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XI Chap # 01

Chapter 1 - The Scope of Physics

1. The branch of physical science, which deals with interaction of matter and energy, is called __________.
(Physics, Chemistry, Biology)
2. The new era of modern physics began near the end of __________.
(17th century, 18th century, 19th century)
3. Screw and lever were invented by __________.
(Newton, Huygen, Archimedes)
4. Pythagoras is famous in __________.
(Physics, Chemistry, None of these)
5. In the field of research the strong incentive comes from __________.
(Bible, Quran, Ingeel)
6. Number of ayah which are taken from Surah Nooh for our book are __________.
(11 and 12, 13 and 14, 15 and 16)
7. Number of ayah taken from Surah ‘Al Imran’ __________.
(170 and171, 180 and 181, 190 and 191)
8. Al-Khawarizmi was the founder of __________.
(Microbiology, Analytical Algebra, Physics)
9. Logarithm was invented by __________.
(Al- Beruni, Al-Khawarizmi, Ibn-e- Sina)
10. In Muslim world the man was both a poet and a mathematician is __________.
(Omer Khyyam, Al-Khawarizmi, Al-Beruni)
11. Kitabul Manazir was written by __________.
(Yaqoob Bin Ishaq, Ibn-e-Sina, Ibn-al-Haitham)
12. Pin hole camera was invented by __________.
(Ibn-al-Haithan, Al-Razi, Al-Beruni)
13. Ibn-e- Sina was famous for his research in the field of __________.
(Medicine, mathematics, physics)
14. Muslim scientist who wrote about 200 books is __________.
(Abn-e-Sina, Al-Razi, Omer khyyam)
15. 20th century is called the century of __________.
(Physics, Chemistry, Mathematics)
16. Dimension of acceleration is __________.
(LT-1, LT-2, L-1T)
17. The significant figures of 16, 7 are __________.
(7, 6 and 7, 1, 6 and 7)
18. The author of Kitab-ul-Masoodi was __________.
(Al-Beruni, Ibn-e-Sina, Ibn-al-Haitham)
19. The author of Al-Qanun-Fil-Tib was __________.
(Al-Beruni, Ibn-e-Sina, Ibn-al-Haitham)
20. Alsh-Shifa an encyclopedia of philosophy was written by __________.
(Al-Beruni, Ibn-e-Sina, Abn-al-Haitham)
21. Atomic clock is a (briefly) radio transmitter giving out short waves of wavelength about __________.
(3cm, 3m, 3A°)
22. The time interval occupied 9192631770 cycles of a specified energy change in the Cesium atom is taken as equal to one __________.
(second, minute, hour)
23. The ampere is the unit of __________.
(time, electric current) 

XII :Chap # 11


1.      The energy that flows from a high temperature object to a low temperature object is called __________.
(Heat, Sound Electricity, Solar Energy)
2.      Hotness or coldness of an object is expressed in tems of a quantity called __________.
(Heat, Temperature, Kelvin, None of these)
3.      The SI unit of heat is __________.
(Calorie, Joule, Electron Volt, None of these)
4.      The energy expended when a force of one Newton moves an object one metre in the direction in which the force is applied is called __________.
(Calorie, Joule, kwh, Electron Volt)
5.      1J=__________.
(1Nm, 1kgms2, 1kgm-2,1kgm2s-1)
6.      1J = __________.
(kgms, 1 kgms2, 1kgm2s-2, 1kgm2s-1)
7.      The average kinetic energy of the molecules of the object is called its __________.
(Heat, Temperature, Hotness, Coldness)
8.      __________ is a device used to measure the degree of hotness or coldness of the object.
(Thermometer, Barometer, Hypsometer, None of these)
9.      Generally thermometers make use of the fact that most of the liquids __________ on heating.
(Compress, Expand, Evaporate, Sublimize)
10.  On Celsius scale boiling point of water is taken as __________.
(0°C, 100°C, 180°C, None of these)
11.  On Celsius scale freezing point of water is taken as __________.
(0°C, 100°C, 180°, None of these)
12.  1°C = __________.
{5/9 (°F – 32), 5/9 (°F + 32), 5/9 (°F – 273), 5/9 (°F + 273)}
13.  1°F = __________.
{5/9 (°C – 32), 5/9 (°F + 32), 9/5 (°C + 32), None of these}
14.  K = __________.
(273 + °C, 273 - °C, 273 + °F, 273 - °F)
15.  1 cal = __________.
(11.184J, 2.184J, 3.184J, 4.184J)
16.  __________ proposed that matter and energy are equivalent.
(Newton, Einstein, Maxwell, All the these)
17.  The equation representing the interconversion of matter and energy is written as __________.
(E = mc, E = mc2, E = mc3, All of these)
18.  Conversion of one gram of matter to energy yields __________ joules of energy.
(9 x 1013J, 9 x 1012J, 9 x 1011J, 9 x 1010J)
19.  The amount of heat required to raise the temperature of 2.0 x 108kg of water from 0°C to 100°C is equal to __________.
(9 x 1013J, 9 x 1012J, 9 x 1011J, 9 x 1010J)
20.  During the combustion of 3 x 106 kg of coal __________ of matter is converted into energy.
(1g, 1kg, 1mg, None of these)
21.  The temperature at which the gases if they remain in gaseous state exert zero pressure and have zero volume is called __________.
(1°C, 1°F, 1K, Absolute Zero)
22.  The sum total of all the energy of all the molecules of atoms in an object is known as __________.
(Temperature, Entropy, Internal Energy, None of these)
23.  Once the heat is transferred to an object, it is converted into the __________.
(Entropy of the object, Internal energy of the object, Temperature of the object, None of these)
24.  “Temperature remaining constant the volume of given mass of a gas is inversely proportional to the pressure applied on it.” It is called __________.
(General Gas Law, Boyle’s Law, Charle’s Law, None of these)
25.  “At constant pressure the volume of a gas is proportional to the absolute temperature.” It is called __________.
((General Gas Law, Boyle’s Law, Charle’s Law, None of these)

Physics CH # 18

Review Questions

Q.1 The bohr theory of hydrogen atom is based upon many assumptions. Do any of these assumption contradict classical physics?
Ans: The assumption in bohr’s theory that an electron moving around the nucleus in a certain orbit does not radiate energy is contrary to the classical physics.

Q.2 Why does the hydrogen gas produced in laboratory not glow and emit radiations?
Ans: A spectrum is given by the light emitted from an incandescent gas or vapors. For example electric discharge through a gas or hydrogen filled discharge tube

Q.3 Why are the energy levels of the hydrogen atom less than zero?
Ans:The energy levels of hydrogen are negative. This shows that an electron must do that amount of work to escape from electron or to over come the binding energy of that orbit.

Q.4 If hydrogen gas is bombarded by electrons of energy 13.6 eV, would you expected to observe all the lines of hydrogen spectrum?
Ans:the Hydrogen will get ionized because 13.6 is the energy of ground state and is equal to the ionization energy. As such no spectral lines will observed.

Q.5 Hydrogen gas at room temperature absorbs light of wave length equal to the lines in the Lyman series but not those of Ballmer series. Explain
Ans: Hydrogen gas at room temperature contains electron in the ground state so the energy it will absorbed must be equal to the difference of energy in the first orbit and  excited state .so the radiations are related to the Lyman (n=1)

Q.6 How are X-ray different from the visible radiations?
Ans: Because They
            * Are Penetrating        *Cause ionization in Gases     * Can eject photo electrons from metals                     * Produce fluorescence  * Can damage living tissues

Q.7 What property of X-ray makes them so useful in seeing otherwise invisible internal structures?
Ans:In solids atoms are arranged in a manner. which has distance in the order of X-rays. Hence crystal is used as transmission grating to produce diffraction of X rays. This crystallography helps us to locate the internal structure.

Q.8 Explain the difference between laser light and incandescent lamp(or bulb).

Laser light
Incandescent light
 Highly monochromatic
Mixture of several wavelengths
Coherent Waves
It is not coherent
It consists of parallel waves
It is emitted in all directions
Due to stimulated emission
Due to spontaneous emission

Q.9 Name some applications of laser.
Ans: 1-Three dimensional images of objects obtained by using laser in a process called Holography.2- As a surgical tool for welding detached retina.3- To perform precesion survey and length measurements 4-As potential energy source for inducing nuclear fusion reaction.5-For telephone communication along optical fibers.6-For cutting the metals

What are the basic postulates of Bohr's Atomic Theory?

Neil Bohr studied the spectrum of hydrogen atom. On the basis of his study, he proposed a theory, which is known as Bohr's Atomic theory.


The important Postulates of Bohr's Atomic Theory are as follows:

Angular Momentum
Electrons revolve only in those orbits for which its orbital angular momentum is an integral multiple of h/2π, i.e.
L = mvr(n) = nh / 2π
m = mass of electron
V = velocity of electron
r(n) = radius of nth orbit
n = Principal quantum number
h = Plank's Constant

1. Energy
The total energy of an electron remains constant as long as it remains in the same orbit. i.e. it does not radiate energy while revolving around the nucleus.

2. Energy Release
When an electron jumps from a higher orbit having energy 'En' to a lower orbit having energy 'Ep' then energy is released in the form of energy 'hv' i.e.
Eo - Ep = hv = hc / λ
v = Frequency of Photon
λ = Wavelength of Photon
c = Speed of light
h = Plank's constant

Find out the radius, energy and wave number of hydrogen atom with the help of Bohr's Atomic theory.


A hydrogen atom is the simplest of all atoms. It consist of a proton in the nucleus and an electron revolving around the nucleus.


Consider an electron of charge '-e' revolving in a hydrogen atom around a proton of charge '+e' with constant speed v.
When the electron revolves around the nucleus, then two forces balance its motion.
Coulomb's Force = F = ke² / r² -------- (I)
Centrifugal Force = F = mv² / r ------- (II)
Comparing eq (I) and (II)
ke² / r² = mv² / r
=> ke² / mv² = r² / r
=> r = ke² / mv² -------- (III)
According to Bohr's theory, angular momentum is an integral multiple of h/2π
mvr = nh / 2π
=> v = nh / 2π mr
=> 1/v = 2π mr / nh
Taking square of both sides
=> 1/v² = 4π² m² r² / n²h²
Substituting the above value in eq (III)
r = Ke² / m = 4π² m² r² / n²h²
=> r / r² = 4π² m k e² / n²h²
=> 1 / r = 4π² m k e² / n²h²
=> r = n²h² / 4π²m k e²
We know that,
k = 1 /4π Єo => 1 / k = 4π Єo
=> r = n²h² / 4 π² m e² x 4π Єo
=> r = n²h² Єo / π e²
The above equation gives the radius of hydrogen atom.

Radii of Various Orbits
Radius of first orbit of hydrogen atom is calculated by substituting the following values in the equation of radius.
n = 1
h = 6.25 x 10(-34) J.sec
m = 9.1 x 10(-31) kg
k = 9 x 10(9) Nm²/col²
e = 1.6 x 10(-19) col
r = (1)² (6.625 x 10(-34)² / 4² (9.1 x 10(-31) (9 x 10(9)) (1.6 x 10-19)²
=> r = 0.53 x 10(-10)m
=> r1 = 0.53 Aº
For other orbits radius is given by
r2 = (2)² x 0.53 Aº
r3 = (3)² x 0.53 Aº
rn = n² x 0.53 Aº


An electron revolving in the orbit of hydrogen atom possesses kinetic energy as well as Potential Energy. Therefore, total energy is given by
E = K.E + P.E ------ (I)

Kinetic Energy
When an electron revolves in the orbit, then coulomb's force is balanced by centrifugal force
ke²/r² = mv²/r
=> mv² = ke²/r
=> 1/2 mv² = ke²/2r
=> K.E = ke²/2r

Potential Energy
Potential energy is given by
P.E = F.dr
=> P.E = Ke² / r² dr
=> P.E = ke² 1 / r² dr
=> P.E = ke² |-1/r|
=> P.E = -ke² [1/r - 1/∞]
=> P.E = -ke² (1/r - 0)
=> P.E = -ke² / r

Total Energy
Substituting the values of K.E and P.E in eq (I)
E = ke² / 2 - ke² / r
=> E = k2² / 2r
r = n² h²/ 4π² m k e²
=> E = ke² / 2 4π² m k e² / n² h²
=> |E = 2π² m k² e² / n² h²|
The above equation gives the energy of the orbits of hydrogen atom. Negative sign shows that the electron is bound with the nucleus. When energy of the electron becomes positive, then electron will leave the nucleus.

Explain the spectrum of hydrogen atom.


When an electron jumps from a higher orbit to a lower orbit, it radiates energy which appears in the form of a spectral line. A set of such spectral lines is known as hydrogen spectrum. Hydrogen spectrum is the simplest one which consists of five series.

1. Layman Series
When an electron jumps from a higher orbit to the first orbit, Laymen Series (ultra violet region) is obtained.
The wavelength and wave number of Laymen Series can be calculated by
v = R(H) (1/1² - 1/n²)
Where n = 2, 3, 4, ......

2. Balmer Series
When an electron jumps from a higher orbit to the second orbit then Balmer Series (visible region) is obtained.
The wavelength and wave number of Balmer Series can be calculated by
v = R(H) (1/2² - 1/n²)
Where n = 3, 4, 5, ......

3. Paschen Series
When an electron jumps from a higher orbit to the third orbit then Paschen Series (infra red region) is obtained.
The wavelength and wave number of Paschen Series can be calculated by
v = R(H) (1/3² - 1/n²)
Where n = 4, 5, 6, ......

4. Bracket Series
When an electron jumps from a higher orbit to the fourth orbit then Bracket Series (infra red region) is obtained.
The wavelength and wave number of Bracket Series can be calculated by
v = R(H) (1/4² - 1/n²)
Where n = 5, 6, 7, ......

5. Pfund Series
When an electron jumps from a higher orbit to the fifth orbit then Pfund Series (infra red region) is obtained.
The wavelength and wave number of Pfund Series can be calculated by
v = R(H) (1/5² - 1/n²)
Where n = 6, 7, .....

Write a note on spectra of X-rays. Also write down the properties.
X-Rays were discovered by W.K. Roentgen are also known as Roentgen rays. These rays of shorter wavelength, ranging from 0.1 nm to i nm. X-rays are produced if heavier atoms are bombarded by energetic electrons.


A Filament F and target T are produced in a vacuum chamber and voltage V is applied across the ends. Electrons are produced by heating the filament. These electrons are accelerated towards the metal by applying very high voltage (several thousands volts). When electrons hit the target, then X-rays are produced. There are two types of spectra obtained from this experiment.
1. A continuous spectrum of frequencies or X-rays Brems Strahlung.
2. Characteristics spectrum or a line spectrum of a limited number of fairly definite frequencies.

1. Continuous Spectra
When electrons hit the metal target, a continuous spectrum of frequencies of X-rays is emitted. The frequencies depend upon the accelerating voltage and are very nearly independent of the material of target.
Continuous spectrum is produced when electrons pass close to the atomic nuclei. The are deflected and slowed down due to which they lose their energy. The energy lost by decelerating electrons appears in the form of photon in the X-ray range. The process is represented as
Atoms + e(Fast) -----> Atom + e(Slow) + hv

2. Characteristic Spectra
In the heavy atoms, electrons are assumed to be arranged in concentric shells at increasing distance from the nucleus. The electrons of inner shell are much tightly bound as compared to the electrons of outer shells. Therefore, a large amount of energy is required to displace them Consequently photons of larger energy are emitted when atoms are stabilized. Thus the transition of inner shell electrons gives rise to high-energy spectra or Characteristic spectra. To obtain characteristic spectra, target metal of higher atomic number is used.
The process of emission of characteristic spectra takes place as follows. When a highly energetic incident electrons knocks an electron from the k-shell, a vacancy occurs in that shell. This vacancy is filled by the arrival of an electron from outside the k-shell, emitting excess amount of energy in the form of photon.
If the electrons jumps only one shell and returns with the emission of X-rays to Y shell, then X-rays are termed as 'Yα' X-rays. If the electron jumps two shells and returns with emission of X-rays to suppose 'Y' shell, then X-rays are termed as 'Yβ' rays and so on, where Y may be K, L, M, ......


1. X-rays are highly energetic radiation.
2. X-rays are the most shortest radiations.
3. X-rays are electromagnetic radiations that move with the speed of light.
4. X-rays have high penetrating power.
5. X-rays move in straight line and produce shadow when an obstacle is placed in front of them.
6. X-rays are not deflected by electric and magnetic fields.
7. X-rays produce ionization in gases and eject electrons from certain metals.
8. X-rays produce fluorescence in many substances.
9. X-rays being electromagnetic waves can be reflected, refracted, diffracted and polarized under suitable conditions.


1. The major use of X-rays is in medical and diagnostic treatment.
2. X-rays are used at customs and security posts.
3. The diffraction property of X-rays is used to detect arms, explosives.

Laser is a device used to produce very intense, highly directional, coherent and monochromatic beam of light.
Laser of different power and application can be produced by using different materials.
Lasers are divided into three main classes depending upon their origin.
*Solid Laser
*Liquid Laser
*Gas Laser
*There must be a meta stable state in the system.
*The system must achieve population inversion.
*The photons emitted must be confined in the system for a time to allow them further stimulated      emission.

The principle of laser production is based on the fact that atoms of a material have a number of energy levels in which at least one is meta stable state.
Consider a three level atomic system having energies E1, E2 and E3 respectively.
Let the atoms are at ground state E1. If photons interact with an atom in ground state, the atom absorbs the photon and reaches the excited state E3 . We know that the excited state is an unstable state, therefore, electron must return back to ground state E1 but such transitions are not allowed and the electron first reach the state E2. Atoms in the state E3 which has a life time of about 10-8 sec decay spontaneously from state E3 to state E2 which is meta stable and has life time of 10-3sec . This means that the atoms reach state E2 much faster than they leave state E2. This results in an increase in number of atoms in state E2, and hence population inversion is achieved.
After achieving population inversion it is exposed to a beam of photons which causes induced emission of photons and a beam of laser is produced. 

Ruby is a crystal of Al2O3, a small number of whose Al atoms are replaced by Cr+3 ions. A high intensity helical flash lamp surrounding the ruby rod is used as light source to raise Cr atoms from state E1 to E3
The ruby laser is a cylindrical rod with parallel, flat reflecting ends. One end is partially reflecting. The flash light is attached with the high voltage.
Let the electrons are raised from ground state E1 to Excited state E3 which has a life time 10-8 sec. The atoms from the state E3 make transition to state E2. Since E2 is meta-stable state having life time equal to 10-3 sec. This means that the atoms reach state E2 much faster than they leave state E2. This results in an increase in the number of atoms in state E2 and hence population inversion is achieved.
In this process few Cr atoms make spontaneous transition from E2 to E1 and emitted photons stimulate further transition. In this way we obtain an intense, coherent, monochromatic beam of red laser

Physics CH # 19

Review Questions
Q.2 Do α, β and γ rays came from the same element .Why do we find all three in many radioactive elements?
Ans: A radioactive element either emits α-particles or β-Particles ,but never both. Gamma radiations are the companion of alpha or beta. So the radioactive sample is the mixture of radioactive elements so we can have all three in many.

Q.3 It is more difficult to start a fusion reaction that fission. Why?
Ans:In fission there in no extra work done to overcome the repulsive force between two protons as in the nuclear fusion so that is why it is difficult to produce he nuclear fusion

Q.4 Is it possible that fusion of two small nuclei may occur without collision at extremely high energy?
Ans:No .Two nuclei must collide with sufficient kinetic energy to penetrate their mutual columb barrir and coming with in the range of nuclear forces.

 Q.6 What are benefits and risks of nuclear reactors? Which reactor is relatively better from the point of safety?

 Produce Electricity
Leakage of radioisotopes
Nuclear fuels
Hazards for workers
Produce radioisotopes
Damages the environment
Clean burning
Limited supply of raw materials

Q.7 Both fission and fusion apparently produce energy. How can you reconcile this with the law of conservation of energy?
Ans: In fission of U-235 with thermal neutrons, the loss of mass (0.2153u) is converted into energy producing about 200 Mev per fission
            In Fusion, four protons may be combined to produce one helium nucleus and two positrons. here the loss of mass(0.027 u)is converted into energy producing about 26Mev.Thus in both the cases the mass-energy remains conserved

Q.8 When a photon disappears in producing an electron and positron, is the energy of a photon equivalent to that of particles produced? Explain.
Ans:No,the energy of photon is always grater than the rest mass energy of electron –positron pair(1.02Mev) The remaining energy is carried by the particles as their K.E.
Q.10 Why do most moderators used in nuclear reactors are light atoms like 1H1, 1H2 or 6C12 to slow down the neutrons instead of using heavier atoms?
Ans:Fast moving neutrons can be stopped when they make elastic collision with stationary particles of the same mass. Since mass of protons, deuteron and graphite nucleus is comparable with the mass of neutrons, hence they slowed down.

Q.11 Can conventional fission reactors ever explode like a bomb does? Why?
Ans:In nuclear reactor ,a fission explosion is not possible, because the amount of fuel is of sub critical mass and it can shut off control rods in emergency. Also liquid poison can be inserted directly in to moderator if other safety devices fail.

Q.12 In a LMFBR why would you expect the radioactivity of sodium coolant to increase with the life time of the reactor.

Ans:Yes,Because sodium can captures neutrons: 11Na23+ 0n1   ----------->    11Na24 + γ
            Here Na 24 is radioactive with half life of 15H


The nucleus consists of protons and neutrons. A protonis a positively charged particle having mass 1.6726 x 10(-27) kg and charge 1.6 x 10(-19) coulomb. The charge of the proton is equal in magnitude of the charge of an electron, but opposite to it in sign. Neutrons have no charge. Its mass is 1.6750 x 10(-31). The mass of proton is 1836 times the mass of an electron.


The sum of the number of protons and neutrons in a nucleus is called Mass Number.
It is denoted by 'A'. This number is also called Nucleus Number.


The number of protons in a nucleus is called Atomic Number or proton number or charge number.
It is denoted by 'Z'.


The difference between mass number and atomic number is called Neutron Number.
It is denoted by 'N' and is given by
N = A - Z


An element X having mass number A and atomic number Z is represented by the symbol zXA.
Where X is the chemical abbreviation for the particular element.


The elements having same atomic number but different mass number or neutrons number are called isotopes.
For example hydrogen deuterium and tritium
Hydrogen A = 1, Z = 1, N = 0
Deuterium A = 2, Z = 1, N = 1
Tritium A = 3, Z = 1, N = 2

Explain the phenomenon of radioactivity.
Henri Bacqural discovered that Uranium atoms (z = 92) emit highly penetrating radiations that could penetrate paper, glass and even aluminium. On the basis of his experimental results, he explained the phenomenon of radiation.

The phenomenon of spontaneous disintegration of nucleus of atoms is known as radioactivity.

Radioactivity is a self-disrupting activity exhibited by some naturally occurring elements. It has been found, that the elements with atomic number greater than 83 are unstable and emit certain type of radiations. Such substances (e.g. Uranium, Radium, Thorium) are called Radio-active substances and the radiations emitted from their nuclei are called radio active radiations and the phenomenon is known as Radioactivity. Rutherford and his co-workers proved that the radiations emitted by a radio active substance are of three different types.

Radio Active radiations can be separated by applying electric or magnetic field to the element. A small amount of radioactive substance is placed at the bottom of a cavity drilled in a block of lead. When the narrow beam of radioactive rays is allowed to pass through the space between the two charged plates, the path of some rays bend. A similar effect is observed in the presence of magnetic field.

Results Obtained
The conclusion that were made fro the experiment are

1. α - Particles
The rays towards the negative plate indicate that they consist of positively charged particles. These were named as α-rays.

2. β - Particles
The rays bending towards the positive plate indicate that they consist of negatively charged particles. These were named as β (beta) rays.

3. γ - Rays
The rays that go undeflected indicate no charge and are therefore energetic photons or γ (gamma) rays.

Properties of α - Particles
1. α - Particles are Helium nuclei. The charge of a α-particle is twice the charge of a proton and its mass is four times than that of a-proton.
2. The speed of α-particles is 1/100 times the speed of light.
3. They produce fluorescence and effect the photographic plate.
4. α - Particles have low penetrating power.
5. They have high ionization power.
6. When a nucleus zXA disintegrates by the emission of an α-particles, its charge number (z) decreases by 2 and mass number (A) decreases by 4.
zXA ----> Z2 (VA.4) + α - Particle

Properties of β - Particles
1. β - Particles are electrons with more energy as compared to ordinary electrons because their origin is nucleus and not the atomic orbits.
2. The speed of β - particles is 1/10 times the speed of light.
3. They produce fluorescence and affect the photographic plate.
4. β - particles have greater penetrating power then α-particles.
5. They have low ionizing power.
6. When a nucleus zXA disintegrates by the emission of β - particle, its charge number (Z) decreases or increases by 1, while mass number remains same.
zXA ----> z+1 γA + -1βº (electron)
zXA ----> z-1 γA + +1βº (positron)

Properties of γ - Rays
1. γ - Rays are energetic photons and have no charge. They are similar to X - rays but more energetic.
2. They travel with the speed of light.
3. The produce fluorescence and affect the photographic plate.
4. Their penetrating power is very high.
5. They do not have any ionization power.
6. When γ - Rays emit out from the nucleus of a radio active substance, then the mass number (A) and charge number (Z) remain same
zXA ----> zXA + γ - Rays
Where zXA represents the nucleus in excited state.

Define and explain the law of radioactive decay. How can you determine the half life of a radioactive substance with the help of this law?


The rate of decay in a radioactive process is directly proportional to the number of parent nuclides, present in the unstable nuclides of the given species.

Mathematical Form
If ΔN be the number of nuclides disintegrated in time Δt and N be the number of Nuclides at time t, then:
ΔN ∞ N
ΔN ∞ Δt
=> ΔN ∞ NΔt
=> ΔN = -λNΔt
=> ΔN / Δt = -λN
Where is the decay constant and negative sign shows that number of atoms decrease w.r.t
=> 1/N ΔN = - λΔt
=> ΔN / N= - λΔt


It is the time in which half of radioactive elements decays from paront element to daughter element.
It is denoted by T 1/2.

Suppose we have 10,000 radioactive atoms. If in 10 seconds, 50,000 of them decay, then this time is called the half life that radioactivity element.

Explain nuclear fission reaction also discuss its type.

In 1943, Fermi, Serge and their co-workers studied the phenomenon of nuclear studies the phenomenon of nuclear reactions. On the basis of their experimental results they proposed a remarkable reaction. This was advanced by many scientist and fission reaction was discovered.

The process in which a heavy nucleus breaks up into two lighter nuclei of nearly equal masses after bombardment by a slow neutron is known as nuclear fission.

When an isotope of uranium of 92U235 is bombarded with slow moving neutrons, then fission reactions takes place. During this process two new elements three neutrons and a large amount of energy is released. The two nuclei of new elements produced are Barium and Krypton. The nuclear fission reaction.
Barium and Krypton are known as Fission pigments, which are radio active. A large amount of heat energy is also liberated, which may be produced.


Fission reaction is a chain reaction that has been classified into the following two types.
1. Controlled Fission Chain Reaction.
2. Uncontrolled Fission Chain Reaction.

1. Controlled Fission Chain Reaction
In a fission reaction for one atom of uranium, three neutrons are produced, which may give rise to fission reaction in other uranium atoms. If two neutrons out of three are stopped then chain reaction takes place at uniform rate and a fixed amount of energy is obtained. This is done by usually Cadmium or graphite rods. In a nuclear reactor controlled chain reaction takes place.

2. Uncontrolled Fission Chain Reaction

If in a fission reaction, the number of neutrons is not controlled, then the reaction will build up at a very fast rate and in only few seconds, an explosion occurs. In an atom bomb, uncontrolled fission chain reaction takes place.

Define and explain the phenomena of Nuclear Fusion.


A process in which two light nuclei combine (or fuse together) to form a heavy nucleus and energy is released is called Nuclear Fusion.
The energy released is called Thermo-Nucleus Fusion Energy.

For example when light nuclei of hydrogen are combined to form a heavier nucleus of helium energy is liberated. The final mass is smaller than the initial mass and the deficit of mass is comparatively greater than in fission. For this reason the energy liberated in the process of fission.
It is very difficult to produce fusion reaction due to the fact that when two positively charged nuclei are bought closer and closer and then fused together. Work has to be done against the electrostatic force of repulsion. This requires a great deal of energy.
Fusion reaction can produce great amount of energy. The raw material 1 the reaction is deuteron, which is found in abundance in world oceans as heavy water.
The fusion reaction is possible in sun and stars because of very high temperature. The fusion reactions are also the basic source of energy in stars including the sun.
This process is called Proton-Proton cycle. In this fusion process the amount of energy released is of the order of 25 MeV.
Another fusion process is suggested by Bethe. It is called Carbon-Nitrogen cycle or simply Carbon Cycle. This process is assumed to occurs in the sun. In this process four protons are converted into an alpha particle with carbon acting as a catalyst in the reaction.

Physics CH # 20

Review Questions

Q.20.1 Explain how would you test whether the radiation from a radioactive source are γ, β, α Particles?
Ans. If the radiations are allowed to pass from a magnetic field then the radiations can be identified because of the deflection the α and β particles changes their path and γ rays pass went un deflected.

Q.20.2 A particle produces more ionization is less penetrating. Why?
Ans. Due to the ionization the particle losses some part of energy. so it will have small penetrating power so we can say that the grater ionization the more will be loss of energy and less will be penetrating power..

Q.20.3 It is said that α or β Particles carries an atom with out colliding with electrons. How can each do so?
Ans. As we know tat the charge on α particle is positive while β has the negative charge. Therefore the α particle ionizes the atom by attraction and  β  particle ionizes by repulsion.

Q.20.4 In how many ways γ rays produce ionization of the atoms?
Ans. (i) It may lose only a part of energy in a collision (Compton effect)
        (ii) It may lose all energy in colliding with the electron (Photoelectric Effect) 
       (iii) It may be stopped by a heavy nucleus giving rise to the pair production

Q.20.5 In what way a neutron produces ionization of an atom?
Ans. It can ionize by colliding with a substance containing a large number of hydrogen atoms and knocks out a proton.

Q.20.6 Name different electromagnetic radiations which are capable of producing ionization of atoms. By what process do they ionize?
Ans. (i) Ultraviolet rays (ii) Gamma rays and (iii) X- rays .These rays can interact with the material in elastically and remove electron from it.

Q.20.7 Why is lead better shield against γ, β, α particles than an equal thickness of water column?
Ans. As we know that the alpha and beta particles have high ionization power so they losses more energy in water than lead so water can be used for the protection against the alpha and beta particles. But gamma rays has more penetrating power so lead (which has the more electrons than water) is used.

Q.20.8 Lead is heavier than water. Yet what is more effective shield against neutrons?
Ans. If we want to stop a neutron it must collide with the nucleus of same size. When the neutron collides with the water nucleus it stops or slows down but when it collides with the nucleus of lead it bounces back with the same speed .so Water is the better shield.

Q.20.9 In an X ray photograph bones show up very clearly while the fleshy part shows very faintly. Why?
Ans. Because the X-rays can stop by the bones but can penetrate through flesh.

Q.20.10 In a cloud chamber photograph, the path of an α –particle is thick and continuous line where that of β -particle is a thin and broken line. Why?
Ans. α –particle is more ionizing than the  β –particle so it will have a clear photograph in the chamber.

Q.20.11 Why do γ-rays not give a line-track in the cloud chamber photograph?
Ans. As gamma rays don’t produces ionization directly, But it collides with the atom and eject out the electrons or beta particle from it .This beta particle also have its own track. therefore their will be many lines.

Q.20.12 A neutron can produce little ionization. is there any sure chance of getting a cloud chamber track for it or a count in the Geiger counter?
Ans. It can ionize by colliding with a substance containing a large number of hydrogen atoms and knocks out a proton. so there will be no such track on the Wilson cloud chamber and similarly it is not detected by G.M tube.

Q.20.13 A cloud chamber track of an α -particle sometimes shows an abrupt bend accompanied by small branched track. Why?
Ans. When alpha particle collides with the nucleus, the recoil nucleus will give the abrupt change in the track.

Q.20.16 Which of the rays----α, β, or γ would you advise for the treatment of: (i) Skin cancer (ii) The cancer flesh just under the skin (iii) A cancer deep inside the skin .Give reasons.
Ans. (i) For the treatment of skin cancer we use alpha particles .B/c their penetration is small
 (ii) For the treatment of cancer flesh just under the skin we use Beta particles .B/c their penetration is Medium.
(iii) For the treatment of cancer deep inside the skin we use gamma rays. B/c their penetration is very high.

Q.20.17 Two isotopes are available one of long half life and one of shorter half life, Which isotope is advisable for the treatment of patients why?
Ans. The isotope of shorter half life must be used so if some amount remains in the body must decay quickly.

Q.20.18 Why are many artificial radioisotopes are rare in nature?
Ans. The decay of these isotopes depends on their half life .All artificial isotopes has small half life.
Q.20.19 Can radiocarbon dating be used to measure the age of stone walls of ancient civilization?
Ans. No, radiocarbon dating is not used foe the measure of the age of stone walls. It is used only for the organic remains. While for stone wall uranium must be used.

What do you know about Wilson and Cloud Chamber?


Wilson Cloud Chamber is used to observe the path of ionizing particles. It helps to examine the mechanism of ionization of various ionizing radiations and the product of their interaction with material inside the chamber.

It consist of a closed cylindrical chamber with transparent glass top "I" and a movable piston on the bottom. On the sides near the top the cylindrical is provided with a glass window for light and for the ionizing particles or radiations. The piston can be moved up or down by a lever attached to it. Before making the enclosed space above the piston arright, enough quantity of a low boiling point liquid such as water or alcohol is introduced in the space to produce its saturated vapours. A small quantity of the liquid stay on the piston.

The vapours of the liquid usually condense at its dew point but the condensation never takes place in the absence of some particles, dust particles or ions, which are essential to form the nuclei (centres) of condensation. In particle free space the saturated vapour may cool much below the dew point. Then they are called Super Saturated Vapours. Paths, additional information about the charged and uncharged nature, the magnitude of the charge, the charge to mass ration (e/m), etc of the incident particle or the particle found by their interaction with the atoms can be obtained. By this very method a number of particles have been discovered.

Explain the construction and working of Gelger Counter.
Gelger counter is a portable device which is widely used for the detaction of ionizing particles or radiations.

It consists of a hollow metal cylinder, one end of which is closed by an insulating cap. At the centre of the cap is fixed a stiff straight wire along the axis of the cylinder. A thin mica or glass disc closes the other end which also serves as all entrance window for the ionizing particles or radiations. The sealed tube usually contains a special mixture (air, argon, alcohol etc) at a low pressure of 50 to 100 millimetres of mercury. A potential difference of the order of one thousand volts is applied between the metal cylinder and difference is only slightly less than than, necessary to start a discharge between the wire and a cylinder.
When an ionizing particle enter the tube under this condition if a charged particle pass through the chamber it produces ionization along its track. The condensation of vapours takes place on ion in the form of tiny droplets of fog, which can be photographed.

1. α-Particle
An α-particle is highly ionizing the ions produced are so numerous that its trade is a thick and continuous line.

2. β-Particle
β-Particle is much less ionizing its track is therfore, a thin and broken line.

3. γ - Rays
γ - Rays are photons emitted in a widening cone of some angle. They produce ionization by photoelectric effect distributed on a wide space. Some of the photoelectrons ejected by them give tiny line tracks in directions like the β- Particles and scattered dots are produced. The γ - rays not produce well-defined line track.

Physics CH # 9

1. Machine:A machine is a device by means of which useful work can be performed conveniently and it can also transfer one form of energy into another form of energy.
2. Mechanical Advantage:The ratio between the resistance or weight to the power applied in a machine is called the mechanical advantage of that machine. It is denoted by M.A.
M.A. = Weight over-comed by Machine/ Force Applied on the Machine

3. Efficiency:The ratio between the useful work done and the work done on the machine is called efficiency.
M.A = (output/Input) * 100

4. Input:Input is the work done on the machine.
5. Output:Output is useful work done by the machine.
DefinitionLever is the simplest machine in the world. It is a rigid bar, which can be rotated about a fixed point.
Principle Of Lever
In the lever the moment P acts opposite to that of work W. It means that force F tends to rotate the lever in one direction which the weight W rotates in opposite direction. If the magnitude of these moments acting in opposite direction is equal, then the lever will be in equilibrium. It means that:
Moment of P = Moment of W

Mechanical Advantage
We know that according to Principle of Lever:
Moment of P = Moment of W
=> Force * Force Arm = Weight * Weight Arm
P * AB = W X BC
M.A = W/P = AB/BC = Weight Arm/ Force Arm

Kinds Of Lever
1. First Kind Of Lever
In the first kind of lever, the fulcrum F is in the between the effort P and Weight W.
Physical Balance         Handle of Pump           Pair of Scissors            See Saw

2. Second Kind Of Lever:
In the second kind of lever, the weight W is in between the fulcrum F and effort P.
Door    Nut Cracker     Punching Machine

3. Third Kind Of Lever:
In the third kind of lever, the effort P is in between the fulcrum F and weight W.
Human forearm           Upper and Lower Jaws in the Mouth.  A Pair of Forceps

A pulley consists of a wheel mounted on an axle that is fixed to the framework called the block. The wheel can rotate freely in the block. The groove in the circumference prevents the string from slipping.
Fixed Pulley:
If the block of the pulley is fixed then it is called a fixed pulley.
Mechanical Advantage of Fixed Pulley:
In a fixed pulley, the force P is the applied force and weight W is lifted. If we neglect the force of friction then:
Load = Effort
In the given case:
Load = W * Load Arm
Load = W * OB
Effort = P * Effort Arm
Effort = P * OA
=> W/P = OA/OB
But, OA = OB, then
M.A = W/P = OB/OB
M.A = 1

Moveable Pulley:
In this pulley, one end of the rope that is passing around the pulley is tied to a firm support and effort P is applied from its other end. The load and weight to be lifted is hung from the hook of block. In this system, the pulley can move. Such a pulley is called moveable pulley.
Mechanical Advantage of Moveable Pulley:
In an ideal system of a moveable pulley, the tension in each segment of the rope is equal to the applied effort. As two segments support the weight, the effort acting on the weight W is 2P. Therefore, according to the principle of lever:
W * Radius of the Wheel = 2P * Radius of the Wheel
=> 2P = W
The Mechanical Advantage is given by:
M.A = W/P
M.A = 2P/P
=> M.A = 2
Hence, the mechanical advantage of a moveable pulley is 2.

Inclined Plane:
  Any smooth plane surface which makes an angle q with the horizontal surface is called an “Inclined plane”.
Where 0o α q α90o or values of q lies between 0o and 90o .

Uses OfInclined Plane:
It is a simple machine and is used to raise heavy loads by applying little effort.

Mechanical AdvantageOf Inclined Plane:
  In the figure AB is an inclined plane which makes an angle q with the horizontal plane. A load ‘W’ is being raised from A to B by applying an effort ‘P’. If we neglect the force of friction between load and inclined plane
Output = input
x height = effort x distance
W x h = P x L
W*h/P = L
W/P = L/h
W/P = 1/h/L
in right angled DOAB
Sin θ = OB/AB
Sin θ = h/L
[ perpendicular/hypotenuse = sin θ]
W/P = 1/sin θ
but [W/P = M.A.]
M.A. = 1/sin θ

This expression shows that mechanical advantage of an inclined plane depends upon the value of sin θ
Wheel And Axle:
    It is a simple machine and is used to lift heavy loads. It has a wheel of larger radius (R) and an axle of smaller radius (r) fixed on the same shaft. Wheel and axle are free to rotate about its shaft.

Mechanical Advantage Of Wheel And Axle:
  The effort is applied to the rim of the wheel and the load is raised by a rope wound around the axle. In one rotation wheel covers a distance of 2pR In one rotation load is raised by a distance of 2pr If we neglect force of friction,
Output = input
W x 2pr = P x 2pR
W/P = 2pR/2pr
W/P = R/r
Since [W/P = M.A.]
M.A. = R/r
M.A. = radius of wheel / radius of axle
This expression indicates that in order to increase the mechanical advantage
Radius of :wheel must have a large value and Radius of axle must be smaller than that of wheel.
Screw is one of the most important machines. It is used to hold different parts of machines together. It has waste applications in our daily life plus in industries. It is used in every type of device.

Construction And Working:
It simply consists of a threaded rod with a head known as “Screw head”. It has a number of threads. The perpendicular distance between two adjacent threads is known as pitch of screw. The thread of screw can be regarded as a continuous inclined plane wrapped round a cylinder of radius d .

Mechanical Advantage:
If we apply an effort ‘P’ on the head of screw then it turns one revolution and at the same time the screw moves forward in to the wood or wall through a distance equal to its pitch “h”. The effort ‘P’ moves through a distance 2pd. The screw remains in the wood due to frictional forces between the screw and the wood. A large amount of energy changes in to heat energy during the process of screwing.
Let us assume an ideal case when there is no loss of energy then;in this condition
Output = input
P x
2pd = W x h
W/P =
2 p d/h
Hence, the mechanical advantage of the screw will be.
M.A. = 2pd/h

The mechanical advantage of the screw depends upon the following factors.
In order to increase mechanical advantage of screw we must use a screw of small pitch.
Larger is the radius of screw head , greater is the mechanical advantage.

Screw Jack:
A screw jack is a simple machine. It is used to lift cars or heavy automobiles. It consists of a long screw rod which passes through a threaded block B and a handle . The distance between two consecutive thread is known as pitch of screw.

Mechanical Advantage:
When an effort is applied to the handle , the effort moves in a circle of radius “d” while “d” is the length of the rod and the block “B” moves up equal to the pitch of the screw jack. If the handle is turned through one complete revolution in a circle of radius “d” the effort moves through a distance 2pd and consequently the load is raised through a height h. Hence, the mechanical advantage is given by:
M.A. = 2pd/h
M.A. = Distance through which the effort is moved/height through which the load is raised
We know that the pitch of the screw is very small as compared to the length of the rod, so the mechanical advantage should be very large. Due to frictional force between the different parts of screw jack, the efficiency is less than one. It is due to the reason that a lot heat energy is used for over coming the frictional forces.
It should be remembered that in case of screw jack friction is a necessary part of operation, because in the absence of friction, it would unwind at once when applied force is removed.

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