ALL PHYSICS DOUBTS - POST HERE !!

[Fastal]

guys is
P=hdg only applicable to liquids
cuz i used that formula for air pressure in a past paper

[2010]

what questions ? ill explain them to you if i can

Actually  my teacher told me that we should try solving papersds from 1995 onwards because they are repeating questions from old papers..
There's no specific question....i'm just not able to solve any question related to radioactivity (from scattering to isotopes to hteir absorbing properties)

[WARRIOR]

Actually  my teacher told me that we should try solving papersds from 1995 onwards because they are repeating questions from old papers..
There's no specific question....i'm just not able to solve any question related to radioactivity (from scattering to isotopes to hteir absorbing properties)

       ATOMIC PHYSICS.
You should know verythign is made of extreemtly small atoms and at the centre there is a nucleas Which contain nucleons ( protons + neutrons )  .Around the nuclease there are electrons but we totally ignore that they exist in physics ( atomic anway )
You should know the charge and atomic mass unit
          charge             masss
Electrons -1              1/1840 ..which is basically zero and you can say that in exmas  
protons  + 1               1
nuetron  - 0                1

We have elements and we have proton numbers  ( DOWN )  6 and mass number  (UP) 14
Proton number tells you the amount of protons adn electron                                                      14
Mass number ttells what is in the nucleus ( protons + neutrons ). So for exacmple , If element is C
                                                                                                                                       6
the proton number down ( 6 ) which means also has 6 protons and eleectron . The mass number up, tellls us proton + nucleans and we know proton therefore neutron = 14-6=8

ISOTOPS
ATOMS OF SAME ELEMENT WITH DIFFEENT NUCLEON NUMBER BUT SAME PROTON NUMBER
               127                         131
EX  IODINE                      IODINE
          53                               53

IM COMPLETEING ..HOLD ON

[WARRIOR]

EVIDENCE FOR THE NUCLEAR MODEL

THE GOLD EXPERIMENT ( ALPHA PARTICLES ARE + )
ALPHA PARTICLES WRER FIRE THROUGH VERY THIN GOLD FOIL AND A DETECTOR WAS MOVED AROUND THE FOIL TO CHECK THE MOVEMENTS ( I.E DEFLECTION - TWISTS - ETC)

http://www.iop.org/activity/education/Teaching_Resources/Teaching%20Advanced%20Physics/Atomic%20and%20Nuclei/Images%20500/img_mid_5329.gif

this is whats happening ^ ..you see the yellow point in the middle of of the clouds,, see how small the nucleus is compared to it?

ANYWAY  YOU HAVE TO EXPLAIN WHAT IS GOING ON !

THE ALPHA PARTICLES GOING STRAIGHT WIHTOUT DEFLECTION TELLS  THAT THE ATOM IS NEARLY ALL EMPTY!! SPACE APART FROM THE NUCLEUS!  AND SO..

THE ALPHA PATICLES  THAT WERE DEFLECTED BY SMALL ANGLES SHOW US THAT THE NUCLEAS WHICH REPELLED ALPHA PARTICLS WHICH PASSED VERY VERY VERY VERY VERY CLOSE TO IT GOT REPELLED ..TELLS US THAT NUCLEUS IS POSOTIVE. AND SO

THE ALPHA PARTICLES (ABOUT 1 IN 8000 ) WERE SURPRISINGLY BOUNCED BACK !!!!!!!!!!!!!!!!> THIS TELLS US THAT THE ALPHA PATICLES COLLIDED WITH THE TINY WEENY TINY WEENY  POSITIVE NUCLEASE , SO IT TELLS US THAT IT HAS A LAAAAARGE MASSSSSSSSSSSSSSSSSS  altho it is very very very teeeny weeny space between the atom but it has a high masss

[WARRIOR]

RADIOACTIVITY  ( UNSTABLE ELEMENTS )

UNSTABLLE NUCLEASE BREAKS UP AND RELEASES ENRGY IN FORM OF RADIOACTIVITY

WE ARE ALL EXPOSED TO BACKGROUND RADIOACTIVITY  by radioactive materials in rocks , the air etc but this is very small so it doesnt affect us and does not produce any noticeable affects on our health!

BACKGROUND RADTIATION IS = 20 COUNT PER MINUTE  but sicne radioacttivity is  A RANDOM process it varies slightily


now we have 3 types of radiation

ALPHA PARTICLES
an alpha particle is made up of 2 protons and 2 neutrons .
It has posotive charrge  (2 + ) .
Can be stopped by few mm  paper  or a few cm of air thats why you can avoid alpha radiation by stayin 6cm away from it !
Mass 4 units ( VERY HEAVY thats why its hard to deflect towards the negative plates )
Speed  : slooooooooow caz its heavvvyyyyyyy 10% SPEED OF LIGHT
Ability to ionise : STRONG !! +4 ..OMG!!!
DEFELCTION BY ELECTRIC FIELD : DEFLECT A LITTLE TOWARDS THE NEGATIVE PLATES
DEFLECTIIN BY MAGNETIC FIELD : DEFLECT SAME DIRECTION OF WIRE ( LEFT HAND FLEM.) BUT DIFFRENT DIRECTION OF BETA
DETECTORs : PHOTOHRAPHIC FILM. CLOUD CHAMBER . THINE WINDOW G-M TUBE . SPARK COUNTER

BETA PARTICLE
Define : Fast moving electron  ( light ) emitte from the nuclease when a neturon splits up into a proton and an elctron !.
It has -ve charve ( -1)
Can be stopped by a few mm of Aluminium
MASS 1/1840 = 0
SPEED : 50% SPEED OF LIGHT  FAST OMG OMG
Abiltiy to ionise : Weak -1 nooblet
Deflection by electric field : tWARD +VE PLATE
deflection by mag """"""""" : OPPOSITE DIRECTION OF WIRE
DETECTORS : PHOTGRPAHIC GILM. CLOUD CHAMBER . G-M TUBE

GAMMA RAYS
IS A WAVE WIHT VERY VERY SHORT WAVELENGTH ( SHRTEST ) .I
LOOOOOOOOOL NO CHRGE AHAHHAHAHAH
MASS : ZEROOOOOOOO NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOBY
SPEED : SPEED OF LIGHT   WOOOOAAAH!
REMEMBER : REDUCED BUT NOT STOPPED BY LEAD!!!!!!!!!!!
Abillity to ionis : pffffffffttttt very weak as no charge..almost neglectable !
DEFLECTION BY ELEC : NO
DEFLECT BY  MAGE    : NO
DETECECTORS : PHOT FILM . CLOUD CHAMBER  . G-M TUBE

[J.Darren]

EVIDENCE FOR THE NUCLEAR MODEL

THE GOLD EXPERIMENT ( ALPHA PARTICLES ARE + )
ALPHA PARTICLES WRER FIRE THROUGH VERY THIN GOLD FOIL AND A DETECTOR WAS MOVED AROUND THE FOIL TO CHECK THE MOVEMENTS ( I.E DEFLECTION - TWISTS - ETC)

http://www.iop.org/activity/education/Teaching_Resources/Teaching%20Advanced%20Physics/Atomic%20and%20Nuclei/Images%20500/img_mid_5329.gif

this is whats happening ^ ..you see the yellow point in the middle of of the clouds,, see how small the nucleus is compared to it?

ANYWAY  YOU HAVE TO EXPLAIN WHAT IS GOING ON !

THE ALPHA PARTICLES GOING STRAIGHT WIHTOUT DEFLECTION TELLS  THAT THE ATOM IS NEARLY ALL EMPTY!! SPACE APART FROM THE NUCLEUS!  AND SO..

THE ALPHA PATICLES  THAT WERE DEFLECTED BY SMALL ANGLES SHOW US THAT THE NUCLEAS WHICH REPELLED ALPHA PARTICLS WHICH PASSED VERY VERY VERY VERY VERY CLOSE TO IT GOT REPELLED ..TELLS US THAT NUCLEUS IS POSOTIVE. AND SO

THE ALPHA PARTICLES (ABOUT 1 IN 8000 ) WERE SURPRISINGLY BOUNCED BACK !!!!!!!!!!!!!!!!> THIS TELLS US THAT THE ALPHA PATICLES COLLIDED WITH THE TINY WEENY TINY WEENY  POSITIVE NUCLEASE , SO IT TELLS US THAT IT HAS A LAAAAARGE MASSSSSSSSSSSSSSSSSS  altho it is very very very teeeny weeny space between the atom but it has a high masss

Say for instance when a beam of alpha particle is released at the gold nucleus, it gets diverged into three paths : one that shoots directly at the gold nucleus, one that goes past the gold nucleus, one that travels away from the gold nucleus.

Also if it is a beam of alpha particle, you may as well treat it as a current and use Fleming's Left-hand rule in calculating whether it is traveling away or into the paper as alpha particle is positively charged. In the case for beta particle, reverse the direction of the current.

[J.Darren]

RADIOACTIVITY  ( UNSTABLE ELEMENTS )

UNSTABLLE NUCLEASE BREAKS UP AND RELEASES ENRGY IN FORM OF RADIOACTIVITY

WE ARE ALL EXPOSED TO BACKGROUND RADIOACTIVITY  by radioactive materials in rocks , the air etc but this is very small so it doesnt affect us and does not produce any noticeable affects on our health!

BACKGROUND RADTIATION IS = 20 COUNT PER MINUTE  but sicne radioacttivity is  A RANDOM process it varies slightily


now we have 3 types of radiation

ALPHA PARTICLES
an alpha particle is made up of 2 protons and 2 neutrons .
It has posotive charrge  (2 + ) .
Can be stopped by few mm  paper  or a few cm of air thats why you can avoid alpha radiation by stayin 6cm away from it !
Mass 4 units ( VERY HEAVY thats why its hard to deflect towards the negative plates )
Speed  : slooooooooow caz its heavvvyyyyyyy 10% SPEED OF LIGHT
Ability to ionise : STRONG !! +4 ..OMG!!!
DEFELCTION BY ELECTRIC FIELD : DEFLECT A LITTLE TOWARDS THE NEGATIVE PLATES
DEFLECTIIN BY MAGNETIC FIELD : DEFLECT SAME DIRECTION OF WIRE ( LEFT HAND FLEM.) BUT DIFFRENT DIRECTION OF BETA
DETECTORs : PHOTOHRAPHIC FILM. CLOUD CHAMBER . THINE WINDOW G-M TUBE . SPARK COUNTER

BETA PARTICLE
Define : Fast moving electron  ( light ) emitte from the nuclease when a neturon splits up into a proton and an elctron !.
It has -ve charve ( -1)
Can be stopped by a few mm of Aluminium
MASS 1/1840 = 0
SPEED : 50% SPEED OF LIGHT  FAST OMG OMG
Abiltiy to ionise : Weak -1 nooblet
Deflection by electric field : tWARD +VE PLATE
deflection by mag """"""""" : OPPOSITE DIRECTION OF WIRE
DETECTORS : PHOTGRPAHIC GILM. CLOUD CHAMBER . G-M TUBE

GAMMA RAYS
IS A WAVE WIHT VERY VERY SHORT WAVELENGTH ( SHRTEST ) .I
LOOOOOOOOOL NO CHRGE AHAHHAHAHAH
MASS : ZEROOOOOOOO NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOBY
SPEED : SPEED OF LIGHT   WOOOOAAAH!
REMEMBER : REDUCED BUT NOT STOPPED BY LEAD!!!!!!!!!!!
Abillity to ionis : pffffffffttttt very weak as no charge..almost neglectable !
DEFLECTION BY ELEC : NO
DEFLECT BY  MAGE    : NO
DETECECTORS : PHOT FILM . CLOUD CHAMBER  . G-M TUBE

Those radiation is called radioactive decay. We have alpha particle decay where 2 protons and 2 neutrons (Helium) is gone from a Radium-226 nucleus, the proton number got reduced to 86, a Radon nucleus is formed. In a beta decay a neutron in Iodine-131 gets converted to a proton, forming Xenon-131 (same mass number, but an increase in the proton number), an electron and anantineutrino is released. There is another type of beta-decay where a proton gets converted into a neutron, an electron and neutrino is released.

Half-life is the time it takes for a radioactive isotope to halve its size in a decay.

Alpha particle and beta particle would ionise Argon gas inside a Geiger-Muller tube, this is due to their respective positive / negative charge.

By the way in an experiment that requires to measure the number of alpha / beta particles emitted, be sure to subtract the background reading.

[WARRIOR]

thanks darren ill write those as concluions on my topic after im done!

[WARRIOR]

IONISING AFFECTS OF RADIATION

AN ION IS AN ATOM WHICH GAINED OR LOST ELECTRONS

RADIATION CAN IONISE AIR BY KNOCKIN ELECTRONS FROM ATOM

FROM ABOVE WE KNO THE BEST ALPHA THEN BETA THEN GAMMA

SPARK COUNTER

http://www.promma.ac.th/chemistry/element_property/images/spark.gif

RADIUM IOONISES AIR . POSOTIVE IONS MOVE TO CATHODE AND NEGATIVE MOVE TO ANODE. ALPHA PARTICLES CAN BE DETECED USING  SPARK COUNTER SINCE ALPHA PARTICELS ARE EXCELLENT AT IONISING

G-M TUBE

http://williamson-labs.com/images/gmtube-273.gif

A tube that contains a high voltage inside a metal case that is earthed
WHY HIGH VOLTAGE ? TO ATTRACT THE CHARGED FROM TO ANODE ADN CATHODE

remember the g-m tube can detect radiations but CANNOT differentiate between the three types.

When radiation enters the tube it ionise the gas inside the tube adn there is flow of charge w hich prouduces a spark from the wire to the case. Th e posotive ions move to the cathode adn the negative electrons move to anode.

An ampliver connected to the tube clicks every time there is a spark


HOW TO DIFFERNTANE??
WELL YOU HAVE TO GET THE RADIOACTIVE SOURCE and put PAPER , ALUMINIUM AND LEAD BETWEEN the source adn the DETECTOR! (remember some can pass and some cant!)

remember always take BACKGROUND RADIATION FIRST! lets say its 20 !!

so example COUNTS PER MIN   ABSORBER USED
                4000                     NON
                 2700                      THIN PAPER
               20                            aluminium
this means some counnts are stopped ! that means this source produced ALPHA PARTICELS SINCE ITS STOPPED BY PAPER !
but wait !!!!!!!! counts did go to 20 ..that means there is also soem other  radioacttive stuff.. NOW WE ADD ALUMINIUM and counts dropped to 20 that means there are beta particels!!!!!!!! but count dropped to 20 and so there are no otehr radioactive  like gamma..but if there was gamma then there would still be counts!


CLOUD CHAMBER
IM NOT SURE IF ITS ON SYLLABUS SO I WONT EXPLAIN UNTIL SOME1 TELLS ME ITS ON :p







Thin window is necssary so that ALPHA PARICLES CAN ENTER G-M TUBE ( REMMBER ITS STOPPED BY PAPER !)

[WARRIOR]

SAFETY PRECATUION

KEEP ALL RADIOACTIVE IN LEAD CONTAINORS . ( LEAD STOPS ALPHA BETA AND REDUCES GAMMA)
KEEP AS FAR AWAY FROM SOURCE AND USE TONGS TO HANDLE

KEEP EXPOSURE TIME AS SHORT AS POSSIBLE

BURY WASTES DEEP IN GROUND

RADIACTIVTY BADGE
-------------------------------

RADIOACTIVE DECAY

NUCLEI OF ATOMS OF A RADIOACTIVE SUBST ARE UNSTABLE AND SOONER OR LATER THEY WIL BREAK UP OR DECAY FORMIN A MORE STABLE ONE . THIS MEANS A NEW ELEMEMTN IS FORMED . NO ONE KNOWS WHEN A NUCLEAUS WIL BREAK UP , IT IS ENTIRELY RANDOM PROCESS


ALPHA DECAY 
WHN A SUBTANCE EMITES ALPHA PARTICLES IT LOSES TWO PRTOTNS AND 2 NEUTRONS FROM ITS NUCLEUS

THE NUCLEON NUMBER IS REDUCED BY 4 AND PROTON NUMBER REDDUCED BY 2

EQUATION

A                                 A-4                          +   4
  X ---->                            Y                               a
Z                                 Z-2                                2           


BETA DECAY


RELEASE WHN A NETURON SPLITS UP INTO A PROTON AND AN ELECTRON

EQUATION

A                                     A                               0
  X --->                               Y           +                 e
Z                                  Z+ 1                             -1


Gamma decay
No affect on nucleas of an atom as it has no mass or charge !

[WARRIOR]

HALF LIFE  OF A RADIOACTIVE SOURCE

TIME TKEN FOR THE ACTIVITY OF THE SOURCE  TO HALVE

THE HALF LIFE IS TH ETIME TAKE FOR THE SOURCE TO LASE HALF ITS RADIOACTIVE ATOMS

DECAY IS RANDOM

Some isotopes have a short half -life and they decay very quick while others have a vey long adn take a long time. Value of half life is not affected by temp , presure etc.

EXAMPLE :

IODIE 131 HAS A HALF LIFE OF 8 DAYS WHEN IT DECAYS IT TURNS TO XENON 131

 IF WE START OFF WITH 80MILLION IODINE 131 , EIGHT DAYS LATER THERE WILL BE 40 MILLION IDIOEN 131. THE NUMBER OF XENON-131 NUCLEI ARE INCREASE FROM ZERO TO 40 MILLION

Another 8 days ...HALF OF 40 IS ..HMMM .. 20 !..SO 20MILLION IDONE 131 AND XENEON WILL BE 60 M ...GET THE POINT??


DECAY CURVE

TOO HARD TO EXPLAIN SO YOU SHOULD VIISIT THIS SITE

http://www.astarmathsandphysics.com/igcse_physics_notes/igcse_physics_notes_radioactivity_and_half_life.html

[WARRIOR]

USES OF RADIOACIVE ISOTOPES

TO DETECT CRACKS IN UNDERGROUND PIPES. THE RADIOACTIVE GAS LEAKS OUT THRO THE CRACK AND CAN BE DETECED THE A G-M COUNTER

TYPE OF SOURCE : BETA EMITTER CAZ IT CAN PENTERATE SOIL AND PIPES  .  ALSO USE 1 WITH SHORT HALF LIFE SO ITS RAADIOACTIVITY DOESNT CONITUE FOR LONG TIME SO IT DOESN POISON PEOPLE

why not gamma why not alpha ? ask yourself?
---------------------------

IN PAPER FACTORIES WHERE THICKNESS OF PAPER IS MEASURES BY SHOWING HOW MUCH RADIATION PASSES THRO THE PAPER. IF TOO MUCH RAD. PASSES TRHO , THEN PAPER IS TOO THIN

TYEP OF SOUURC : BETA CAZ CAN EASILY PASS TRHO PAPER AND COUNTS CAN BE DECREASSED BY THICK PAPER WITH LONG HALF LIFE SO THAT ITS ACTIVITY IS CONSTANT .DUUH U DONT WANT IT TO FINISH DO YA? DOO YAAA ??

why not gamma why not alpha ? ask yourself?

---------------------------------

EQUIPMENT IS HOSPITALS ARE STERILISED USING RADIATION

 TYPE OF SORUCE GAMMA EMITTER WITH RASONABLY SHORT HALF LIFE  S

GAMMA KILLS BACTERIA :@ :@


----------------------------------------

CHEEEEEEEEERS ATOMIC PHYS IS DONE

[Helium]

Can someone plz explaind the expression F=kx,

Its in phys syllabus i know whats hooke law but the i use says nothing about that expression.

[WARRIOR]

this is about springs


It says that force is proportiional to extension

F IS FORCE
K  IS SPRING CONSTANT X IS EXTENSION

The constant is defined as how much force is need to stretch the spring by 1m adn the unit is N/m or N/mm or N/cm

K = F/x

a spring with a large spring constant  is hard to stretch ( needs alot of force ) while one with small spring constant need less

[2010]

Thanks a lot Kimo Jesus!
That really helped!:D