valence shell

Let us learn about "valence shell"

The outermost shell of an atom is called its Valence shell. It is the decisive shell during a chemical reaction. The electrons of only this outermost shell are involved during chemical combinations; electrons are either given out from the outermost shell, or accepted into the outermost shell, or shared with the electrons in the outermost shell of another element.

Valance shell electronic configuration is the representation of the participation of electrons in orbits of atom.

The electrons in an atom are filled by the three basic principles:

AufBau Principle

Pauli Exclusion Principle

Hund’s Rule

As per AufBau’s principle, the electrons will be filled first in orbital’s with lower energy like 1s will be filled first before 2s and 2s will be filled before 2p.

As per Pauli’s exclusion principle, no two electrons within a particular atom can have identical can have identical quantum numbers. In similar meaning it says that two electrons occupy the same orbital must have opposite spins.

As per Hund’s rule, when an electron come to an atom, and has to choose between two or more orbital’s of same energy, then the preference will be given to empty orbital rather than the occupied one. As more electrons will be occupied, they tend to follow half-filled and fully filled rule.

In our next blog we shall learn about "balance chemical equations calculator"

I hope the above explanation was useful.Keep reading and leave your comments.

Explain Faraday's law

Let us study about Faraday's law,

Faraday's law :

Changing the magnetic flux through a loop of wire induces a current. Faraday's law states that the emf induced in a wire is proportional to the rate of the flux through the loop. Mathematically,
where N is the number of loops, ΔΦ is the change of flux in time, Δ t. The minus sign indicates the polarity of the induced emf.

The preceding equation is easy to use when the flux is set up by an electromagnet. If the electromagnet is turned on or off, the induced emf is equal to the number of turns in the loop times the rate of change of flux. The flux might also be changed through a loop altering the size of the loop. Imagine a slide wire, as shown in Figure 1 , where l is the length of the wire that moves in contact with the U-shaped wire. In this case, ε= Blv, where v is the velocity of the sliding length.Note that this induced emf is indistinguishable from that of a battery and that the current is still just the rate of the motion of charges; therefore, Ohm's law and other relationships for currents in wires are still valid.
Hope the above explanation was helpful.

Transverse and longitudinal waves

Transverse and longitudinal waves :

On the left side of Figure 1 , a pulse travels on a string. As the pulse passes point P on the string, the point moves up and then back to the equilibrium position. Each segment of the rope moves only perpendicular to the motion of the wave. This type of traveling wave is called a transverse wave.

Figure 1

Transverse (a) and longitudinal (b) waves.

The right side of Figure 1 shows the pulse propagated along a stretched spring. In this case, the individual points along the medium (the spring) travel back and forth parallel to the motion of the pulse. This type of traveling wave is called a longitudinal wave. Sound waves are longitudinal waves.
I hope the above explanation was helpful.

Summary to Reflection of Light

In this lesson .. let me try to help you on reflection of light.

Introduction -

It is a matter of common experience that the objects inside a dark room, which are invisible, become visible when the room is illuminated by a source of light. Thus light can be defined as the external cause responsible for the sensation of vision.

When a ray of light falls on any surface, a part of the light is sent back to the same medium. This phenomenon where the incident light falling on a surface is sent back to the same medium is known as reflection.

There are two types of reflection of light:

• Regular reflection

• Irregular reflection

Regular reflection -

Regular Reflection on a Smooth Surface

Regular reflection takes place when a ray of light is incident on a polished smooth surface like a mirror. Here the reflected ray of light moves only in a fixed direction.

Irregular reflection-

Irregular reflection or diffused reflection takes place when a ray of light is incident on a wall or wood, which is not smooth or polished. In this case, the different portions of the surface reflect the incident light in different directions. In such cases no definite image is formed, but the surface becomes visible. It is commonly known as scattering of light. Thus diffused reflection makes non-luminous objects visible.

Not all light, which hits an object, is reflected. Some of the incident light is absorbed. The brightness of an object depends on the intensity of the incident light and also on the reflectivity of the object.

If a surface allows the entire incident light to undergo regular reflection then it will become invisible.

I hope my information on this topic is more helpful to you .. Keep reading and leave your comments..

Explain Centripetal acceleration

Let us study about centripetal acceleration,

Property of the motion of an object traveling in a circular path. Centripetal describes the force on the object, directed toward the centre of the circle, which causes a constant change in the object's direction and thus its acceleration. The magnitude of centripetal acceleration a is equal to the square of the object's velocity v along the curved path divided by the object's distance r from the centre of the circle, or a = v2/r.

The radial component of the acceleration of a particle or object moving around a circle, which can be shown to be directed toward the center of the circle. Also known as radial acceleration.

The gravitational acceleration at earth's surface is 9.8 m/s/s. The centripetal acceleration on earth's surface at
the equator is 0.006 m/s/s. At earth's equator the gravitational force and the centripetal force are both in the same vertical direction. However, at other places on earth's surface the centripetal force is at an angle equal to a place's latitude, and the centripetal force is reduced due to reduced distance to the axis of earth's rotation. One would deduce that at these places there's a horizontal component of centripetal force, that would cause a person to lean slightly toward earth's pole to maintain his or her balance.
Hope the above explanation was helpful.

Elasticity of solids

Let us study about elasticity of solids,
Elasticity is the ability of a solid to return to its initial shape after having an outside force applied to it and then removed. An object with a high level of elasticity is able to have its shape changed a great deal, while still being able to return to its original form. Solids with little or no elasticity either become permanently deformed or break when a force is applied to them. The term elasticity can also be used to describe the ability of processes or systems to stretch or be flexible.

Due to the molecular make up of solids, liquids, and gases, they all react differently to outside stresses. The molecules that make up a solid are very close together and are found in a precise arrangement. This means that there is little room for give when a force is applied to a solid. The molecules of liquids and gases are spread further apart, and move more freely than those of solids. When a force is applied to liquids and gases, they can either flow away from or around the force, or be compressed a great deal, unlike most solids.

There are three different classes of force, or stresses, that can affect solid objects. The first is tension, also called stretching, which occurs when equal but opposite forces are applied to either end of the object. Compression is the second type of stress, which occurs when an object is put under pressure, or the force pushing on the solid is at 90 degrees to its surface. Imagine crushing an empty paper towel roll between your hands with your hands at either end. The final type of stress is shear, which happens when the force is parallel to the surface of the object.
Hope the above explanation helped you, now let us study about states of matter.

Center of Mass

Let us learn about center of mass,

Every object has a center of mass, which can be thought of as the point that is as close as possible to every piece of an object. Usually the center of mass is found within the object. For example, the center of mass of a ball is the very middle of the ball, and the center of mass of a book is the middle of the book. Where do you think the center of mass of your pencil is? How about the center of mass of your body? Talk about this with you mentor.

The center of mass determines whether or not something will fall over. Imagine pushing over a refrigerator. At the beginning, the center of mass is directly over where the fridge touches the ground.

If you push the refrigerator a little, it will fall back into place. If, however, you push it enough so that the center of mass is past the piece of the fridge that is touching the ground, it will fall.
Hope the above explanation helped you, now let us study about Force.

Hydraulic Machines

Let us learn about Hydraulic Machines,
Let us now consider what happens when we change the pressure on a fluid contained in a
vessel. Consider a horizontal cylinder with a piston and three vertical tubes at different
points. The pressure in the horizontal cylinder is indicated by the height of liquid column in
the vertical tubes.It is necessarily the same in all. If we push the piston, the fluid level rises in
all the tubes, again reaching the same level in each one of them.
This indicates that when the pressure on the cylinder was increased, it was distributed
uniformly throughout. We can say whenever external pressure is applied on any part of a
fluid contained in a vessel, it is transmitted undiminished and equally in all directions.
This is the Pascal’s law for transmission of fluid pressure and has many applications in
daily life.

A number of devices such as hydraulic lift and hydraulic brakes are based on the Pascal’s
law. In these devices fluids are used for transmitting pressure. In a hydraulic lift as
shown in Fig. two pistons are separated by the space filled with a liquid.
Schematic diagram illustrating the principle behind the hydraulic lift, a device used to lift heavy loads.

A piston of smallcross section A1 is used to exert a force F1 directly on the liquid. The pressure P = F1/A1 is
transmitted throughout the liquid to the larger cylinder attached with a larger piston of area A2,
which results in an upward force of P × A2. Therefore, the piston is capable of supporting a
large force (large weight of, say a car, or a truck, placed on the platform) F2 = PA2 = F1A2 / A1 . By changing the force at A1, the platform can be moved up or down. Thus, the applied force has
been increased by a factor of A2/A1 and this factor is the mechanical advantage of the device.
Hope the explanation helped you, now let us learn about Transmission of Pressure in Liquids.

Atmospheric Pressure and Gauge Pressure

Let us learn about Atmospheric pressure,
The pressure of the atmosphere at any point is
equal to the weight of a column of air of unit
cross sectional area extending from that point
to the top of the atmosphere. At sea level it is
1.013 × 105 Pa (1 atm). Italian scientist
Evangelista Torricelli (1608-1647) devised for
the first time, a method for measuring
atmospheric pressure. A long glass tube closed
at one end and filled with mercury is inverted
into a trough of mercury as shown in Fig.
This device is known as mercury barometer. The
space above the mercury column in the tube
contains only mercury vapour whose pressure
P is so small that it may be neglected. The
pressure inside the column at point A must
equal the pressure at point B, which is at the
same level. Pressure at B = atmospheric
pressure = Pa
Pa = ρgh
where ρ is the density of mercury and h is the height of the mercury column in the tube.
In the experiment it is found that the mercury column in the barometer has a height of about
76 cm at sea level equivalent to one atmosphere (1 atm). This can also be obtained using the
value of ρ in Eq. A common way of stating pressure is in terms of cm or mm of mercury
(Hg). A pressure equivalent of 1 mm is called a torr (after Torricelli).
1 torr = 133 Pa.
The mm of Hg and torr are used in medicine and physiology. In meteorology, a common unit
is the bar and millibar.
1 bar = 105 Pa
Now, let us learn Measurement of Atmospheric Pressure.

Variation of Pressure with Depth

Let us learn about Variation of Pressure with Depth.
Consider a fluid at rest in a container. In Fig. point 1 is at height h above a point 2.
The pressures at points 1 and 2 are P1 and P2 respectively. Consider a cylindrical element of
fluid having area of base A and height h. As the fluid is at rest the resultant horizontal forces
should be zero and the resultant vertical forces should balance the weight of the element. The
forces acting in the vertical direction are due to the fluid pressure at the top (P1A) acting
downward, at the bottom (P2A) acting upward. If mg is weight of the fluid in the cylinder we
have (P2 − P1) A = mg
Now, if ρ is the mass density of the fluid, we have the mass of fluid to be m = ρV= ρhA so
that
P2 − P1= ρgh
Fluid under gravity. The effect of gravity is illustrated through pressure on a vertical
cylindrical column.

Pressure difference depends on the vertical distance h between the points (1 and 2), mass
density of the fluid ρ and acceleration due to gravity g. If the point 1 under discussion is
shifted to the top of the fluid (say water), which is open to the atmosphere, P1 may be replaced
by atmospheric pressure (Pa) and we replace P2 by P. Then Eq. gives
P = Pa + ρgh
Thus, the pressure P, at depth below the surface of a liquid open to the atmosphere is
greater than atmospheric pressure by an amount ρgh. The excess of pressure, P − Pa, at
depth h is called a gauge pressure at that point.
Hope the above explains about Variation of Pressure with Depth, now let me explain about Vapour pressure.

Pascal’s Law

Let me give you some introduction on pascal's law

The French scientist Blaise Pascal observed that the pressure in a fluid at rest is the same at all points if they are at the same height. This fact may be demonstrated in a simple way.
Fig : Proof of Pascal’s law. ABC-DEF is an element of the interior of a fluid at rest. This element is in the form of a right angled prism. The element is small so that the effect of gravity can be ignored, but it has been enlarged for the sake of clarity.

Figure shows an element in the interior of a fluid at rest. This element ABC-DEF is in the
form of a right-angled prism. In principle, this prismatic element is very small so that every
part of it can be considered at the same depth from the liquid surface and therefore, the effect
of the gravity is the same at all these points. But for clarity we have enlarged this element.
The forces on this element are those exerted by the rest of the fluid and they must be normal to
the surfaces of the element as discussed above. Thus, the fluid exerts pressures Pa, Pb and Pc on
this element of area corresponding to the normal forces Fa, Fb and Fc as shown in Fig. 10.2 on the faces BEFC, ADFC and ADEB denoted by Aa, Ab and Ac respectively. Then Fb sinθ = Fc, Fb cosθ = Fa (by equilibrium)Ab sinθ = Ac, Ab cosθ = Aa (by geometry)
Thus,Hence, pressure exerted is same in all directions in a fluid at rest. It again reminds us that like other types of stress, pressure is not a vector quantity. No direction can be assigned
to it. The force against any area within (or bounding) a fluid at rest and under pressure is
normal to the area, regardless of the orientation of the area.

Pressure

Let me explain what is pressure,
Imagine when a sharp needle when pressed against our skin pierces it. Our skin, however, remains intact when a blunt object with a wider contact area (say the back of a spoon) is pressed against it with the same force. If an elephant were to step on a man’s chest, his ribs would crack. A circus performer across chest chest a large, light but strong wooden plank is placed first, is saved from this accident. Such everyday experiences convince us that both the force and its coverage area are important. Smaller the area on which the force acts, greater is the impact. This concept is known as pressure.

When an object is submerged in a fluid at rest, the fluid exerts a force on its surface. This force is always normal to the object’s surface. This is so because if there were a component of force parallel to the surface, the object will also exert a force on the fluid parallel to it; as a consequence of Newton’s third law. This force will cause the fluid to flow parallel to the surface.

Since the fluid is at rest, this cannot happen. Hence, the force exerted by the fluid at rest has
to be perpendicular to the surface in contact with it. This is shown in Figure.
Hope the above example explains you about pressure, now let me give you more examples.

Uniform Motion and Non-uniform Motion

Uniform motion and non - uniform Motion are the important one in the newton's law of motion. This helps in understanding more on law of motions and its importance in our day today life.

The distances covered by car A and car B with respect to time is given below.

Car A

Time in Seconds	0	5	10	15	20	25	30	35
Distance covered in meters	0	10	20	30	40	50	60	70

Car B

Time in Seconds	0	5	10	15	20	25	30	35
Distance covered in meters	0	5	15	20	30	60	65	75

The car A travels equal distances in equal intervals of time whereas the car B does not cover equal distances in equal intervals of time. That is, motion of car A is an example of uniform motion whereas that of car B is that of non-uniform motion.

When a body covers equal distances in equal intervals of time then the body is said to describe uniform motion. When a body moves unequal distances in equal intervals of time or vice-versa, then the body is said to describe non-uniform motion.

This was the sample help to understand on Uniform Motion and Non - Uniform Motion. Hope you enjoyed reading this. I can still help you understand better on all topics on math help.

Three laws of Gravity

As we have discussed enough on newton's law of gravity.. let me also help you go through on the major three law of gravity.
what is the meaning of gravity?
When you throw a ball, book or a stone they will be pulled back to the ground. They experience a force to reach the ground. That force is called as "Gravity" or "Gravitation"
Three law of gravity -
As we already discussed that Newton stated three laws of gravity. These are also called as "Laws of Motion". The main concepts in the three laws of gravity are Velocity, Force, Mass and Acceleration.

1. First Law: The First law of gravity is also know as 'Law of Inertia'.It states that there is no change in a object unless and until some external force acting up on it. It also states that an object moves in a straight line until an additional force acts upon it.
2. Second Law: The acceleration of the object will be directly proportional to the net force applied on it and at the same time the acceleration of the object is inversely proportional to the mass of the object. Clearly, if we increase the force on an object the acceleration of that object also increases. At the same time if we increase the mass of the object the acceleration will decrease.
3. Third Law: This is also called as 'Law of Action-Reaction'. It states that there is always equal and opposite reaction for any actions

I hope my information would have helped you to understand on the law of gravity. I would also like to pass on one important message to you all. I had been go through TutorVista online eduction website .. they have the more specified and relevant content on all the subjects. If you need more help on any subject go on to the web site - www.tutorvista.com. This is one of the coolest web site which i have ever found and they do all wonders to help us in all subjects. If this is more interesting to you then share this information to others as well . keep reading .. if i make sense leave your comments.....

Effect of Gravity on Falling Objects

I have and important lesson to share with you all that is all about effects of gravity on falling objects.
Acceleration Due to Gravity of the Earth -
Gravity of the earth can be imagined to be a sphere made of a large number of concentric spherical shells with the smallest one at the center and the largest one at its surface. A point outside the earth is obviously outside all the shells. Thus, all the shells exert a gravitational force at the point outside just as if their masses are concentrated at their common center according to the result stated in the last section. The total mass of all the shells combined is just the mass of the earth. Hence, at a point outside the earth, the gravitational force is just as if its entire mass of the earth is concentrated at its center.
Gravitational Potential Energy -
The force of gravity is a conservative force and we can calculate the potential energy of a body arising out of this force, called the gravitational potential energy.
Weightlessness -
Weight of an object is the force with which the earth attracts it. We are conscious of our own weight when we stand on a surface, since the surface exerts a force opposite to our weight to keep us at rest.
Newton’s law of universal gravitation states that the gravitational force of attraction
between any two particles of masses m1 and m2 separated by a distance r has the magnitude
where G is the universal gravitational constant, which has the value 6.672 ×10–11 N m2 kg–2.
This was just and introduction to Effects of Gravity. Keep reading ... will discuss more on physics help may be in next lesson

MOTION AND FORCES

let me help you all about motion and forces and its factors. we were been learning all about newton's law of motion. Now i will also help you go through Motion and Forces.

Motion and Forces -

• Problems involving constant speed and average speed
• Newton's First Law of Motion
• Newton's Second Law of Motion
• Newton's Third Law of Motion
• Universal Law of Gravitation
• Effect of gravity on an object at the surface of the Earth
• Applying a force to an object perpendicular to the direction of its motion
• Circular motion
• Two-dimensional trajectory problems
• Two-dimensional vectors into their components and calculate the magnitude and direction of a vector from its components
• Two-dimensional problems involving balanced forces
• Problems in circular motion, using the formula for centripetal acceleration in the following form: a=v²/r
• Problems involving the forces between two electric charges at a distance (Coulomb's Law) or the forces between two masses at a distance (Universal gravitation)

With these... you might have come to an conclusion all about motion and forces. may be on the next lesson i will help you go through on Motion for a Body Moving under Gravity

Nuclear Energy and Chemical Energy

Nuclear energy is released when very small particles of matter split or combine. After the split or combination, they result in small particles or heavy particle. The rest of the mass is changed into energy. This process of changing mass into energy produces the energy.

Examples on nuclear energy and chemical energy-

Following are you the Examples on nuclear energy and chemical energy

Example :-

What is the function of control rods in a nuclear reactor? Explain, what is the material used for these rods?

Suggested Answer:-

Control rods regulate the rate of fission by absorbing the excess neutrons and prevent the chain reaction. Deeper the rods are placed slower the process.

The material used is boron or cadmium alloyed with aluminium or steel.

Let me also help you more on energy levels like work, energy and power . In the following lesson let me help you go through Environmental Laws. Keep reading and give your valuable suggestion and comments.

THE LAW OF CONSERVATION OF ENERGY

THE LAW OF CONSERVATION OF ENERGY -
Energy is an important one for us to live with. It not only increases out productivity power but also conservation of energy as well.
In the previous lesson we have discussed mechanical energy. We have seen that it can be classified into two distinct categories : one based on motion, namely kinetic energy; the other on configuration (position), namely potential energy. Energy comes in many a forms which transform into one another in ways which may not often be clear to us.

Law of Conservation of Energy Statement

The Law of Conservation of Energy states that "the total energy of an isolated system is conserved or said to be constant over time". It can also be said that "energy cannot be created or destroyed , but it can be transformed from one form to another form".

Following the major factor for conservation of Energy

• Heat
• Chemical Energy
• Electrical Energy
• The Equivalence of Mass and Energy
• Nuclear Energy

I hope that i have helped you on understanding all about conservation of energy. let me also help you go through about The Principle of Conservation of Energy in the following lesson. keep reading and keep in touch with your valuable comments.

Examples of Kinetic Energy

As we understood what is all about kinetic Energy in the previous lesson, let me also go through on Examples of kinetic Energy. This will help you not only on examples but also kinetic energy and temperature.
Kinetic energy:
Kinetic energy produced by a body due to its motion is called kinetic energy. The kinetic energy is equal to one half the product of mass and square of velocity of the body
Temperature:
One of the thermodynamic energy is temperature. It is related to average energy of motion
Examples of Kinetic Energy:

I would like to list down all the examples of Kinetic Energy. All moving objects have kinetic energy. Keeping this point in mind we can illustrate some examples of kinetic energy

1. A moving car
2. Water falling from a height in waterfalls
3. Electrons revolving around the nucleus
4. Earth orbiting the sun
5. A swinging pendulum
6. Satellites revolving around the planets
7. A walking man
8. A moving rocket or spacecraft
9. A bullet fired from a gun
10. A child playing a computer game
11. A spinning top
12. Water stored in the dam has potential energy.When it flows down the Potential energy gets converted into Kinetic energy.
13. A rocket fired from the launch vehicle.
14. A person skipping
15. A police running behind a thief
16. Mangoes falling from a mango tree
17. A diver undergoing sky diving
18. A person swimming
19. A crawling baby
20. A bucket of water undergoing vertical or horizontal motion

In short any example of motion you consider, it has kinetic energy associated with it.

I hope i took your time in a productive way. keep reading .... May in the next lesson let me help you understand on Momentum and kinetic energy.

What is Kinetic Energy

Introduction of Kinetic Energy -
Kinetic energy is a form of energy which is related to the motion of the particle.If a body is at rest then its kinetic energy will be zeroinetic energy is a form of energy which is related to the motion of the particle.If a body is at rest then its kinetic energy will be zero.

What is Kinetic energy:
I would also like to post an example on what is Kinetic Energy. Consider a body of mass 'm' moving with a velocity 'v'. The kinetic energy associated with the particle is given by
KE = 1/2mv^{2
Types of Kinetic Energy-}
Following are the types of Kinetic energies
1. Translational kinetic energy - possessed by a body undergoing straight line motion
2. Rotational kinetic energy - possessed by rotating objects
Have you come to an conclusion on what is all about Kinetic Energy. I would also like to share my thoughts with you on Examples of Kinetic Energy. Keep reading and leave your comments to help me help you better.........

Physics in relation to Science, Society and Technology

Physics is always in relation to People, Society and technology. The relation between physics, technology and society can be seen in many examples. The discipline of thermodynamics arose from the need to understand and improve the working of heat engines. The steam engine, as we know, is inseparable from the Industrial Revolution in England in the eighteenth century, which had great impact on the course of human civilization. Sometimes technology gives rise to new physics; at other times physics generates new technology. An example of the latter is the wireless communication technology that followed the discovery of the basic laws of electricity and magnetism in the nineteenth century. The applications of physics are not always easy to foresee.

Below are the few examples of some physicists from different countries of the world and their major contribution
Physics is the study of nature and natural phenomena. Physicists try to discover the rules
that are operating in nature, on the basis of observations, experimentation and analysis.
Physics deals with certain basic rules/laws governing the natural world. What is the nature of physical laws? We shall now discuss the nature of fundamental forces and the laws that
govern the diverse phenomena of the physical world.

Scope and Excitement of Physics

In this lesson lets try to learn more on what is all about Physics and its scope and excitement of Physics.

What is Physics?
The word Physics comes from a Greek word meaning nature. Its Sanskrit equivalent is Bhautiki that is used to refer to the study of the physical world. A precise definition of this discipline is neither possible nor necessary. We can broadly describe physics as a study of the basic laws of nature and their manifestation in different natural phenomena.

The scope of physics is described briefly in the next section. Here we remark on two principal thrusts in physics : unification and reduction.

Scope and Excitement of Physics.
We can get some idea of the scope of physics by looking at its various sub-disciplines. Basically,
there are two domains of interest : macroscopic and microscopic. The macroscopic domain
includes phenomena at the laboratory, terrestrial and astronomical scales. The microscopic domain includes atomic, molecular and nuclear phenomena*.
Physics is exciting in many ways. To some people the excitement comes from the elegance and
universality of its basic theories, from the fact that a few basic concepts and laws can explain
phenomena covering a large range of magnitude of physical quantities.

In the following lessons lets try to learn Physics in relation to Science, Society and technology.

Huygens Principle

In this lesson lets try to examine on Huygens Principle. Before we start lets try to know
" What is Huygens Principle?"
Huygens’ Principle (HP) contains both the principle of action-at-proximity and the superposition principle of waves . Although the propagation of sharp, non-spreading wave fronts is included in Huygens’ original formulation, it can be left out without touching those principles

We would first define a wavefront along with the wave theory : when we drop a small stone on a calmpool of water, waves spread out from the point of impact. Every point on
the surface starts oscillating with time.

If we have a point source emitting waves uniformly in all directions,
then the locus of points which have the same amplitude and vibrate in
the same phase are spheres and we have what is known as a spherical
wave as shown in Fig. At a large distance from the source, a small portion of the sphere can be considered as a plane and we have
what is known as a plane wave

Now, if we know the shape of the wavefront at t = 0, then Huygens
principle allows us to determine the shape of the wavefront at a later
time τ. Thus, Huygens principle is essentially a geometrical construction, which given the shape of the wavefront at any time allows us to determine the shape of the wavefront at a later time. Let us consider a diverging wave and let F1F2 represent a portion of the spherical wavefront at t = 0