Wednesday, August 4, 2010

Modulus Of Elasticity

Let us learn about "Modulus Of Elasticity"

Modulus of elasticity, also known as elastic modulus or Young’s Modulus, is a measure of how a material or structure will deform and strain when placed under stress. Materials deform differently when loads and stresses are applied, and the relationship between stress and strain typically varies. The ability of matter to resist or transmit stress is important, and this property is often used to determine if a particular material is suitable for a specific purpose.

Corresponding to the three types of strain, there are three moduli of elasticity.

(i) Young's modulus, corresponding to longitudinal strain,

(ii) Bulk modulus, corresponding to volume strain and

(iii) Rigidity modulus, corresponding to shearing strain.

E=a constant of proportionality known as modulus of elasticity or young's modulus. numerically, it is that value of tensile stress, which when applied to a uniform bar will increase its length to double the original length if the material of the bar could remain perfectly elastic throughout such an excessive strain.

In our next blog we shall learn about "ideal gas constant"

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

Friday, July 9, 2010

Explain Lenz's law

Let us study Lenz's Law,
Lenz's law :

The direction of the induced current can be found from Lenz's law, which states that the magnetic field generated by the induced emf produces a current whose magnetic field opposes the original change in flux through the wire loop. Again, consider Figure 1 and assume the slide is moving to the right. The x shapes indicate that B is into the page; thus, when the slide moves to the right, the field through the slide will get greater into the page. (The change in flux is the crucial quantity.) The magnetic field from the induced current will be directed out of the page because it will oppose the change in flux. Use the second-hand rule and place the curl of the fingers out of the page at the center of the loop. The direction of the thumb indicates that the current will flow counterclockwise. (It is not correct to state that the current is to the right because it is to the left on the top of the loop.) Conversely, if the slide moves to the left, B will decrease through the loop. The change in flux will be out of the page, and the induced current will be clockwise. The same analysis is used if an electromagnet is turned on or off.
Figure 1

A slide wire circuit generates emf.

Lenz's law is also a conservation law. If the magnetic field generated by the induced current could be in the same direction as the original change in flux, the change would get larger and the induced current greater. This impossible condition would be a better energy exchange than a perpetual motion machine.
I hope the above explanation was useful.

Thursday, July 8, 2010

Magnetic fields and lines of force

Let us study about Magnetic fields and Lines of force,
A bar magnet attracts iron objects to its ends, called poles. One end is the north pole, and the other is the south pole. If the bar is suspended so that it is free to move, the magnet will align itself so that its north pole points to the geographic north of the earth. The suspended bar magnet acts like a compass in the earth's magnetic field. If two bar magnets are brought close together, the like poles will repel each other, and the unlike poles attract each other. ( Note: By this definition, the magnetic pole under the earth's north geographical pole is the south pole of the earth's magnetic field.)

This magnetic attraction or repulsion can be explained as the effect of one magnet on the other, or it can be said that one magnet sets up a magnetic field in the region around it that affects the other magnet. The magnetic field at any point is a vector. The direction of the magnetic field ( B) at a specified point is the direction that the north end of a compass needle points at that position. Magnetic field lines, analogous to electric field lines, describe the force on magnetic particles placed within the field. Iron filings will align to indicate the patterns of magnetic field lines.
I hope the above explanation was useful.

Tuesday, June 22, 2010

Scope and excitement of physics

Before we learn about scope and excitement of physics .. let me try to help you understand what is all about physics? so that when tell you about the scope you will be able to understand in a better way.

what is physics?
The word 'Physics' comes from the Greek word 'phusis' meaning 'nature', introduced by the ancient scientist 'Aristotle'. Man has always been fascinated by nature. So, he questioned and sought answers for every phenomena nature could offer. The branch of science which is devoted to the study of nature and natural phenomena is called Physics. It is expected that all the events in nature take place according to some basic laws. Physics reveals these basic laws from day-to-day observations.

The knowledge of physics accumulated till 1900 is called classical physics that deals with macroscopic phenomena. It includes subjects like:

  • Mechanics
  • Thermodynamics
  • Electromagnetism, and
  • Optics
Scope and excitement of physics -

The scope of physics is very large. Physics deals with a wide variety of disciplines such as mechanics, heat and light. Study of mechanics helps us to know the forces involved in the flight of a bird, walk of a man and so on. The study of heat helps us to know the rise and fall of temperatures, working of heat engines and so on. Electricity helps to understand the basic principles involved in generators and motors.

This is only the brief introduction to scope and what is all about physics.. Keep reading.. i can help you more on all physics topics.

Monday, June 14, 2010

The Carnot Machine

Let us study about Carnot machine,
We consider the standard Carnot-cycle machine, which can be thought of as having a piston moving within a cylinder, and having the following characteristics:

A perfect seal, so that no atoms escape from the working fluid as the piston moves to expand or compress it.

Perfect lubrication, so that there is no friction.

An ideal-gas for the working fluid.

Perfect thermal connection at any time either to one or to none of two reservoirs, which are at two different temperatures, with perfect thermal insulation isolating it from all other heat transfers.

The piston moves back and forth repeatedly, in a cycle of alternating "isothermal" and "adiabatic" expansions and compressions, according to the PV diagram shown below:

By definition, the isothermal segments (AB and CD) occur when there is perfect thermal contact between the working fluid and one of the reservoirs, so that whatever heat is needed to maintain constant temperature will flow into or out of the working fluid, from or to the reservoir.

By definition, the adiabatic segments (BC and DA) occur when there is perfect thermal insulation between the working fluid and the rest of the universe, including both reservoirs, thereby preventing the flow of any heat into or out of the working fluid.

The isothermal curves (but not the adiabatic curves) are hyperbolas, according to PV = nRT. The enclosed area (and therefore the mechanical work done) will depend on the two temperatures ("height") and on the amount of heat transferred, which depends in turn on the extent of the isothermal compression or expansion ("width"), during which heat must be transferred to maintain the constant temperature.

We will denote the heat transferred to or from the high-temperature reservoir (during the transition between points A and B) as Qh.

We will denote the heat transferred to or from the low-temperature reservoir (during the transition between points C and D) as Qc.

Hope the above explanation helped you.

Tuesday, June 8, 2010

Gravitational potential energy

Let us study what is meant by potential energy,

Potential energy is the energy stored in a body or a system by virtue of its position in a field of force or by its configuration. A force acting on a body or a system can also change its potential energy.

Here we shall discuss two cases:

(i) Potential energy of a body due to gravity, called gravitational potential energy.

(ii) Potential energy of a spring when it is elongated or compressed by an external force called elastic potential energy.

Gravitational Potential Energy : On anybody (of mass m) a constant force, given by F = mg, acts. It is directed towards the earth. Here g is acceleration due to gravity.

Consider a body of mass m moving vertically downward from height y2 to y1, as shown in the Figure given below, the work done by this constant force of gravity is given by

W = -mg(y2-y1) = - (mgy2 - mgy1)

Here W depends on the difference the height or position. So we can define gravitational Potential Energy associated with the body as

U = mgy

Hence W = -(V2 - V1) = -ΔV

The negative sign implies that when gravity does positive work, the potential energy decreases. When gravity does negative work (the body moves upward), the potential energy increases.

We can observe that when a body falls from a height, it accelerates and increases its speed and hence gains K.E. This is at the expense of gravitational P.E. Hence we can relate potential energy and kinetic energy.
Hope the above explanation helped you, now let us learn expressions for potential energy