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Answered on 19 Sep Exam Coaching/Engineering Entrance Coaching/GATE Coaching

Where are GATE oaching centres in Nellore?

 

Sachin Bonde

Tutor

Not sure but you can either approach in hyderabad for ACE engineering academy for good casses. If you are electronics/Electrical i provide online coaching and guidance with nice notes. thanks
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Lesson Posted on 15 Sep Exam Coaching/Engineering Entrance Coaching/GATE Coaching/Electrical Tuition/BTech Tuition/BTech Electrical & Electronics

lesson on Reactive power for Gate students

Surendar Reddy

I GOT gate AIR 179 rank in Electrical and electronics engineering. I have complete Knowledge of all...

1. What is reactive power? a) Reactive power is useful for machines to establish their working flux example: induction motors require reactive power to establish a rotating magnetic field(working flux). 2) What are sources of reactive power? a) 1. Synchronous alternator working with Lagging power... read more

1. What is reactive power?

a) Reactive power is useful for machines to establish their working flux

example: induction motors require reactive power to establish a rotating magnetic field(working flux).

2) What are sources of reactive power?

a) 1. Synchronous alternator working with Lagging power factor or overexcited synchronous alternator

2. Synchronous motor working with leading power factor or overexcited synchronous motor

3. Capacitor banks

4. Underground cables

3) What are sinks of reactive power?

1.Induction motors/generators

2. Inductors

3. overhead lines

4. Synchronous alternator working with Leading power or underexcited synchronous alternator

5. Synchronous motor working with lagging power factor or under excited synchronous motor

 

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Lesson Posted on 06 Sep CBSE/Class 11/Science/Chemistry CBSE/Class 11/Science/Physics Exam Coaching/Engineering Entrance Coaching/IIT JEE Coaching +1 Exam Coaching/Engineering Entrance Coaching/GATE Coaching less

All about entropy

Subrat Majhi

Fine at science 10th - 10cgpa 12th 90.60% Will make u aware of how science in linked with your life at every moment

Entropy, the measure of a system s thermal energy per unit temperaturethat is unavailable for doing useful work. Because work is obtained from ordered molecular motion, the amount of entropy is also a measure of the molecular disorder, or randomness, of a system. The concept of entropy provides deep... read more

Entropy, the measure of a system?s thermal energy per unit temperaturethat is unavailable for doing useful work. Because work is obtained from ordered molecular motion, the amount of entropy is also a measure of the molecular disorder, or randomness, of a system. The concept of entropy provides deep insight into the direction of spontaneous change for many everyday phenomena. Its introduction by the German physicist Rudolf Clausius in 1850 is a highlight of 19th-century physics.

The idea of entropy provides a mathematical way to encode the intuitive notion of which processes are impossible, even though they would not violate the fundamental law of conservation of energy. For example, a block of ice placed on a hot stove surely melts, while the stove grows cooler. Such a process is called irreversible because no slight change will cause the melted water to turn back into ice while the stove grows hotter. In contrast, a block of ice placed in an ice-water bath will either thaw a little more or freeze a little more, depending on whether a small amount of heat is added to or subtracted from the system. Such a process is reversible because only an infinitesimal amount of heat is needed to change its direction from progressive freezing to progressive thawing. Similarly, compressed gasconfined in a cylinder could either expand freely into the atmosphere if a valve were opened (an irreversible process), or it could do useful work by pushing a moveable piston against the force needed to confine the gas. The latter process is reversible because only a slight increase in the restraining force could reverse the direction of the process from expansion to compression. For reversible processes the system is in equilibrium with its environment, while for irreversible processes it is not.

To provide a quantitative measure for the direction of spontaneous change, Clausius introduced the concept of entropy as a precise way of expressing the second law of thermodynamics. The Clausius form of the second law states that spontaneous change for an irreversible process in an isolated system (that is, one that does not exchange heat or work with its surroundings) always proceeds in the direction of increasing entropy. For example, the block of ice and the stove constitute two parts of an isolated system for which total entropy increases as the ice melts.

By the Clausius definition, if an amount of heat Q flows into a large heat reservoir at temperature Tabove absolute zero, then the entropy increase is ?S = Q/T. This equation effectively gives an alternate definition of temperature that agrees with the usual definition. Assume that there are two heat reservoirs R1 and R2 at temperatures T1 and T2 (such as the stove and the block of ice). If an amount of heat Qflows from R1 to R2, then the net entropy change for the two reservoirs isentropy equationwhich is positive provided that T1 > T2. Thus, the observation that heat never flows spontaneously from cold to hot is equivalent to requiring the net entropy change to be positive for a spontaneous flow of heat. If T1 = T2, then the reservoirs are in equilibrium, no heat flows, and ?S = 0.

 

The condition ?S ? 0 determines the maximum possible efficiency of heat engines?that is, systems such as gasoline or steam engines that can do work in a cyclic fashion. Suppose a heat engine absorbs heat Q1 from R1and exhausts heat Q2 to R2 for each complete cycle. By conservation of energy, the work done per cycle is W= Q1 ? Q2, and the net entropy change isentropy equationTo make W as large as possible, Q2should be as small as possible relative to Q1. However, Q2 cannot be zero, because this would make ?Snegative and so violate the second law. The smallest possible value of Q2corresponds to the condition ?S = 0, yieldingentropy equationas the fundamental equation limiting the efficiency of all heat engines. A process for which ?S = 0 is reversible because an infinitesimal change would be sufficient to make the heat engine run backward as a refrigerator.

 

The same reasoning can also determine the entropy change for the working substance in the heat engine, such as a gas in a cylinder with a movable piston. If the gas absorbs an incremental amount of heat dQ from a heat reservoir at temperature T and expands reversibly against the maximum possible restraining pressure P, then it does the maximum work dW = PdV, where dV is the change in volume. The internal energy of the gas might also change by an amount dU as it expands. Then by conservation of energy, dQ = dU + PdV. Because the net entropy change for the system plus reservoir is zero when maximum work is done and the entropy of the reservoir decreases by an amount dSreservoir = ?dQ/T, this must be counterbalanced by an entropy increase ofentropy equationfor the working gas so that dSsystem + dSreservoir = 0. For any real process, less than the maximum work would be done (because of friction, for example), and so the actual amount of heat dQ? absorbed from the heat reservoir would be less than the maximum amount dQ. For example, the gas could be allowed to expand freely into a vacuum and do no work at all. Therefore, it can be stated thatentropy equationwith dQ? = dQ in the case of maximum work corresponding to a reversible process.

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Answered on 21 Sep Exam Coaching/Engineering Entrance Coaching/GATE Coaching

Shruti Kumari

Mathematics Teacher

Not, Commonly IIT Syllabus is Complex and Depth
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