CHAPTER SIX
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(1) ELECTRONIC ORBITS AND ENERGY LEVELS
Q) What are valence electrons?
They are the electrons which revolve in the outer shells farthest from the nucleus has
greater energy and bound to nucleus with minimum attractive force This means that
valence electrons are the ones that participate in chemical reactions and determine
electronic properties of matter.
Q) What are valence electrons advantageous?
1) revolve in the outer shells farthest from the Nucleus
2) has greater energy, and bound to nucleus with minimum attractive force
3) that valence electrons are the ones that participate in chemical reactions and
determine electronic properties of matter.
Q) What is the least amount of energy an electron in a hydrogen atom can possess? And
how much does this electron need to be liberated from the atom?
The lowest amount of energy that an electron can have in hydrogen atom is (-13.6eV), this
means when this electron gains (+13.6eV) energy, it escapes from the hydrogen atom
The conductor: - it is a material that allows flow of electric current through it, electric
charges move freely in conductors like (copper, silver, gold and aluminum). Conductors
have one valence electron very weakly bound to the nucleus. These electrons are easily
escape from the nucleus and becomes free moving (free electrons).
The Insulators: - it is a material that do not allow electric current to flow through it in normal
conditions. Valence electrons of insulators are strongly bound to the nucleus.
The Semiconductors: - material, that electric charges move less freely than conductors. The
specific electrical resistance of semiconductors ranges between that of the specific
resistance of conductors and insulators in electric conductivity,
Ministerial Exams:
Q.1) What will happen: if an electron in a hydrogen atom gains energy of magnitude
(+13.6 ev)?
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(2) ENERGY BANDS IN SOLID MATERIALS
Q) What are energy bands? What are its types?
Energy Bands: It is a group of energy levels that overlap with each other, and it is of two
types:
1) Valence Band: It is a contains low energy levels, partially or completely full of electrons
and cannot be empty. Its electrons are called valence electrons, they cannot move
among neighboring atoms because they are so close to the nucleus and bound to the
nucleus with relatively large forces.
2) Conduction Band: it is a contains high energy levels, Its electrons are called conduction
electrons, these conduction electrons can move freely to participate in electric
conduction.
Q) What is a forbidden energy gap?
Forbidden energy gap: It is a neither has allowed energy levels (nor it allowed electrons to
occupied it). Each electron must gain energy form outer source in order to move from
valence band to conduction band through forbidden energy gap. This outer energy
source (thermal, light or effect of an electric field), this amount must be not less than the
amount of forbidden energy gap.
Q) What are the advantages of energy bands in Conductor's materials?
1. Valence bands overlap with conduction bands.
2. No forbidden energy gap between valence bands and conduction bands.
Consequently, valence electrons are free to move through conductors, thus, these metals
have high electrical conductivity.
3. Electrical conductivity of metal decreases when their temperature increases due to
increase in their electrical resistance (due to increase time rate of vibrational energy of
atoms and molecules).
Q) What are the advantages of energy bands in insulators materials?
1. Valence band is full of valence electrons.
2. Conduction band is empty of electrons.
3. Forbidden energy gap is relatively wide.
Q) What are the advantages of energy bands in semiconductors?
1. Valence band are full of valence electrons.
2. Conduction band is empty of electrons.
3. Forbidden energy gap is narrow relative to insulators.
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Q) Electrical conductivity of metal decreases when their temperature increases?
Because to increase in their electrical resistance (due to increase time rate of vibrational
energy of atoms and molecules).
Q) Why the insulator has no electrical conductivity?
because the forbidden energy gap in the insulator is relatively wide (around 5eV) or more,
electrons in valence band cannot pass forbidden energy gap and move to conduction
band when the supplied energy is less than forbidden energy gap. As a result, valence
band remains full of valence electrons while conduction band is empty of electrons.
Q) What is the effect of placing a huge electric field or heat onto the insulator?
might lead to collapse of the insulator and flow of a very little current through insulator.
Ministerial Exams:
Q.1) Why the insulating material does not have an electrical conductivity?
Q.2) Why do metals have such high electrical conductivity?
Q.3) What are the characteristics of energy bands in insulating materials?
Q.4) What are the characteristics of energy bands in insulating, conducting, and
semiconducting materials?
Q.5) Why the conductivity of conductive materials decreases (metals) as their temperature
increases?
Q.6) What would happen if a large electric field was applied to the insulating material, or it
was subjected to a great thermal effect?
(3) INTRINSIC SEMICONDUCTORS
Q) How can make intrinsic semiconductor (like silicon) have electric conductivity by
thermal effect?
To answer this question, when the temperature of the intrinsic semiconductor increases to
room temperature (300K), valence electrons gain sufficient energy to break some of
covalent bonds from the source of (thermal energy) that enables
When these electrons move from valence to conduction band, each moving electron
leaves behind an empty space in valence band, this spot is called (hole) which acts as a
positive charge. At this point, free electrons generated in conduction band and equal
numbers of holes in valence band, and with this process is generated the so-called
electron-hole pair.
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Q) Time rate of generating (electron-hole) pairs in intrinsic semiconductor depends on:
1. Temperature of semiconductor.
2. Type of semiconductor material.
Q) What is the effect of the high temperature of the intrinsic semiconductor on each of the
following?
1) Forbidden Energy Gap.
2) Electron-hole pair rate.
3) Semiconductor resistivity.
4) Conductivity.
1) When the temperature increases, the amount of the forbidden energy gap decreases.
2) When the temperature increases, the rate of generation of an (electron-hole) pair
increases.
3) When the temperature increases, the resistivity of the semiconductor decreases.
4) When the temperature increases, the conductivity increases.
Q) What are the conditions that make a semiconductor material behave like an insulating
material?
1) At very low temperatures [at zero degrees Kelvin (0K)].
2) When there is no light.
3) If it is intrinsic and not tainted.
Q) effect of an electric field on the sides of intrinsic semiconductor crystal like silicon at
room temperature (300K). and answer the following:
• Does the electric current flow through the intrinsic semiconductor (Si)?
• If yes, then what is the type of this current?
When an electric field is imposed on the sides of intrinsic silicon crystal at room
temperature, free electrons are attracted easily to the positive side. As a result of free
electron movement in the intrinsic semiconductor material it creates a current is called
electron current. Another current is created in valence band, it is called holes current, the
direction of positive holes inside the crystal is toward the direction of the electric field
while the electrons move in the opposite direction of the electric field applied, this means
that holes move in the opposite direction of the electrons
Q) What is the magnitude of the forbidden energy gap of the following intrinsic
semiconductors at zero kelvin and at degree of (300K)?
1) Germanium.
2) Silicon.
At zero kelvin for silicon (1.2 ev) and germanium (0.78 ev), and at temperature (300K) for
silicon (1.1 ev) and germanium (0.72 ev).
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Q) What is the Fermi level? Where is it located in conductors and semiconductors at zero
kelvin (room temperature)?
Fermi Level: It is the highest allowed energy level that an electron can occupy at absolute
zero (0K).
In conductors, at zero Kelvin, Fermi level is lies above the region which full of electrons in
conduction band. The energy level occupied by these electrons is below Fermi level.
The Fermi level in the intrinsic semiconductors, lies in the middle of the forbidden energy
gap between conduction band and valence band.
Ministerial Exams:
Q.1) Can an intrinsic semiconductor (for example, Silicon) be made to have electrical
conductivity by means of the thermal effect?
Q.2) Under what conditions do semiconductors behave as insulators? What are the
advantages of energy bands in these conditions?
Q.3) What is the effect of high temperature on the electrical conductivity of conductors and
semiconductors?
Q.4) Do metals have high electrical conductivity? Explain this.
Q.5) Where is the Fermi level located at zero K in (conductors and semiconductors)?
Q.6) What is the effect of high temperature on the electrical conductivity of the intrinsic
semiconductor materials?
Q.7) What is meant by the Fermi level, and what is its location in the transportation and in
the intrinsic semiconductor?
Q.8) What determines the occupancy of electrons at a certain level of permissible energy
levels of the electrons? What is meant by it?
Q.9) What does the (electron-hole) pair rate depend on in the intrinsic semiconductor?
Q.10) What effect of increasing temperature of the intrinsic semiconductor on the
magnitude of the forbidden energy gap?
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(4) EXTRINSIC SEMICONDUCTORS
Q) What is meant by doping?
it is a process adding atoms of pentavalent or trivalent elements called impurities. Impurities
are added carefully and accurately (with rate of one to 108 approximately) at room
temperature and at very low rates in an intrinsic semiconductor crystal.
Q) Why we resort to doping the semiconductor with pentavalent or trivalent elements...
instead of the thermal effect? The reasons for that.
Q) Why is the doping method preferred over the semiconductor thermal method to
increase its electrical conductivity?
This is because the controlling electrical conductivity of the intrinsic semiconductor is not
possible by thermal effect method
Q) What are the methods to increase the electrical conductivity of a semiconductor?
1) Thermal effect.
2) Doping.
Q) What is the (N-type) semiconductor?
It is a semiconductor like silicon or germanium doped with a pentavalent impurity like
(antimony), so the impure atom is bound to four atoms of the semiconductor by covalent
bonds, and one electron remains free, so the resulting material is filled with electrons.
Q) What is donor atom?
It is a pentavalent impurity that has been transformed into a semiconducting substance by
doping, causing an increase in the concentration of free electrons in the conduction band,
so it becomes a positive ion and does not participate in the electrical conduction process
because it is strongly bind to the crystal structure.
Q) Donor atom (positive ion) does not participate in the electrical conduction process in
the doped semiconductor. Why?
Because the positive ion is strongly bind to the crystal structure.
Q) What is meant by the donor level?
A level occupied by electrons released by the donor atoms. It is generated when
pentavalent impurities are added to a semiconductor crystal, and it falls within the
forbidden energy gap and under the conduction band, and as a result, the Fermi level rises
and approaches the conduction band.
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Q) Why is the concentration of electrons in the conduction band greater than the holes
concentration in the valence band in the (N-type) semiconductor type?
Because electrons liberated by pentavalent impurities do not leave holes in the valence
band when moving to the conduction band.
Q) Why are electrons called primary (majority) charge carriers and holes called secondary
(minority) charge carriers in the (N-type) semiconductor?
Electrons are called primary charge carriers because they are generated from the doping
and thermal effect processes. The holes are called secondary charge carriers because
they are only generated by the thermal effect.
Q) Why is a semiconductor crystal after its doping with a pentavalent impurity called (Ntype) semiconductors (i.e., negative crystal)?
Because the majority charge carriers are negative electrons, and the minority charge
carriers are the positive holes.
Q) What is the net charge magnitude of the (N-type) crystal? And why?
Its magnitude is zero. Because the number of negative charges is equal to the number of
positive charges.
Q) What is the (P-type) semiconductor?
It is a semiconductor like silicon with a trivalent impurity like (boron), so the impure atom is
bound to three atoms of the semiconductor by covalent bonds, leaving one atom of the
semiconductor that lacks one electron, leaving a positive hole and the voltage of the
resulting material is positive.
Q) What is acceptor atom?
It is an atom of a trivalent impurity (such as boron) that accepts an electron from the
valence electrons in order to bind with four electrons of silicon by covalent bonds, so the
impurity becomes a negative ion that does not participate in the electrical conduction.
Q) Why does the acceptor atom (the negative ion) not participate in the electrical
conduction process in the extrinsic semiconductor?
Because the negative ion (the acceptor atom) has a strong bond with the crystal structure
(with the crystal atoms).
Q) What is meant by the acceptor level?
It is an energy level that located within the forbidden energy gap and directly above the
valence band and is generated when a trivalent impurity is added to the semiconductor
crystal, and as a result, the Fermi level decreases and approaches the valence band.
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Q) Why is the concentration of the holes in the valence band greater than the
concentration of electrons in the conduction band?
Because the trivalent impurity atom causes a gap in the valence beam when it accepts
an electron from the valence electrons.
Q) Why are the holes called the primary (majority) charge carriers and electrons as the
secondary (minority) charge carriers in the (P-type) semiconductor type?
The holes are called the primary charge carriers because they are generated by the
doping and thermal effect processes. Electrons are called secondary charge carriers
because they are only generated by the thermal effect.
Q) Why the semiconductor crystal called a semiconductor crystal after its doping with a
trivalent (P-type) semiconductor impurity (i.e. the positive crystal)?
Because the primary charge carriers are, the positive holes and the secondary charge
carriers are the negative electrons.
Q) What is the net charge of the (P-type) crystal? And why?
Its magnitude is zero. Because the number of positive charges equals the number of
negative charges.
Ministerial Exams:
Q.1) Why the positive ion generated when adding a donor-type impurity to an intrinsic
semiconductor crystal is not considered as a charge carrier?
Q.2) What is meant by the donor level?
Q.3) Is there a hole in the silicon of (N-type).
Q.4) What happens to a Fermi level site when an intrinsic semiconductor is doped with a
pentavalent impurity?
Q.5) Why the semiconductor crystal after its doping with a pentavalent semiconductor
impurity called (N-type) semiconductor and sometimes the negative crystal? Is this
crystal charge negative?
Q.6) What happens to a Fermi level site when an intrinsic semiconductor is doped by
adding impurities?
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(5) PN DIODE
Q) What is the PN Diode?
It is a silicon crystal with one side doped with trivalent impurities (boron), so we get a
semiconductor part (P-type) and the other side doped with pentavalent impurities
(antimony), so we get a semiconductor part (N-type). The surface separating the two areas
is called the junction, and the two ends of the contact are coated with a metallic
substance that the wires connected to at the PN diode can be connected to the outer
circuit.
Q) What is the Depletion region in the crystalline diode (PN)?
It is a thin region on both sides of the junction that contains positive ions in the region (N)
and negative ions in the region (P) and is devoid of charge carriers.
Q) How is the Depletion region generated in a crystalline diode (PN)?
the free electrons in (N) region close the (PN) junction spread (osmosis) to (PN) region,
generating positive ions in (N) region, holes move from (P) region to (N) region through
the junction, generating negative ions in (P) region. Then, electrons combine with holes
near the junction.
This process causes a thin region on the two sides of the junction containing positive ions in
(N) region and negative ions in (P) region, and is devoid of charge carriers, this region is
called Depletion region.
Q) When does the Electrons spread through the (PN) junction stops? What is the explanation
for that?
Electrons spread through the (PN) junction stops when there is an equilibrium state.
What is the explanation for this?
The continuous electrons spread through (PN) junction generate more positive ions and
negative ions on both sides of the (PN) junction at depletion region. This creates an electric
field (represented by red arrows), the electric potential difference resulting from this filed
prevents additional electrons from passing the (PN) junction, so, electrons stop spreading
process, this is called potential barrier.
Q) What is the potential barrier in a crystalline diode? And on what is it based?
It is the electric potential difference resulting from the electric field generated by the
positive and negative ions in the Depletion region. It depends on:
1) the type of semiconductor.
2) rate of doped impurities.
3) temperature of the material.
Q) What is the practical benefit of the crystalline diode?
to control direction of the current or to change or to improve output signals shape,
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Ministerial Exams:
Q.1) What is the practical benefit of the crystalline diode?
Q.6) What does electric barrier potential magnitude in the crystalline diode depends on.
Chapter Six Questions
Q.1) Choose the correct answer:
3. Free electrons in intrinsic semiconductor at room temperature occupy:
a. Valence band.
b. Forbidden energy gap.
c. Conduction band
d. Acceptor level.
4. Electron-hole pairs are generated in intrinsic semiconductor by:
a. Recombination.
b. Ionization.
c. Doping.
d. Thermal effect.
5. Flowing current in intrinsic semiconductor is the result of:
a. Free electrons only.
b. Holes only.
c. Negative ions.
d. Both electrons and holes.
6. In (N-type) semiconductor and at room temperature:
a. Number of free electrons in conduction band equals number of holes in valence band.
b. Number of free electrons in conduction band is greater than number of holes in
valence band.
c. Number of free electrons in conduction band is less than number of holes in valence
band.
d. All of the above, depending on type of impurity.
7. Depletion region is generated in (PN-diode) by:
a. Recombination.
b. osmosis.
c. ionization.
d. All previous possibilities (a, b and c)
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11. Silicon acts as insulator when:
a. Pure.
b- In the dark.
c. At absolute zero.
d. All of the three choices (a, b, c).
12- Time rate for generating electron-hole pair increases in semiconductor by:
a- Adding pentavalent impurities
b- Adding trivalent impurities
b- Increase in temperature
d- None of the above
17. In semiconductor N-type and at (0K), Fermi level lies at:
a. Below donor level.
b. Middle distance between bottom of conduction band and donor level.
c. In the middle of energy gap.
d. Middle distance between valence band and donor level.
18. Fermi level is:
a. Average of all energy levels.
b. Energy level at the top valence band.
c. Higher energy level occupied at (0o) C.
d. Higher energy level occupied at 0K.
Q.2) Write True or false, correct the false without changing underlined:
1. (N-type) silicon crystal has negative charge.
Answer / False - (Type N) Silicon crystal has a neutral charge.
2. Depletion region in PN-diode contains positive ions in P region and negative ions in N
region.
Answer / False - Depletion region in PN-diode contains negative ions in P region and
positive ions in N region.
3. Electric conductivity in intrinsic semiconductor increases when temperature rises.
Answer / True
5. Forbidden energy gap in germanium is (1.1eV) at (300K).
Answer / False - Forbidden energy gap in germanium is (0.72 eV) at (300K).
8. In conductors at 0K the energy levels below Fermi level are occupied by electrons.
Answer / True
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10. Electron-hole pairs are generated in semiconductor because of recombination
between electrons and holes.
Answer / False - Electron-hole pairs are generated in semiconductor because of electron
movement from valence band to conduction band.
14. P-Type germanium crystal, the holes are the majority charge carriers.
Answer / True
Q.3) What is the difference between the following:
1- Positive ions and positive hole in semiconductors.
Positive Ion
Positive hole
It consists of a pentavalent donor impurity
atom such as Antimony that has lost its fifth
electron.
It is an electron-free site that originate from
the extraction of one electron from the
Silicon or Germanium atom as a result of a
thermal effect, or it originate from the
removal of one electron from the Silicon or
Germanium atom as a result of doping the
semiconductor material with a contiguous
impurity.
It bonds with four contiguous silicon.
Therefore, the impure atom becomes a
positive ion.
It is not considered a charge carrier
because it does not participate in the
electrical conduction of the recombinant
semiconductor because it is closely
related to the crystal structure.
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Be free to move
It has a role in electrical conductivity and is
the primary carriers in the semiconducting
material of P-type and secondary in the
semiconductor material of N-type
3- N-type semi-conductor and p-type semi-conductor in terms of:
a- Type of doped impurity,
b- Majority charge carriers and minority charge carriers.
c- Level and position generated by each impurity.
N-type Semiconductor
P-type Semiconductor
Impurities of pentavalent atoms (for
example, Antimony).
Impurities of trivalent atoms (for example,
boron).
Electrons in the conduction band.
Positive holes in the valence band.
Positive holes.
Free electrons.
The donor level is within the forbidden
energy gap and directly below the
The acceptor level falls within the
conduction band. The donor level is
forbidden energy gap and directly above
occupied by electrons, which released by
the valence band and as a result, the
the donor atoms and as a result, the Fermi Fermi level decreases and approaches the
level rises and approaches the conduction
valence band.
band.
Q.4) Explain the reasons of the followings:
a. Generating of depletion region in PN crystalline diode?
the free electrons in (N) region close the (PN) junction spread (osmosis) to (PN) region,
generating positive ions in (N) region, holes move from (P) region to (N) region through
the junction, generating negative ions in (P) region. Then, electrons combine with holes
near the junction.
This process causes a thin region on the two sides of the junction containing positive ions in
(N) region and negative ions in (P) region, and is devoid of charge carriers, this region is
called Depletion region.
c. At absolute zero and in the dark, the conduction band in intrinsic semiconductor is
empty of electrons?
At a temperature of zero kelvin (T=0K) it is characterized by complete heat loss, as the
intrinsic semiconductor in the dark has no thermal or light effect, so the valence band is
filled with electrons and the conduction band is free of free electrons (intrinsic
semiconductor behaves like an insulator).
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f. The positive ion, which is generated when a donor impurity is added to intrinsic
semiconductor, is not a charge carrier?
Because this positive ion bonds with four neighboring atoms and is closely related to the
crystal structure, it does not move.
Q.5) Define the followings:
a- Fermi level.
Fermi level: It is the highest energy level that an electron can occupy at a temperature of
zero kelvin (0K).
b- Donor level and how it generates.
Donor level: A level occupied by electrons released by the donor atoms. It is generated
when pentavalent impurities are added to a semiconductor crystal, and it falls within the
forbidden energy gap and under the conduction band, and as a result, the Fermi level rises
and approaches the conduction band.
c- Depletion region in PN-diode, and how it generates.
Depletion region in PN-diode: a thin region on both sides of the junction that contains
positive ions in the N-region and negative ions in the P-region and is devoid of charge
carriers.
It is generated: because the free electrons in the N-region near the junction spread to the
P-region through the junction, and then the electrons fuse with the holes near the junction.
So positive ions are generated in the N-region and negative ions in the P-region.
d- Hole in semi-conductor, and how it generates.
Hole: a location devoid of electrons that behaves like a positive charge having the amount
of an electron charge.
It is generated: from the extraction of one electron from a silicon or germanium atom as a
result of a thermal effect or a light effect, or it is generated from the extraction of one
electron from the silicon or germanium atom as a result of doping the semiconductor
material with acceptor impurity.
e- The (electron-hole) pair and how it generates.
(Electron – hole) Pair: it is a free electron in the conduction band and an empty space in
the valence band. This space, which is called the hole, is produced as a result of the
electron transfer from the valence band to the conduction band.
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Q.6) What does the amount of the followings depend on?
a. Potential barrier in PN-diode crystalline.
1) the type of semiconductor.
2) rate of doped impurities.
3) temperature of the material.
b. The rate of creating electron-hole pair in an intrinsic semiconductor?
1) The temperature of the semiconductor.
2) The type of semiconductor material.
c. Number of free electrons moving from valence band to conduction band in n-type
semiconductor at constant temperature.
The proportion of donor atoms doped into the crystal.
Q.8) After doping a semiconductor (like silicon) by trivalent impurities (like Boron), what is
the resultant crystal. Does it have positive charge? or negative? or electrically neutral?
We obtain a P-type semiconductor crystal, the majority of charge carriers are the positive
holes, and the charge of the crystal will be electrically neutral because it has a number of
positive charges equal to the number of negative charges.
Ministerial Exams:
Q.1) After doping a semiconductor crystal (such as silicon) with trivalent impurities (such as
boron), what kind of crystal will we get? Will its charge be positive, negative, or
electrically neutral?
Q.2) Why the intrinsic semiconductor behaves like an insulator at very low temperatures
(near zero kelvin) and the absence of light?
Q.5) Why at the temperature of absolute zero and in the dark, the conduction band in an
intrinsic semiconductor is devoid of electrons?
Q.7) What does the time rate of (electron-hole) pairs generation depend on in an intrinsic
semiconductor?
Q.10) What is meant by the forward Fermi level?
Q.11) What the cause of the depletion zone formation in the crystalline PN diode?
Q.12) What the dielectric voltage magnitude in the crystal diode depends on.
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Q.13) What is the difference between the (N-type) semiconductor and the (P-type)
semiconductor type in terms of the type of impurity used in it?
Q.14) Distinguish between the positive ion and the hole in the semiconductor. (Mention only
two points).
Q.15) What does the number of free electrons transferred to the conduction band in (Ntype) semiconductor crystal depend on at constant temperature?
Q.16) What is meant by 1- the Fermi level. 2- The electron-hole pairs?
Q.17) What is meant by the donor level? and how is it generated?
Q.18) What is meant by a semiconductor hole, and how is it generated?
Q.20) Choose the correct answer: When increasing the voltage barrier in a forward biased
crystal diode; the amount of forward current in its circuit (increases, decreases,
remains constant, increases and decreases).
Q.21) Choose the correct answer: The free electrons in an intrinsic semiconductor at room
temperature equips (valence band, conduction band, acceptor level, forbidden
energy gap).
Q.23) Choose the correct answer: the current flowing in the intrinsic semiconductor is
caused by (free electrons only, holes only, negative ions, both electrons and holes).
Q.24) Put the mark (true) or (false) then correct the mistake: the (N-type) of silicon, crystal
is negatively charged.
Q.25) Choose the correct answer: The Fermi level is: [the average value of all energy levels,
the highest occupied energy level at (0K), the highest occupied energy level at (0K),
and the energy level at the top of the valence band].
Q.26) Choose the correct answer: the electron-hole pairs are generated in the intrinsic
semiconductor by (re-docking, ionization, doping, thermal effect).
Q.27) Choose the correct answer: the Fermi level is in the (P-type) semiconductor at a
temperature (0K): (below the donor level, below the acceptor level, midway between
both valence band top and the acceptor level, midway between the conduction
band bottom and the donor level).
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Q.28) Choose the correct answer: The depletion zone in the PN diode is generated by:
1) Re-docking
2) Osmosis
3) Ionization
4) All of the above
Q.29) Choose the correct answer: Silicon behaves like insulators when it is (intrinsic, in the
dark, at absolute zero, all previous answers).
Q.35) Put the mark (true) or (false) then correct the mistake: the magnitude of the forbidden
energy gap in germanium (1.1 ev).
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CHAPTER SEVEN
ATOMIC SPECTRUM AND LASER
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(1) ATOMIC MODELS
Q) What is the proposed made by the scientist Rutherford in developing the model of the
atom?
He assumed that the atom is a positive nucleus at the center of the atom with electrons
Q) Why did Rutherford's model fail?
1. When electrons revolve around the nucleus in the atom, it always changes its direction
therefore, it is an accelerated particle. According to classical electromagnetic theory,
any charge moving with certain acceleration emits electromagnetic radiation, so, the
electron moving around the nucleus must lose some of its energy while circling, i.e. it is
losing energy continuously as long as it is moving. Then, it ends in a spiral movement
approaching the nucleus in a short time, and then the atomic structure collapses,
2. When electron energy decreases gradually, a continuous spectrum is generated, while
experiments show that Hydrogen atom spectrum is line spectrum.
Q) Why have most spectroscopic studies focused on the hydrogen atom?
Because the hydrogen atom is the simplest atom in structure (consisting of one proton and
one electron).
Q) What is Bohr proposed a model of the atomic structure.?
1. Negative-charge electrons revolve around nucleus in a certain allowed orbits
representing energy levels without radiating energy, an electron has lowest energy if it is
in closer level to the nucleus, then, the atom is stable. An electron must have proper
energy and momentum to remain at this level.
2. The atom is electrically neutral when the charge of the electrons equals the positive
charge of nucleus.
3. The atom does not radiate energy because of electron revolving in stationary orbits,
and the atom is stable.
4. When an electron gains energy, it jumps from its stability level (Ei) into higher energy level
(Ef), then the atom is excited and it moves back to its stability when the electron goes
back to stability level, emitting photons with frequency (f).it is expressed as follows:
𝒉𝒇 = 𝑬𝒇 − 𝑬𝒊
𝑊ℎ𝑒𝑟𝑒
𝒉: 𝑃𝑙𝑎𝑛𝑐𝑘 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 = (6.63 × 10!"# 𝐽. 𝑠),
𝒇: 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦
5. Coulomb's law of electric charges and Newton’s second law of mechanics are applied
in atomic structure.
20 | P a g e
6. An electron has angular momentum (L= mvr) in its stationary orbit that equals integers
from (h/2π)
𝑳𝒏 = 𝒏 (
𝒉
+
𝟐𝝅
𝑊ℎ𝑒𝑟𝑒 (𝑛 = 1, 2, 3, . . . ) 𝑎𝑛𝑑 𝑖𝑡 𝑟𝑒𝑝𝑟𝑒𝑠𝑒𝑛𝑡𝑠 𝑝𝑟𝑖𝑛𝑐𝑖𝑝𝑎𝑙 𝑞𝑢𝑎𝑛𝑡𝑢𝑚.
𝒉
𝒎𝒗𝒏 𝒓𝒏 = 𝒏 ( +
𝟐𝝅
Q) Mention series of the hydrogen atom spectrum?
1) Lyman series: It is emitted when the electron of a hydrogen atom moves from the highenergy levels to the first energy level 𝑬𝟏 … … (𝒏 = 𝟏) and its frequency range lies in the
ultraviolet region (𝒖. 𝒗), it is an invisible series.
2) Balmer series: It is emitted when the electron of a hydrogen atom moves from the highenergy levels to the second energy level 𝑬𝟐 … … (𝒏 = 𝟐), and its frequency range lies in
the visible region and extends to the ultraviolet region.
3) Paschen series: It is emitted when the electron moves from the high-energy levels to the
third energy level 𝑬𝟑 … … (𝒏 = 𝟑), and its frequency range lies in the infrared region, which
is an invisible series.
4) Brackett series: It is emitted when the electron moves from the high-energy levels to the
fourth energy level 𝑬𝟒 … … (𝒏 = 𝟒), and its frequency range lies in the infrared region,
which is an invisible series.
5) Pfund series: It is emitted when an electron moves from the high-energy levels to the fifth
energy level 𝑬𝟓 … … (𝒏 = 𝟓), and its frequency range lies in the infrared region, which is an
invisible series.
Ministerial Exams:
Q.1) Mention series of the hydrogen atom spectrum?
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(2) SPECTRA
Q) What is the spectrum? What are its benefits?
Spectrum: The series of light frequencies resulting from the white light when analyzed by a
prism
Benefits: discovery of atomic and molecular structure, by analyzing light emitting from
these matters and their spectra using the spectroscope.
Q) Mention The most light sources used in studying spectra?
1) Thermal sources: which are sources that radiate light as a result of them of increasing
temperature like sun, Tungsten lamps and electrical arches.
2) 2. Sources which depend on electrical discharge through in gases, like electrical
discharge tubes at low pressure.
Q) What does the type of spectrum resulting from the analysis of radiation emitted from
gases depends on?
It depends on the type of gas.
Q) Mention the types of spectra, with clarification of each spectrum.
A) Emission Spectra:
they are spectra of incandescent materials, which are:
1) Continuous Spectrum: this spectrum is obtained from incandescent solid and liquid
incandescent material or incandescent gas under high pressure. illustrates a continuous
spectrum with a wide range of frequencies. such as the white tungsten capillary lamp, it
consists of a wide range of a continuous wavelengths within visible range.
2) Linear Spectrum: this spectrum is obtained from incandescent gases and vapors under
normal or low pressure, which illustrates a set of bright colorful lines on a black
background, each of which represents particular wavelength. , such as The bright line
spectrum of Sodium and the linear spectrum of hydrogen,
3) Band Spectrum: it is a spectrum, which contains a band or a number of bands on a black
background. Each band consists of convergent lines; it is a characteristic feature of
molecular structure materials. It can be obtained from glowing molecular materials like
Carbon dioxide gas in a discharge tube, which contains Barium salts, or Calcium salts that
are glowing by Carbonic arch.
B) Absorption Spectra:
it is a continuous spectrum punctuated by lines or dark bands. When light passes through
non-incandescent vapor (or permeable material) it absorbs from the continuous spectrum
wavelengths it emits if it was incandescent. Then we get the absorption spectrum
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Q) Compare between:
1) Linear Spectrum and Band Spectrum.
2) Continuous Spectrum and Absorption Spectrum.
Bright Linear Spectrum
Bright Bands Spectrum
It has a bunch of bright colored lines on a
black floor.
One or several colored packages contain
a black background.
A characteristic of non-combining atoms.
We get it from fumes and glowing gases
under normal pressure or less.
Distinctive feature of molecular structure
materials.
It is obtained from incandescent materials
with molecular structure as an
incandescent gas in the vacuum tube.
Continuous Spectrum
Linear Absorption Spectrum
It has a wide range of continuous and
gradient wavelengths.
A continuous spectrum with dark lines.
We get it from glowing solids, glowing
liquids, or glowing gases under very great
pressure.
We obtain it by passing the light emitted
from a source of its spectrum continuous
through gases whose atoms are not
coherent with others and are not
incandescent.
Q) What are the sodium bright linear spectrum and hydrogen linear spectrum consist of?
The bright line spectrum of Sodium consists of two bright yellow lines very close to each
other, at the yellow region of the visible spectrum.
As for line spectrum of hydrogen, it consists of four bright lines (red, green, dark blue and
purple).
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Q) Explain an activity (experiment) to demonstrate the types of spectra.
Q) Explain an activity (experiment) that demonstrates the difference in the type of spectrum
according to the type of gas.
Activity Tools:
• Glass Prism.
• Source of electrical current.
• Electric capillary lamp.
• Barrier with a split to obtain the parallel light falls on the prism
• Electric screen.
• discharge tubes (like neon, hydrogen, or mercury vapor),
Activity Steps:
1) The hydrogen tube is connected to the electric circuit to glow.
2) The glass prism is placed in the path of the light emitting band from the hydrogen gas
tube. Then change the position and incident angle of the emitted beam to obtain the
best spectrum on the screen.
3) We note shape and color of spectrum on the screen.
4) Repeat the previous steps using other gas tubes, electric capillary lamp.
5) We note the shape and color of the different spectra on the screen.
Conclusion:
We conclude that spectrum resulting from analyzing radiations emitting from other gases
differ according to the type of gas.
Q) What are the benefits of studying spectra?
detection of an unknown element in a certain material or the components of alloys.
Q) How can the components of an alloy be known by the spectra?
This can be done taking a sample of that material and vaporize it in a carbon arch to make
it glow, then its line spectrum is recorded by the spectroscope and compared with
standard spectra of each element.
Q) What are Fraunhofer lines?
black lines in the continuous spectrum of the sun, called Fraunhofer lines, named after the
scientist Fraunhofer who discovered about (600) lines of it.
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Q) What is the reason for the appearance of black streaks in the sun? Why did the
Fraunhofer lines appear?
The reason behind the black lines in the sun is that the gases around the sun and in the
atmosphere of the earth that are less glowing than the gases of the interior of the sun
absorb from the continuous spectrum of the sun the wavelengths that these gases emit if
they were incandescent,
Ministerial Exams:
Q.1) What are Fraunhofer lines? What is the reason for its appearance?
Q.2) What is meant by (bright band spectrum)? And how can it be obtained?
Q.3) What does the continuous spectrum consist of? How can it be obtained?
Q.4) What are the linear fluorescent spectrum of sodium and hydrogen linear consist of?
Q.5) Mention the types of spectra.
Q.6) What is meant by (absorption spectrum)? And how do we get it?
Q.7) Compare the continuous spectrum and the linear spectrum in terms of how to obtain
them.
Q.8) What is happen? Why? When is the vapor of a non-glowing gas intercepted and the
light emitted from a source of its continuous spectrum is transmitted?
Q.9) Why does the appearance of black streaks occur in the continuous spectrum of the
sun?
Q.10) What are the linear fluorescent spectrum of sodium and hydrogen linear consist of?
Q.11) What is the spectrum of the hydrogen atom?
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(3) X RAY
Q) What are X-rays?
X-rays are invisible electromagnetic waves with a very short wavelength. They are not
affected by electric or magnetic fields because they are not charged particles.
Q) How can an x-ray be generated?
The X-ray can be obtained by using a vacuum glass tube, this tube has two poles, one is
negative (Cathode); a filament which emits electrons when heated. The other pole is
positive (Anode); it is a metal target, which inclines by a certain angle toward the
movement of accelerated electrons. This collision causes high heat; therefore, the anode
target is made of a material of high melting point like Tungsten and Molybdenum. It is also
made of a material of large atomic number to increase efficiency of X-ray. Some
techniques are used to cool down the anode due to high heat.
Q) Why is the anode target is made of a material of high melting point like Tungsten and
Molybdenum. in the X-ray generating tube
Due to the generation of high heat as a result of collision of the accelerated electrons with
the metal target.
Q) Why is the metal target made of a material of large atomic number. in the X-ray
generating tube
to increase efficiency of X-ray.
Q) Why are Some techniques used in the x-ray tube of the target material (anode)?
To cool the target as a result of high heat generation due to the collision of the accelerated
electrons with the target atoms.
Q) Why is the X-ray is a reverse of photoelectric effect?
because it is generated to transform energy of accelerated electrons emitting from
cathode and falling on the target into X-ray photons.
Q) What does the intensity of X-rays depend on?
It depends on the number of emitted photons at a given wavelength .
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Q) Mention types of x-ray spectra. With explanation of each spectrum.
1) A sharp line spectrum X-ray: also called (Characteristic X-ray spectrum) :
electrons are fall on the atom of the target material, these electrons extract one of the
electrons from inner levels of the target material and leave the atom permanently and
ionization state occurs. This electron might go up into a higher energy level, and
becomes excited. In both cases, the atom becomes anxiety (excited) and attempts to
return to stability. When an electron falls from a high-energy level (with high energy) to
the energy level from which the electron was extracted, energy is emitted in the form of
an X-ray photons. Its energy is the energy difference between levels E1, E2 that is:
𝒉𝒇 = 𝑬𝟐 − 𝑬𝟏
This spectrum is a characteristic feature of target atom material.
2) Continuous spectrum X-ray:
This spectrum results from the collision of accelerated electrons with the atom of target
material. This collision slows down their movement because of the electric field nuclei of
target material. Because of this slowdown, electrons lose their energy and appear as X-ray
photons with different frequencies.
Q) What does the maximum frequency of the x-ray photon depend on?
It depends on the potential difference (𝑉) applied at the sides of X-ray tube
𝑲𝑬𝒎𝒂𝒙 = 𝒆𝑽
𝑲𝑬𝒎𝒂𝒙 = 𝒉𝒇
𝑊ℎ𝑒𝑟𝑒 𝑲𝑬𝒎𝒂𝒙 : 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑚𝑎𝑥𝑖𝑚𝑢𝑚 𝑘𝑖𝑛𝑒𝑡𝑖𝑐 𝑒𝑛𝑒𝑟𝑔𝑦, 𝒆: 𝑒𝑙𝑒𝑐𝑡𝑟𝑜𝑛 𝑐ℎ𝑎𝑟𝑔𝑒,
𝑽: 𝑝𝑜𝑡𝑒𝑛𝑡𝑖𝑎𝑙 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒, 𝒉: 𝑃𝑙𝑎𝑛𝑐𝑘 , 𝑠 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡, 𝑓: 𝑝ℎ𝑜𝑡𝑜𝑛 𝑓𝑟𝑒𝑞𝑢𝑒𝑛𝑐𝑦
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Q) Derive the mathematical formula for the shortest wavelength of X-ray photons.
Q) Derive the mathematical formula for the highest frequency and shortest wavelength of
the X-ray photons.
𝒉.𝒄
Q) Derive the following relationship(𝝀𝒎𝒊𝒏 =
).
𝒆.𝑽
Answer:
𝑲𝑬𝒎𝒂𝒙 = 𝑽𝒆
𝑲𝑬𝒎𝒂𝒙 = 𝒉𝒇𝒎𝒂𝒙
∴ 𝒉𝒇𝒎𝒂𝒙 = 𝑽𝒆
𝒇𝒎𝒂𝒙 =
𝒄
𝑽𝒆
𝒉
=
𝑽𝒆
𝒉
𝝀𝒎𝒊𝒏 =
𝒉𝒄
𝑽𝒆
𝝀𝒎𝒊𝒏
Q) What are the applications of X-rays?
1) Medical field:
It used in radiography, detection of tooth decay, specify location shrapnel and bullets in
the body, as well as detection and treatment of some tumors in the body. X-ray is also used
to sterile medical equipment
2) Industrial field:
it is used to detect dents and cracks in metal molds and wood used in building boats.
Studies on absorption spectrum helped in making X-ray one of the ways of detecting and
analyzing component elements of various materials. It is also used in study of solids and
crystalline structures.
3) Security field:
X-ray is used in checking passengers’ luggage in airports,
It is also used in identifying the methods of painters and distinguishing between real
paintings and fake paintings,
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Q) How to use X-ray in identifying the methods of painters and distinguishing between real
paintings and fake paintings?
By passing x-rays on the paintings, where the colors used in old paintings contain many
metallic compounds, which absorb X-ray while modern paintings are organic compounds,
which absorb less X-ray.
Ministerial Exams:
Q.1) How the x-rays are used to identify the styles of painters and distinguish between real
and fake paintings?
Q.2) Why is a metal target in an x-ray tube made of tungsten?
Q.3) What does the intensity of X-rays depend on?
Q.4) How is it possible to detect the presence of an unknown element in a substance or to
know the components of an alloy by spectroscopic methods?
Q.5) Can x-rays be affected by electric and magnetic fields?
Q.6) Why is X-ray a reversible photoelectric phenomenon?
Q.7) Why in the generation of x-rays the target made of a substance with a very high
melting point and a large atomic number?
Q.8) What does the highest frequency of the X-ray photon depend on?
Q.9) How is the sharp linear spectrum produced in x-rays?
Q.10) How is it possible to detect the presence of an unknown element in a substance or to
know the components of an alloy by spectroscopic methods?
Q.11) Compare between the real paintings and the fake paintings of painters by using Xrays.
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(4) COMPTON EFFECT
Q) Explain the Compton phenomenon (Compton Effect)?
when a band of X-rays (photons) of a given wavelength (λ) is incident on a target metal of
pure graphite, rays will scatter with different angles. Scattered ray has a longer wavelength
(λ') than that of the original ray (λ) for the incident ray. Change in wavelength (λ' -λ)
increases with the increase in scattering angle (θ) and an electron emit on the other side
of the target,
𝝀) − 𝝀 =
𝒉
(𝟏 − 𝒄𝒐𝒔𝜽)
𝒎𝒆 𝒄
Q) What is the text of the Compton phenomenon (the Compton effect)?
Increase in wavelength of scattered X-ray photons by free electrons of target atom,
compared to wavelength of incident photons depends on scattering angle (θ) only
according to the following relation:
𝝀) − 𝝀 =
𝒉
(𝟏 − 𝒄𝒐𝒔𝜽)
𝒎𝒆 𝒄
Q) What is Compton's explanation for the increase in the wavelength of a scattered X-ray
photon?
the incident photon on graphite target collides with a free electron from the target
material, losing some of its energy. After collision, this electron gains an amount of kinetic
energy, enabling it to travel and leave target material (The photon acts as particles).
As a result, the energy of the photon decreases, its frequency decreases and its
wavelength increases.
Q) In Compton effect, what does the magnitude of the increase in the wavelength of a
scattered X-ray photon depend on?
It depends on the angle of scattering (θ), and as in the relationship:
𝝀) − 𝝀 =
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𝒉
(𝟏 − 𝒄𝒐𝒔𝜽)
𝒎𝒆 𝒄
Q) Does the Compton Effect confirm the particle behavior or wave behavior of
electromagnetic waves? Why?
Compton Effect is an important proof particle
The reason: Because the incident photon on graphite target
collides with a free electron from the target material, losing some of its energy.
Q) Why is the collision between a photon and a free electron in the Compton Effect of the
elastic type?
the collision between the photon and the free electron is elastic scattering, because it
follows laws of momentum conservation and energy conservation.
Q) What does the Compton wavelength represent?
Compton wavelength:
𝒉
= 𝟎. 𝟐𝟒 × 𝟏𝟎+𝟏𝟏 𝒎
𝒎𝒆 𝒄
Ministerial Exams:
Q.1) What factors determine the amount of increase in wavelength of X-ray photons
scattered by free electrons of target atoms?
Q.2) What is Compton's explanation for the increase in the wavelength of an X-ray photon
scattered by free electrons on a graphite target?
Q.3) Mention the text of the Compton Effect mentioning its mathematical relationship?
Q.4) What is meant by the Compton Effect?
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(5) LASER AND MASER
Q) What are the origins of LASER and MASER names?
The name (laser) came from the first letters of the idea of laser work, which are:
Light Amplification by Stimulated Emission of Radiation
The name (mazer) came from the first letters of the idea of maser work, which are:
Microwave Amplification by Stimulated Emission of Radiation
Q) What are the characteristics (advantages) of laser beam?
1) Monochromatic Wavelength (monochromaticity)
2) Coherency.
3) Directionality.
4) Brightness.
Q) Compare laser beams with regular light rays.
LASER BEAM
LIGHT REGULAR RAYS
Monochromatic Wavelength
Polychromatic Wavelength
Coherent: all waves have the same phase
and direction and have the same energy.
Directionality: It has little detente and
parallel beam.
Brightness: It has a very high brightness
intensity.
(A million times brighter than a regular
beam of light).
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Incoherent: the waves have different
phases, in different directions, and with
different energy.
Different directions: It has different detente
and it scattered.
Brightness: It has a low brightness intensity.
Chapter Eight Questions
Q.1) Choose the correct statement:
1. Bohr’s model of atom shows that:
a. Gaseous elements have identical atomic spectra.
b. Glowing solid elements have identical atomic spectra.
c. Glowing liquid elements have identical atomic spectra.
d. Each element has its own atomic spectrum.
2. When an atom is excited by a continuous radioacting energy then the atom:
a. Absorbs all radioacting energy.
b. Absorbs the suitable energy to excite its atoms.
c. Absorbs energy continuously.
d. None of the above.
3. We get Lyman series in hydrogen spectrum when:
a. The electron of hydrogen atom transmitted from (E5, E4, E3, E2) energy levels to first
energy level.
b. The electron of hydrogen atom transmitted from (E5, E4, E3, E2) energy levels to second
energy level.
c. The electron of hydrogen atom transmitted from high energy levels to third energy
level.
5. A hydrogen atom spectrum is:
a. Continuous.
b. Line absorption.
c. Line.
d. Band.
6. Increase in wavelength of scattered X-ray photons by free electrons depend on:
a. The wavelength of incident photon.
b. Speed of light.
c. Electron mass.
d. Scattering angle.
e. Type of metal.
10. Measuring range using laser depends on one of its properties which:
a. Coherency.
b. Polarization
c. Monochromatic wavelength.
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d. Directionality.
Q.2) Give the reason of the following:
1. Wavelengths in absorption spectrum of an element is exist in emission spectrum
also.
When light passes through non-incandescent vapor (or permeable material) it absorbs
from the continuous spectrum wavelengths it emits if it was incandescent. Then we get
the absorption spectrum
2. Compton Effect is one of the evidence of particle behavior of electromagnetic ray.
because the incident photon on graphite target collides with a free electron from the
target material, losing some of its energy. After collision, this electron gains an amount of
kinetic energy, enabling it to travel and leave target material (The photon acts as
particles).
3. In producing X-ray, target material is made of high-melting point material.
Due to the generation of high heat as a result of collision of the accelerated electrons
with the metal target.
Q.5) What are properties of laser beam?
1) Monochromatic Wavelength (monochromaticity)
2) Coherency.
3) Directionality.
4) Brightness.
Ministerial Exams:
Q.1) What kind of spectrum is a hydrogen atom?
Q.3) Choose the correct answer: The spectrum of the hydrogen atom is (continuous, linear
absorption, linear emission, beam).
Q.5) Choose the correct answer: The spectrum of the hydrogen atom is a spectrum
(continuous, linear absorption, linear emission, beam).
Q.6) Put the mark (true) or (false) and then correct the error: The process of measuring range
using laser beams depends on one of its properties, which is the coherency.
Q.7) Choose the correct answer: When an atom is affected by a continuous radiation
energy, the atom: (absorbs all the radiation energy, absorbs energy continuously,
absorbs the energy appropriate to excite its atoms, not one of them).
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Q.9) Choose the correct answer: The process of measuring the range using laser beams
depends on one of its properties, which is: (coherency, polarization, monochrome
wavelength, directivity).
Q.10) Why is the Compton effect one of the evidence that confirms the particle behavior of
electromagnetic radiation?
Q.11) Why would the target be made from a material whose melting point is so high in xray production?
Q.12) Why are wavelengths in the absorption spectrum of an element also present in its
emission spectrum?
Q.13) Why are wavelengths in the absorption spectrum of an element also present in its
emission spectrum?
Q.14) What are the advantages (properties) of the laser beam?
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CHAPTER NINE
ATOMIC SPECTRUM AND LASER
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(1) RELATIVITY THEORY
Q) What is meant by frame of reference? What is meant by inertial frames of reference?
Frame of Reference: It is the location in which a person monitors an event at a certain
time.
Inertial Frames of Reference : are those frames that move at a constant speed relative to
each other.
Q) How is an event observed in space according to relativity theory?
Q) How is the observation of a space event determined?
is done by identifying its position and time using four coordinates (x, y, z, t). (x, y, z) are
position coordinates, and (t) it is time coordinate,
Q) What did the relativity theory add to the classical concepts?
Accurately observing an event in space is done by determining the location and time of
the event using four coordinates, which are (X, Y, Z & t) where (X, Y, Z) are the coordinates
of the location and (t) is the time coordinate, instead of three coordinates as in classical
physics.
Q) What are Einstein's hypotheses in the special theory of relativity?
Q) What are the two hypotheses on which the relativity theory relied?
1) Laws of physics must be the same in all inertial frames of reference.
2) Speed of light in vacuum is constant (𝑪 = 𝟑 × 𝟏𝟎𝟖 𝒎/𝒔) in all inertial frames of references
regardless of observer's velocity or speed of light source.
Q) What is the conclusion of scientists Michelson and Morley in 1887?
the speed of light is constant when moves in all directions, since there is no ether
Ether: is an invisible hypothetical medium thought to exist in space. It is thought of as the
medium in which light travels
Q) What are the prerequisites for Galileo transformations that classical physics relied on
for frameworks?
Parallel axes.
Time is constant in all inertial referance frames
Velocity of referance frame S' is constant
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Q) What are Lorentz transformations and what is meant by Lorentz's parameter?
Lorentz proved, by studying movement of physical particles in electromagnetic field, that
velocity of particles has a significant effect in measuring physical dimensions of the
object. He also proved that there is a correction factor must be adopted relation to
coordinates of frames of reference (S, S'). The correction factor is called Lorentz factor (γ)
and expressed by:
ɣ=
𝟏
𝟐
A𝟏 − 𝒗𝟐
𝒄
Chapter Nine Questions
Q.1) Choose the correct phrase for each of the following:
1. Which of the following quantities is constant according to relativity theory:
a. Speed of light.
b. Time.
c. Mass.
d. Length.
2. A spaceship with a velocity (0.9c) (0.9 of speed of light) sends a light beam, the relative
velocity of this beam, which is observed by the crew of another spaceship parallel
traveling to the first spaceship and in the same direction.
a. 0.9c.
b. 1.8c.
c 1.6c.
d. c.
4. According to Einstein's theory of special relativity, all laws of physics are one in the frames
of measurement whose velocity:
a. Uniform acceleration.
b. Uniform and constant.
c. non-uniform and oscillating.
d. Rotational.
10. If you were in a rocket moving with velocity of (0.7c) towards a star, what is the velocity
will get you to the light of that star:
a. Less than c.
b. Greater than c.
c. At speed of light in vacuum.
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Q3 What is the main difference between Galilean transformations and relativity
transformations?
The main difference is the amount (ɣ =
𝟏
𝟐
,𝟏+𝒗𝟐
) and its effect on the magnitudes of the
𝒄
body's momentum, the length of the body, the mass of the body, and the measured time.
The name (ɣ) Lorentz's coefficient
Q.4) Some would say matter can neither be created nor destroyed, do you think this is true?
No, as energy can be transformed into matter or matter into energy.
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CHAPTER TEN
NUCLEAR PHYSICS
(1) MASS ENERGY EQUIVALENCE
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Q) What is the importance of nuclear physics?
The nucleus is a storehouse of energy. This nuclear energy is used for peaceful purposes
(as in transforming nuclear energy to electric energy), or for non- peaceful purposes (as in
nuclear weapons production).
Q) What was the first radioactivity discovered in history? And who is the scientist that
discovered it?
French Scientist Henry Becquerel discovered natural radioactivity in Uranium compounds.
Q) What is the nucleus model that has been developed by scientists (just note)?
1) The nucleus consists of two types of particles: the positive protons (+P) and the neutral
neutrons (N) and the charge of the neutron is equal to zero.
2) Each of the protons (P) or a neutron (N) is called a nucleus or a nucleon.
3) The number of protons in the nucleus is called the atomic number (Z) and it is equal to
the number of electrons.
4) The number of neutrons is denoted by the symbol (N) and it is called the neutron number.
5) The number of nucleons (the sum of the protons and the neutrons) called the mass
number (A). It will be (A=N+Z)
6) Chemical symbol for nucleus structure ( /.𝑋).
7) The proton is denoted by the symbol (𝑃 or 00𝐻 or 00𝑃) denotes that the proton is its atomic
number (1) and the mass number (1). The neutron is denoted by the symbol (𝑛 or 01𝑛)
indicating that the neutron has an atomic number of zero and a mass number (1).
Q) What is the symbol for the aluminum nucleus ( 𝟐𝟕
𝟏𝟑𝑨𝒍). What is the atomic number, the
neutron number, and the mass number of the aluminum nucleus?
𝑍 = 13
𝐴 = 27
𝐴 = 𝑁 + 𝑍
27 = 𝑁 + 13
𝑁 = 27 − 13
𝑁 = 14
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Q) What are isotopes?
They are nuclei that are equal in atomic number and differ in mass number such as:
( 3"𝐿𝑖 , 4"𝐿𝑖 , 5"𝐿𝑖 ) That is, they are equal in the number of protons (P) and different in the number
of neutrons (N).
Q) How much is the mass of the nucleus in comparison to the atom, and in what unit is it
measured?
The mass of the nucleus represents (99.9%) of atom mass, and it is measured by accurate
devices like mass spectrometer. Masses of atom nucleus are measured by atomic mass
unit (amu) or symboliced by (u) instead of kilogram, which is not appropriate to measure
atomic and tiny nuclear masses that equal: 𝟏 𝒂𝒎𝒖 = 𝟏 𝒖 = 𝟏. 𝟔𝟔 × 𝟏𝟎!𝟐𝟕 𝑲𝒈
Q) How is nucleus mass measured theoretically (mathematically)?
Since the nucleus contains the (A) nucleons, and Nucleon mass is close to mass of (1u),
then approximate mass of nucleus is (m') which equals (A×u).
𝒎’ = 𝑨 𝒙 𝒂𝒎𝒖
Where 1 amu = 1.66 × 10!64 Kg
Q) On what basis is the nucleus described as being heavy, medium, or light?
It is described according to mass number (or mass) whether big, medium or small
Q) Calculate the energy in units (electron - volts) equivalent to the unit of atomic masses
(u).
The value of (u) in Kg measure equal 1.66 x 10-27 Kg
𝑬 = 𝒎𝒄𝟐
𝑬 = 𝟏. 𝟔𝟔 × 𝟏𝟎!𝟐𝟕 × (𝟑 × 𝟏𝟎𝟖 )𝟐
𝑬 = 𝟏𝟒. 𝟗 × 𝟏𝟎!𝟏𝟏 𝑱
𝟏 𝒆𝒗 = 𝟏. 𝟔 × 𝟏𝟎!𝟏𝟗 𝑱
𝟏𝟒. 𝟗 × 𝟏𝟎!𝟏𝟏
𝑬=
= 𝟗𝟑𝟏 × 𝟏𝟎𝟔 𝒆𝒗
𝟏. 𝟔 × 𝟏𝟎!𝟏𝟗
𝑬 = 𝟗𝟑𝟏 𝑴𝒆𝒗
On this basis, it was found that:
and speed of light:
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𝟏(𝐮) = 𝟗𝟑𝟏 𝑴𝒆𝒗
𝒄𝟐 = 𝟗𝟑𝟏
𝑴 𝒆𝒗
𝒖
Q) How can we find the nucleus charge?
Since neutron charge is zero, the nucleus charge equals total of proton charges. So, the
nucleus of any atom is positive and its amount of charge (q) equals (+Ze)
𝒒 = 𝒁. 𝒆
𝑊ℎ𝑒𝑟𝑒
𝒁: 𝑎𝑡𝑜𝑚𝑖𝑐 𝑛𝑢𝑚𝑏𝑒𝑟,
𝒒: 𝑝𝑟𝑜𝑡𝑜𝑛 𝑐ℎ𝑎𝑟𝑔𝑒 (1.6 × 10!0> )
Q) What is the first experiment conducted to measure the size and radius of the nucleus?
With writing the mathematical equation.
first attempt to estimate volume of nucleus and radius was done by Rutherford by alpha
particle scattering of gold atom nuclei and similar experiments, that most nuclei atoms
are spherical (in this chapter, we will assume that the shape is spherical). He discovered
that nucleus radius (R) is directly proportional to cubic root of mass number (A). given by
the following relationship:
𝟏
𝑹 ∝ 𝑨𝟑
𝟏
𝑹 = 𝒓𝟎 𝑨𝟑
𝑊ℎ𝑒𝑟𝑒
𝒓𝟎 : 𝑟𝑒𝑑𝑖𝑢𝑠 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 𝑎𝑛𝑑 𝑒𝑞𝑢𝑎𝑙𝑠 (1.2 × 10!0@ 𝑚) 𝑜𝑟 (1.2 𝐹𝑒𝑟𝑚𝑖)
the Volume of nucleus (V) can be found by applying the following relation:
𝑽=
𝟒
𝝅𝑹𝟑
𝟑
𝑽=
𝟒 𝟑
𝝅𝒓 𝑨
𝟑 𝟎
Q) what is the amount of nucleus density? and what is amount of nucleus density compared
to water density?
𝑲𝒈
The density of the nucleus is equal to (𝟐. 𝟑 × 𝟏𝟎𝟏𝟕 𝒎𝟑 )
And compared to water density (𝟏𝟎𝟑
times the density of water.
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𝑲𝒈
), the nucleus density is around (
𝒎𝟑
𝟐. 𝟑 × 𝟏𝟎𝟏𝟒 )
(2) NUCLEAR BINDING ENERGY
Q) What is meant by nuclear force? And what it is the properties?
Nuclear force: it is nuclear attraction force that binds the nucleons of the nucleus, the
strongest in nature, it is short-range and does not depend on charge
properties:
1) It is a force of attraction.
2) It does not depend on the type of nucleon; it may arise between (P.P) or (P.n) or (n.n).
3) Its magnitude is large, and it is the strongest in nature.
4) it is maintaining stability and bondage the nucleus.
5) It has a short range.
Q) What is the reason: the nucleus contains positively charged protons. Why do these
protons not repulse despite similar charges?
this is because a nuclear attraction force that binds the nucleons of the nucleus. the
nuclear force is the strongest in nature. From the properties of nuclear force is does not
depend on charge.
Q) What is meant by the Nuclear Binding Energy (Eb)?
It is the energy required to disassemble the nucleus into protons and neutrons.
Q) What is meant by mass defect?
Mass of nucleus does not equal its component protons and neutrons when separated its
always less than the sum of the individual masses of protons and neutrons, this difference in
mass (Δm) is called mass defect, and it is equivalent to nuclear binding energy (Eb)
according to Einstein’s (mass-energy) equivalence relation:
𝑬𝒃 = ∆𝒎𝒄𝟐
Q) Why is the mass of the nucleus not equal to the sum of the masses of its components of
protons and neutrons when they are separated?
Q) Why the mass of the nucleus is always less than the mass of its components (protons +
neutrons) when they are separated?
This difference in mass is called mass defect (Δm), which has been found to be equivalent
to nuclear binding energy (Eb) according to Einstein’s (mass-energy) equivalence relation:
𝑬𝒃 = ∆𝒎𝒄𝟐
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/
Q) What is meant by the average nuclear binding energy (𝑬𝒃 )?
it is the Quotient of nuclear binding energy (Eb) by mass number (A), and expressed as
follows:
𝑬𝒃
𝑨
/
Q) How the average nuclear binding energy (𝑬𝒃 ) value change when the mass number of
/
𝑬𝒃 =
nuclei changes (A)?
/
The adjacent figure shows the change of (𝑬𝒃 )
with (A). It is noted from this figure that:
1) the curve is generally constant except for light
nuclei like Deuteron ( 𝟐𝟏𝑯) and heavy nuclei
like lead nuclei ( 𝟐𝟎𝟖
𝟖𝟐𝑷𝒃).
2) It also shows that medium nuclei have
/
the larger values of (𝑬𝒃 ) like Iron nucleus ( 𝟓𝟔
𝟐𝟔𝑭𝒆) thus,
medium nuclei are usually the most stable.
3) Light and heavy nuclei can be more stable if a nuclear reaction can change them into
medium nuclei.
4) heavy nuclei become more stable if fission to medium nuclei and vice versa, if light nuclei
fused to form heavier nuclei, they become more stable too. In both cases, energy will
be released.
Q) medium nuclei like iron are usually the most stable, why?
Because the medium nuclei have the larger values of average nuclear binding energy
/
(𝐸E ), therefore, they need more energy to dismantle them.
Q) How can light and heavy nuclei become more stable?
heavy nuclei become more stable if fission to medium nuclei and vice versa, if light nuclei
fused to form heavier nuclei, they become more stable too. In both cases, energy will be
released.
Q) What are the ways to obtain nuclear energy?
1) Through nuclear fusion.
2) Through nuclear fission.
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Chapter Ten Questions
Q.1) Choose the right statement for the following:
1- The radius of nucleus (R) IS change:
a) Directly proportional with A1/3
b) Inversely proportional with A1/3
c) Directly proportional with A3
d) Inversely proportional with A3
2- The amount of average nuclear binding energy per nucleon is:
a) Greater for the nucleus of the light elements
b) Greater for the nucleus of heavy elements
c) Equal to all nucleus of elements
d) Greater for the nucleus of intermediate elements
3- The followings are properties of nuclear forces except one:
a) Binds and holds nucleon of the nucleus.
b) Does not depend on the charge
c) Has very long range
d) The strongest in nature
4- If we assume that binding energy per nucleon for the nucleus of Neon ( 𝟐𝟎
𝟏𝟎𝑵𝒆) equals to
(161 MeV) then the average binding energy per nucleon for the nucleus of Neon with
units (MeV) equals:
a) 8.05
b) 16.1
c) 3220
d)1610
Q.2) What is the meaning of (nuclear binding energy)?
Nuclear binding energy: It is the energy required to disassemble the nucleus into protons
and neutrons.
Q.3) What is the particle which:
1) Has mass number equal one and an atomic number equals zero.
1) Neutron.
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