Different types of spring

Engineering Students!!

Advantage and disadvantage of Capital budgeting.

Advantages of Capital Budgeting:
1.Capital budgeting helps a company to understand various risks involved in an investment opportunity and how these risks affect the returns of company.
2.It helps the company to estimate which investment option would yield the best possible return.
3.A company can choose a technique/method from various techniques of capital budgeting to estimate whether it is financially beneficial to take on a project or not.
4.It helps the company to make long term strategic investments.
5.It helps to make an informed decision about an investment taking into consideration all possible options.
6.It helps a company in a competitive market to choose its investments wisely.
7.All the techniques/methods of capital budgeting try to increase shareholders wealth and give the company an edge in the market.
8.Capital budgeting presents whether an investment would increase the company’s value or not.
It offers adequate control on expenditure for projects.
9.Also, it allows management to abstain from over investing and under investing.

Disadvantages of Capital Budgeting:
1.Capital budgeting decisions are for long term and are majorly irreversible in nature.
2.Most of the times, these techniques are based upon the estimations and assumptions as the future would always remain uncertain.
3.Capital budgeting still remains introspective as the risk factor and the discounting factor remains subjective to the manager’s perception.
4.A wrong capital budgeting decision taken can affect the long term durability of the company and hence it needs to be done judiciously by professionals who understands the project well.

(Collected)

Next Examination of ME 30th batch is Humanity and Accounting

What is Heat?

Heat is energy transferred between a system and its surroundings as a result of
a temperature difference. Energy that passes from a warmer body (with a higher
temperature) to a colder body (with a lower temperature) is transferred as heat.
At the molecular level, molecules of the warmer body, through collisions, lose
kinetic energy to those of the colder body. Thermal energy is transferred—“heat
flows”—until the average molecular kinetic energies of the two bodies become
the same, until the temperatures become equal. Heat, like work, describes
energy in transit between a system and its surroundings.

Not only can heat transfer cause a change in temperature but, in some
instances, it can also change a state of matter. For example, when a solid is heated,
the molecules, atoms, or ions of the solid move with greater vigor and eventually
break free from their neighbors by overcoming the attractive forces between
them. Energy is required to overcome these attractive forces. During the process
of melting, the temperature remains constant as a thermal energy transfer (heat)
is used to overcome the forces holding the solid together. Aprocess occurring at a
constant temperature is said to be isothermal. Once a solid has melted completely,
any further heat flow will raise the temperature of the resulting liquid.
Although we commonly use expressions like “heat is lost,” “heat is gained,”
“heat flows,” and “the system loses heat to the surroundings,” you should not
take these statements to mean that a system contains heat. It does not. The
energy content of a system, as we shall see in Section 7-5, is a quantity called
the internal energy. Heat is simply a form in which a quantity of energy may be
transferred across a boundary between a system and its surroundings.
It is reasonable to expect that the quantity of heat, q, required to change the
temperature of a substance depends on
• how much the temperature is to be changed
• the quantity of substance
• the nature of the substance (type of atoms or molecules)

Collected by, The Mechanic

Different type of Magnetic materials and their character

Different Types:

Magnetic materials are mainly 3 kinds by thedirection of induced flux and the stability of these. 
That's are,

1. Diamagnetic materials
E.g: Cadmium, Copper, Silver,
Bismuth, Tin, zinc, Gold, Niobium and its
compounds.

2. Paramagnetic materials
E.g: Aluminum, Calcium, Oxygen,
Platinum, Titanium and Chromium.

3. Ferromagnetic materials
E.g:
a. Ferromagnetic materials
E.g: Iron, Cobalt, Nickel
b. Anti-ferro magnetic materials
E.g: Ferrous oxide,
Manganese oxide, Zinc ferrite
c. Ferrimagnetic materials
E.g: Nickel ferrite, Manganese
ferrite, Ferrous ferrite

Diamagnetic Materials:
Definition:
These materials when placed in a
magnetic field, becomes weakly
magnetized in the direction opposite to
that of the applied field. There is no
permanent dipole moment in each atom.
The induced magnetic moment produced
in these materials during the application
of the external magnetic field decreases
the magnetic induction present in the
specimen.

Origin
A material contains a large number
of electrons and the orbits of these
electrons are randomly oriented in space.
The current that is produced due to
movement of electron in an orbit
produces magnetic field in a direction at
right angles to the plane of the orbit. This
magnetic field induces a magnetic
moment in the atom in a direction
opposite to it. These magnetic moments
are randomly oriented. Hence the
magnetic moments of all such electron
gets cancelled resulting in the net
magnetism equal to zero in the material.
When an external magnetic field is
applied to the material, rotation of
dipoles take place producing an induced

dipole moment: This induced dipole
moment opposes the applied field. The
magnetism which is created in a
direction opposite to that of the external
field is called diamagnetism.

Characteristics of diamagnetic materials:
1. Susceptibility ( m) of a diamagnetic
material is always negative. The relative
permeability μr < 1.
Example For Cadmium, ( m) = - 0.18 x10 -6
For Copper, ( m ) = - 0.086 x10 -6
For Silver, ( m ) = - 0.2 x10 -6
2. When magnetic field is applied, it
repels the magnetic lines of force. This
property is exhibited by
superconductors. Hence we call all
superconducting materials (at low
temperature) as perfect diamagnet. When
the temperature is increased beyond it
critical temperature, diamagnetism
suddenly disappears and it behaves like a
normal conducting material.
3. It does not depend on temperature and
the strength of applied magnetic field.
4. No magnetic moment is present in the
material.

Paramagnetic Materials

Definition:
Paramagnetic materials become
weakly ionized when placed in a
magnetic field in the same direction as
that of the applied field. It has
permanent dipole moment in each atom.
When external magnetic field is applied,
the induced magnetic moment is
produced which increase the magnetic
induction present in the specimen.
Origin
The orientation of the magnetic
moment along the direction of the
external field gives rise to
paramagnetism. The permanent magnetic
moment arises due to orbital motion of
electron around the nucleus and spin
motion of electron about its own axis.
The magnetic moment due to former
disappears due to the effect of electric
field of the neighbouring charges. But the
magnetic moment due to electron spin
are randomly oriented in the absence of
external field. When the external field is
applied, the magnetic moments tend to
align in the direction of the applied field
resulting in large magnetization. But due
to the thermal agitation of the atoms the
magnetic moments are partially aligned
in the direction of the external field
resulting in weak magnetization.

Characteristics
1. Susceptibility ( m) is positive and
small.
Example For aluminum, ( m ) =
0.065 x10 -6
For Calcium, ( m) = 1.10
x10 -6
The relative permeability μ r > 1.
2. When magnetic field is applied to
paramagnetic material, it is attracted
towards the centre of the material.
3. Susceptibility is inversely proportional
to absolute temperature of the material.
m α (1/T)
Curie’s law for high temperature m = (C/
T)
T = absolute temperature in Kelvin; C =
Curie constant
At low temperature m = C/(T-θ)
θ – paramagnetic curie temperature
θ is always very low. When the
temperature T < curie temperature, the
paramagnetics becomes diamagnetic.
4. Spin alignment: All spins are randomly
oriented.

Ferro Magnetic Materials

Definition:
Ferromagnetic materials are
strongly magnetized in the direction of
the applied magnetic field. It possesses
enormous permanent magnetic moment
in each atom. When external magnetic
field is applied, a large amount of
induced magnetic moment is produced
which increases the magnetic induction
present in the specimen.
Origin
The presence of permanent
magnetic moments in the atoms or
molecules in the specimen gives rise to
ferromagnetism as this magnetic moment
align themselves in the same direction as
that of the external field. The exchange
interaction between unpaired electrons
of adjacent atoms in the crystal lattice
gives rise to local molecular magnetic
field resulting in spontaneous
magnetization.

Characteristics
1. Magnetic susceptibility value is large
and positive. The temperature
dependence of susceptibility for
ferromagnetic materials is said to be
complex.
2. When magnetic field is applied to a
ferromagnetic material, the magnetic
lines of force are strongly attracted by
the specimen.
3. Ferromagnetic materials exhibit
hysteresis. Even if the magnetic field is
removed from the material, it retains the
magnetism due to spontaneous
magnetization. They have permanent
dipole moment.
4. The permeability of a ferromagnetic
material is not a constant, as magnetic
induction (B) does not vary linearly with
magnetic field strength (H).
5. When the temperature of the
ferromagnetic material is greater than its
Curie temperature, then ferromagnetic is
converted into a paramagnetic material.

Antiferromagnetism and Ferrimagnetism:
The only type of magnetic order
which has been considered thus far is
ferromagnetism, in which, in the fully
magnetized state, all the dipoles are
aligned in exactly the same direction.
There are, however, substances which
show different types of magnetic order.
In antiferromagnetic materials such as Cr
and MnO, the dipoles have equal
moments, but adjacent dipoles point in
opposite directions. Thus the moments
balance each other, resulting in a zero
net magnetization.
In ferromagnetic materials (also called
ferrites) such as MnFe 2 O4 , the
magnetic moments of adjacent ions are
antiparallel and of unequal strength. So
there is a finite net magnetization. By
suitable choice of rare-earth ions in the
ferrite lattices it is possible to design
ferromagnetic substances with specific
magnetizations for the use in electronic
components.

Posted by,
Shaiful islam majumder
ME 1/2,  Dhaka university of engineering and Technology

DUET Chapter 2

DUET Chapter 1

Physics

Chemistry

mathematics

Paul's exclusion principle

The Pauli Exclusion Principle states that, in an atom or molecule, no two electrons can have the same four electronic quantum numbers . As an orbital can contain a maximum of only two electrons, the two electrons must have opposing spins.
This means if one is assigned an up-spin ( +1/2), the other must be down-spin (-1/2).

Electrons in the same orbital have the same first three quantum numbers,
e.g.,
, , for the 1 s subshell. Only two electrons can have these numbers, so that their spin moments must be either
or . If the 1 s orbital contains only one electron, we have one
value and the electron configuration is written as 1 s (corresponding to hydrogen). If it is fully occupied, we have two values, and the electron configuration is 1 s (corresponding to helium). Visually these two cases can be represented as
As you can see, the 1 s subshell can hold only two electrons and when filled the electrons have opposite spins.

Contributors
Sarah Faizi (University of California Davis)
Dr. Craig Fisher (Japan Fine Ceramics Center)

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