory of gases



  1. molecule of gas moves all direction with all possible velocity during motion,the molecules colloid with one another but the collision do not effect the molecular density of gases
  2. The motion of molecules is random(the center of mass f gas remain at rest)
  3. Between two collisiona molecules move in straight line with uniform velocity this is because no force act on the particle b/w the collision.The distance covered by molecules is  called mean free path
  4. The diamension of the molecules may be neglected as compared to the dimension of free path.
  5. No approciable force of attraction or repulsion by molecule on in another accept during collision
  6. Collision between  melecules and with the wall of the container or perfectlly elastic and the time of impact is of neglagible duration (elastic collision means no change of linear momentum and kenetic energy ) elastic collision means no change of momentum but energy change
  7. Molecules obey newtons law of motion







Wednesday, 27 April 2016

Conversion of galvanometer into a voltmeter

Voltmeter   is   an   instrument used  to  measure  potential  difference between  the  two ends  of  a current carrying  conductor.

A  galvanometer      can      be converted    into    a    voltmeter    by connecting   a   high   resistance   in series with it. The scale is calibrated in  volt.  The  value  of  the  resistance connected  in  series  decides  the  range  of  the  voltmeter. Galvanometer  resistance  =  G
The  current  required  to  produce  full  scale  deflection  in  the galvanometer  =  Ig
Range  of  voltmeter  =  V
Resistance  to  be  connected  in  series  =  R
Since R is connected in series with the galvanometer, the current through  the  galvanometer,

Ig =  V/(R + G)

∴R  =  (V/Ig )–  G

From  the  equation  the  resistance  to  be  connected  in  series  with the  galvanometer  is calculated.
The  effective  resistance  of  the  voltmeter  is
Rv =  G  +  R

Rv is very large, and hence a voltmeter is connected in parallel in a circuit as it draws the least current from the circuit.
The  resistance  of  the  voltmeter  should  be  very  large  compared  to  the resistance  across  which  the  voltmeter  is  connected  to  measure  the potential difference. Otherwise, the voltmeter will draw a large current from  the  circuit  and  hence  the  current  through  the  remaining  part  of the circuit decreases. In such a case the potential difference measured by the voltmeter is very much less than the actual potential difference.The error is eliminated only when the voltmeter has a high resistance.
An  ideal  voltmeter  is  one  which  has  infinite  resistance

Definition of few Important quantities Thermal Equilibrium, Specific Heat, Water equivalent

Thermal Equilibrium
When two body is in contact and there is no transfer of heat between two body then bodies said to be in thermal equilibrium

Specific Heat
The amount of heat required to increase the temperature of unit mass of the substance by 1 degree centigrade is called specific Heat

Thermal capacity
it is defined as the amount of heat energy required to increase its temperature through 1 degree centigrade.

Its S.I unit is Joule/kelvin

Latent Heat

The heat energy released or absorbed at constant temperature per unit mass for change of state is called latent Heat.

Q = mL

L= latent heat
m= mass of substance

Water equivalent
It is the quantity of water whose thermal capacity is same as the heat capacity of body . it is denoted by W

W= ms

Hoar Frost

The conversion of solid into vapour state is called hoar frost

Sublimation
The direct conversion of solid into vapour state is called Sublimation.

Boiling point

It is the temperature at which liquid get boils is called boiling point

Melting Point

Conversion of solid into liquid at constant temperature is called Melting .



Surface tension and Surface energy

Its is the property of any type of liquid by virtue of which it try to minimize its surface area.
it is measured force acting on imaginary line per unit length that is drown tangential to the free surface of liquid

Mathematically given as
S = F/L = (work done)/(change in area)

It is scalar quantity
Surface tension is the molecular phenomenon cause due to cohesive force.

Surface tension of
liquid depend upon

  • Only Nature of liquid 


Surface tension of liquid is independent upon
  • The surface area of film  
Molecular Range 

the maximum distance upto which a molecule can exert a force of attraction or repulsion on other molecule is called molecular range

In solid and liquid it is of the order of 10^-9 m .

Surface energy

On increasing the free surface area of liquid ,work has to be done against the force of tension .
this work done stored in liquid surface as a potential energy .

This Additional potential energy per unit area of free surface of liquid is called surface energy.

surface energy = surface tension * increase in surface area .

Tuesday, 26 April 2016

Alpha, Beta and Gamma Rays Explanation

The  existence  of  the  three distinct  types  of  radiations,  α, β and γ−rays can be easily found by the following experiment.A small  amount  of  radium is placed  at  the  bottom  of  a  small hole drilled in a lead block, which is kept in an evacuated chamber


A photographic plate is placed at a short distance above the lead block. A strong magnetic field is applied at   right   angles   to   the   plane   of   the   paper   and   acting   inwards. Three distinct traces can be seen on the photographic plate when it is developed. The trace towards left is due to positively charged particles. They  are  named   α -particles.The  trace  towards  the  right  is  due  to negatively   charged   particles.They   are   named  β-particles.The undeviating trace is due to neutral radiations  which are called  γ−rays.If  an  electric  field  is  applied,  the  α-rays  are  deflected  towards  then negative  plate,β−rays  towards  the  positive  plate  and  γ−rays  are  not deflected.

Spectral series of Hydrogen atom


Spectral series of hydrogen atom

Whenever  an  electron  in  a  hydrogen  atom  jumps  from  higher energy  level  to  the  lower  energy  level,  the  difference  in  energies  of  the two  levels  is  emitted  as  a  radiation  of  particular  wavelength.  It  is called  a  spectral  line.
As  the  wavelength  of  the  spectral  line  depends upon  the  two  orbits  (energy  levels)  between which  the  transition  of electron  takes  place,  various  spectral  lines  are  obtained.  The  different wavelengths  constitute  spectral  series  which  are  the  characteristic  of the  atoms  emitting  them.  The  following  are  the  spectral  series  of hydrogen atom.

  •  Lyman series
  • Balmer series
  • Paschen series
  • Brackett series
  • Pfund series


Breif Explanation of Rutherford Model of atom

Rutherford  suggested  the  following  Model of  the  atom.


  1. Atom may be regarded as a sphere of diameter 10 angstrom  but whole of the positive charge and almost the entire mass of the atom is concentrated in a small central core called nucleus having diameter of about  10 to the power -14 m
  2.  As  the  atom  is  electrically  neutral,  the  total  positive  charge of  the  nucleus  is  equal  to  the  total  negative  charge  of  the  electrons  in it.
  3.  The  electrons  in  the  atom  were  considered  to  be  distributed around  the  nucleus  in  the  empty  space  of  the  atom.If  the  electrons were  at  rest,  they  would  be  attracted  and  neutralized  by  the  nucleus. To overcome this, Rutherford suggested that the electrons are revolving around  the  nucleus  in  circular  orbits,so  that  the  centripetal  force  is provided  by  the electrostatic  force  of  attraction  between  the  electron and  the  nucleus.

Drawbacks of Thomson Atomic Model

Drawbacks


  1. According  to  electromagnetic  theory,  the  vibrating  electron should  radiate  energy  and  the  frequency  of  the  emitted  spectral  line should  be  the  same  as  the  electron.  In  the  case  of  hydrogen  atom, Thomson’s model gives only one spectral line of about 1300 Å. But the experimental  observations  reveal  that  hydrogen  spectrum  consists  of five  different  series  with  several  lines  in  each  series.
  2. It  could  not  account  for  the  scattering  of  α-particles  through large  angles

Thomson atomic model




From  the  study  of  discharge  of  electricity through  gases,  it became  clear  that  an  atom consists of   positive   and   negative   charges J.J. Thomson  tried  to  explain  the arrangement  of positive  charge  and the    electrons    inside    the atom. According   to   him,   an   atom   is   a sphere  of  positive  charge  having  a radius  of the  order  of  10 angstrom.  The positive charge is uniformly distributed  over  the  entire  sphere  and  the  electrons  are  embedded  in the  sphere  of  positive  charge. The  total  positive charge inside the atom is equal to the total negative charge carried by the  electrons,  so  that  every  atom  is  electrically  neutral.According  to Thomson,  if  there  is  a  single  electron  in  the  atom( hydrogen  atom), the  electron  must  be  situated  at  the  center  of the positive sphere. For an atom with two electrons (helium atom), the electrons should be situated symmetrically with respect to the center of the  sphere  i.e opposite  sides  of  the  center  at  a  distance  of  2r,  where r  is the radius of the positive sphere. In a three electron system of the atom, the electrons should be at the corners of a symmetrically placed equilateral  triangle,  the  side  of  which  was  equal  to  the  radius  of  the sphere.   In   general,   the   electrons   of   an   atom are located in   a symmetrical  pattern  with  respect  to  the  center  of  the  sphere. It  was  suggested  that  spectral  radiations  are  due  to  the  simple harmonic  motion  of  these  electrons  on  both  sides  of  their  mean positions. Moreover, the stability of the atom was very well explained on the  basis  of  this  model.


Tangent galvanometer

Tangent galvanometer

Tangent  galvanometer  is a device used for measuring current. It works on the principle of tangent law. A magnetic needle suspended at a point where  there  are  two crossed fields at right angles to each other will come to rest in the direction of the resultant of the two fields.

Construction

It consists of a circular coil of wire wound over a non magnetic frame of brass or wood.The vertical frame is mounted on a horizontal circular turn table provided with three leveling screws. The vertical frame can be rotated about  its vertical diameter. There is a small upright projection at the center of  the turn table  on which a compass box is supported. The compass  box  consists  of  a  small  pivoted  magnet  to  which  a thin  long  aluminium  pointer  is  fixed  at  right  angles.  The  aluminium pointer can move over a circular scale graduated in degrees. The scale consists of four quadrants. The compass box is supported such that the center  of  the  pivoted  magnetic  needle  coincides  with  the  center  of  the coil.  Since  the  magnetic  field  at  the  center  of  the  coil  is  uniform  over a  very  small  area,  a  small  magnetic  needle  is  used  so  that  it  remains in an uniform field even in deflected position. Usually the coil consists of three sections of 2,5 and 50 turns, which are of different thickness, used  for  measuring  currents  of  different  strength.

Theory

When  the  plane  of  the  coil  is  placed  parallel  to  the  horizontal component of Earth’s magnetic induction and a current is passed  through  the  coil,  there  will  be  two  magnetic fields  acting  perpendicular  to  each  other (1) the  magnetic  induction  (B)  due  to  the  current in the coil acting normal to the plane of the coil and  (2)  the  horizontal  component  of  Earth’s magnetic  induction  (Bh),Due   to   these   two   crossed   fields,   the pivoted  magnetic  needle  is  deflected  through an  angle θ. According  to  tangent  Law,
B  =  Bhtanθ........(1)
If a current I passes through the coil of n turns and of radius a, the  magnetic  induction  at  the  center  of  the  coil  is
B  =  μnI/2a...........(2)
Substituting  equation  (2)  in  equation  (1)μnI/2a=  Bhtanθ
∴. I  =  (a2B/μn) *tan  θ
I  =  K tanθ...................(3)
where  K  = 2aBh/μn  is  called  the  reduction  factor  of  the  tangent galvanometer. It is a constant at a place. Using this equation, current in  the  circuit  can  be  determined. Since  the  tangent  galvanometer  is  most  sensitive  at  a  deflection of  45 degree, the  deflection  has  to  be  adjusted  to  be  between  30  and  60 degree.

Monday, 25 April 2016

Laws of photoelectric emission

Laws  of  photoelectric  emission

The experimental observations on photoelectric effect may be summarized  as follows,which  are  known as the fundamental laws of photoelectric emission.

  • There is a minimum frequency called the threshold frequency, for a given photo sensitive  material,below which emission of photoelectrons stops completely.
  • For a given photosensitive material,the photo electric current is directly proportional to the intensity of the incident radiation,provided the frequency is greater than the threshold  frequency.
  • The photoelectric emission is an instantaneous process. i.e. there is no time lag between the incidence of radiation and the emission of  photo electrons.
  • The maximum kinetic energy of the photo electrons is directly proportional to the frequency of incident radiation,but is independent of  its intensity.

Hallwachs Experimental Setup and Explanation

Hallwachs Experimentset-up

Experimentset-up to study the photo electric effect is shown  in  Fig. It  consists  of  an  evacuated quartz  bulb  with  two  zinc  plates  cathode and  anode.  The  plates  are  connected  to  a battery  and  a  sensitive  galvanometer.  In  the absence   of   any   radiation   incident   on   the plates.There  is  no  flow  of  current  and  hence there  is  no  deflection  in  the  galvanometer. But,when  an  electro  magnetic  radiation  like ultraviolet  radiation  is  allowed  to  fall  on  the cathode plate which  is  connected  to  the  negative terminal  of  the  battery, a  current  begins  to flow,indicated  by  the deflection  in  the  galvanometer But,  when  ultraviolet  radiation  is made  to fall  on  anode there  is  no  deflection  in  the  galvanometer.  These observations reveal that the particles emitted by the cathode plate  due to the photoelectric  effect  are  negatively  charged.  These  particles  were  found to  be  electrons.  The  observed  current  known  as  the  photoelectric current  is  due  to  the  flow  of  electrons.After  the  study  of  photoelectric  effect  by  Hallwachs,  scientists J.J.Thomson, Lenard, Richardson, Compton did a series of experiments to  study  the relationship  between  photoelectric  current,  intensity  ofincident   radiation,   velocity   and   the   kinetic   energy   of   the   photo electrons,   and   their   dependence   on   the   wave   length   of   incident radiation used.

Photoelectric effect


Photoelectric effect

Photoelectric emission is the phenomena by which a good number
of  substances, chiefly  metals,emit  electrons  under  the  influence  of radiation such as γ rays, X-rays, ultraviolet and even visible light. This effect  was  discovered  by  Heinrich  Hertz  in  1887  while  working  with resonance electrical circuits. Hallwachs,Elster and Geitel investigated the phenomenon with a simple experimental arrangement after one year.


What is Holography and Maser

Holography

When an object is photographed by a camera, a two dimensional
image  of  three  dimensional  object  is  obtained.  A  three  dimensional
image   of   an   object   can   be   formed   by   holography.   In   ordinary
photography,  the  amplitude  of  the  light  wave  is  recorded  on  the
photographic film. In holography, both the phase and amplitude of the
light waves are recorded on the film. The resulting photograph is called Hologram

MASER
The   term   Maser   stands   for   Microwave   Amplification   by
Stimulated  Emission  of  Radiation.  The  working  of  maser  is  similar  to
that of laser. The maser action is based on the principle of population
inversion  followed  by  stimulated  emission.  In  maser,  the  emitted
photon, during the transition from the metastable state belongs to the
microwave  frequencies.  The  paramagnetic  ions  are  used  as  maser
materials. Practical maser materials are often chromium or gadolinium
ions doped as impurities in ionic crystals. Ammonia gas is also a maser
material.  Maser  provides  a  very  strong  tool  for  analysis  in  molecular spectography

Different application of X-ray

Applications of X–rays
X–rays  have  a  number  of  applications.  Some  of  them  are  listed-
Scientific research
  1. X–rays are used for studying the structure of crystalline solids and alloy
  2. X–rays  are  used  for  the  identification  of  chemical  elements including  determination  of  their  atomic  numbers
  3. X–rays  can  be  used  for  analyzing  the  structure  of  complex molecules  by  examining  their  X–ray  diffraction  pattern.

Medical applications

  1. X–rays  are  being  widely  used  for  detecting  fractures,  toumers, the  presence  of  foreign  matter  like  bullet  etc.,  in  the  human  body.
  2. X–rays  are  also  used  for  the  diagnosis  of  tuberculosis,  stones in  kidneys,  gall  bladder  etc.
  3. Many  types  of  skin  diseases,  malignant  sores,  cancer  and toumers  have  been  cured  by  controlled  exposure  of  X-rays  of  suitable quality.
  4. Hard X–rays are used to destroy toumers very deep inside the body.

Industrial applications

  1.  X–rays are used to detect the defects or flaws within a material
  2. X–rays  can  be  used  for  testing  the  homogeneity  of  welded joints,  insulating  materials  etc.
  3. X-rays  are  used  to  analyse  the  structure  of  alloys  and  the other  composite  bodies. 
  4. X–rays  are  also  used  to  study  the  structure  of  materials  like rubber,  cellulose,  plastic  fibre etc.


Soft X–rays and Hard X–rays

Soft X–rays and Hard X–rays
X–rays  are  of  two  types-
  •  Soft  X–rays  
  • Hard  X–rays


Soft  X–rays
X–rays  having  wavelength  of  4Å  or  above,  have  lesser  frequency
and  hence  lesser  energy.  They  are  called  soft  X  –  rays  due  to  their  low
penetrating  power.  They  are  produced  at  comparatively  low  potential
difference.

 Hard  X–rays
X–rays  having  low  wavelength  of  the  order  of  1Å have  high
frequency  and  hence  high  energy.  Their  penetrating  power  is  high,
therefore   they   are   called   hard   X–rays.   They   are   produced   at
comparatively  high  potential  difference.
The wavelength of X–rays depends upon the kinetic energy of the
electrons  producing  them  and  this  kinetic  energy  depends  upon  the
potential  difference  between  the  filament  and  the  target.

Determination of specific charge (e/m) of an electron – Thomson’s method.

Determination  of  specific  charge  (e/m)  of  an  electron  –
Thomson’s method.

In  1887, J.J.  Thomson,  measured  the  specific  charge  (e/m)  of
the  cathode  ray  particles.  The  specific  charge  is  defined  as  the  charge
per  unit  mass  of  the  particle.  Thomson  discovered  that  the  value  of
(e/m)  was  independent  of  the  gas  used  and  also  independent  of  the
nature  of  the  electrodes.

Principle
The  fact  that  the  cathode  rays  (electrons)  are  deflected  by
electric  and  magnetic  fields  is  made  use  of  in  this  method.
Experimental arrangement

A  highly  evacuated  discharge  tube  used  in  this  experiment.
Cathode rays are produced by the discharge between the cathode and the anodes.
A thin pencil of cathode
ray comes out through fine pin
holes  in  the  anode  discs.  The
cathode   rays   then   pass
between  two  parallel  metal
plates as shown in figure
 and strike the flat  face  of  the  tube.  This  face
is   coated   with   suitable
fluorescent material. A spot of
light  is  produced   But  when  a  potential  difference  V  is  applied
between tow plates, the beam is deflected By the use of a pair
of  coils,  uniform  magnetic  field  is  produced  perpendicular  to  the  plane
of  the  paper  and  outwards  through  out  the  region  between vertical deflection plates.

Wednesday, 20 April 2016

Impulsive force and Impulse of a force

Impulsive  force  and  Impulse  of  a  force

(i)  Impulsive  Force
An impulsive force is a very great force acting for a very short time
on a body, so that the change in the position of the body during the time
the  force  acts  on  it  may  be  neglected.
(e.g.) The blow of a hammer, the collision of two billiard balls etc.

(ii)  Impulse  of  a  force
The  impulse  J  of  a  constant  force  F
acting for a time t is defined as the product
of  the  force  and  time.
(i.e)  Impulse  =  Force×time
               J=F×t
The impulse of force F acting over a time interval t
is  defined  by  the  integral,

J=F∫dt  (0 to t)

When a variable force acting
for  a  short  interval  of  time,  then  the  impulse  can  be  measured  as,
J  =  F average×dt

Type of Inertia

The  inertia  is  of  three  types
(i)Inertia  of  rest
(ii)    Inertia  of  motion
(iii)   Inertia  of    direction.
(i)     Inertia  of  rest

It  is  the  inability  of  the  body  to  change  its  state  of  rest  by  itself.
Examples
(i)  A  person  standing  in  a  bus  falls  backward  when  the  bus
suddenly starts moving. This is because, the person who is initially at
rest  continues  to  be  at  rest  even  after  the  bus  has  started  moving.
(ii) A book lying on the table will remain at rest, until it is moved
by  some  external  agencies.
(iii) When a carpet is beaten by a stick, the dust particles fall off
vertically downwards once they are released and do not move along the
carpet  and  fall  off.
(ii)  Inertia  of  motion
Inertia  of  motion  is  the  inability  of  the  body  to  change  its  state  of
motion  by  itself.
Examples
(a) When a passenger gets down from a moving bus, he falls down
in  the  direction  of  the  motion  of  the  bus.
(b) A passenger sitting in a moving car falls forward, when the car
stops  suddenly.
(c)  An  athlete  running  in  a  race  will  continue  to  run  even  after
reaching  the  finishing  point.
(iii)  Inertia  of  direction
It  is  the  inability  of  the  body  to  change  its  direction  of  motion  by
itself.
Examples
When a bus moving along a straight line takes a turn to the right,
the  passengers  are  thrown  towards  left.  This  is  due  to  inertia  which
makes the passengers travel along the same straight line, even though
the  bus  has  turned  towards  the  right.
Assumption with kenetic theory of gases

1-The molecule of gas moves all direction with all possible velocity during motion,the molecules colloid with one another but the collision do not effect the molecular density of gases
2-The motion of molecules is random
(the center of mass f gas remain at rest)
3-Between two collisiona molecules move in straight line with uniform velocity this is because no force act on the particle b/w the collision.The distance covered by molecules is  called mean free path

4-The diamension of the molecules may be neglected as compared to the dimension of free path.
5-No approciable force of attraction or repulsion by molecule on in another accept during collision
6-Collision between  melecules and with the wall of the container or perfectlly elastic and the time of impact is of neglagible duration
(elastic collision means no change of linear momentum and kenetic energy )
elastic collision means no change of momentum but energy change

7-Molecules obey newtons law of motion