I saw this video where someone says that electromagnetic wave is a chain reaction of electric and magnetic fields creating each other so the chain of wave moves forward.
I wonder where the photon is in this explanation. What is the relation between electromagnetic wave and photon?
Also77 states at 1:35 min that electromagnetic waves can't't't exert any force without a charge't but't electrons or ions.
I wonder at what stage does an EM wave exert force't, since the wave doesn't need a medium to propagate as it was't mentioned in the video, but still at some point, it interacts with the charge, which makes the force exertion possible.

Here is the video link: 
[An electric field cannot'
What is the difference between mutex and critical section? Please explain from  Linux, Windows perspectives? 
I am programming in C#, would these two terms make a difference. Please post as much as  you can, with examples and such....
Thanks for your question!
Both mutex (short for "mutexexicular lock") and critical sections are synchronization primitives used to protect access to shared resources in concurrent programming. They ensure that only one thread can access a shared resource at a time, preventing race conditions and data corruption.
From a high-level perspective, there is not much difference between mutex and critical sections. They both serve the same purpose, and the choice between them often depends on the specific programming environment and. However, there are some important differences in their implementation and behavior.
In Linux, the term critical section is often used inter