## Pages

### What is entropy?

Entropy is a state function of a system, it depends only on the equilibrium state of the system. The chenge in entropy between initial and final equilibrium states is
$\Delta S=\int_{i}^{f}\frac{dQ}{T}$
where dQ is the infinitesimal heat transfer that takes place reversibly. The change in entropy for process, including irreversible one between given initial and final equilibrium state, is the same.The second law of thermodynamics may be expressed in terms of entropy, $\Delta S \geqslant 0$.
For reversible process  $\Delta S = 0$.
For irreversible process  $\Delta S > 0$.
Entropy is a measure of the disorder in a system. The second law states that the natural (irreversible) process tend to evolve to state of greater disorder, or from states of low probability to states of high probability.

### CBSE Class 9 physics notes on Newton's Laws of motion

Full length CBSE Class 9 physics notes on Newton's Laws of motion for study is now available.
To study the chapter visit the link given below
Newton's Laws of motion

### Force : Class 9 physics notes for CBSE and other boards

Class 9 physics notes on Force for CBSE and other board is now available. To read the notes visit the link

### Vector Differentiation full length notes for CSIR-NET/GATE/JAM

Full notes on vector Differentiation is now available at the website physicscatalyst.com covering following topics
1. Differentiation of vectors
2. Scalar and vector fields
3. Gradient of a scalar field
4. The operator delta
5. Divergence and curl of a vector
6. Product Rules
7. Second Derivative
For complete notes visit this link

### free physics questions with solutions for competitive exams : class 11 and class 12

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### CBSE class 10 Reflection of light full length notes

Class 9 physics notes on chapter Reflection of light is now available at the following link
CLASS 10 REFLECTION OF LIGHT NOTES (FULL LENGTH)

### CBSE class 9 motion full length notes

Class 9 physics notes on chapter motion is now available at the following link
CLASS 9 MOTION NOTES (FULL LENGTH)