Please help me, what are micro and macrostates, what are accessible states?
I'd suggest you could start by having a look at:
Microstate (statistical mechanics) (Wikipedia)
The distribution of 9 units of energy among 6 identical particles (Hyperphysics)
Entropy (statistical thermodynamics) (Wikipedia)
Consider five coin tosses. I would call each of the possible outcomes a microstate (for example, HTTHT, THHHT, HHHTH, TTTTT and so on. H stands for heads and T for tails).
Now suppose I define a variable such as X=Total number of heads. For the microstates I have mentioned above, X will take values 2, 3, 4, 0 and so on. X is a macrostate. It tells you nothing about the specific configuration of the system. For example, X=4 will correspond to five microstates (HHHHT, HHHTH, HHTHH, HTHHH, THHHH), but you have no way of knowing which one.
An accessible state is a microstate the system can take without violating any laws governing the system.
I hope it is clear now.
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