Is changed or Has changed?

[Dolbo]

I got stumped by a student this morning Is it correct to say:

"The situation has changed" or
"The situation is changed"?

Another example: I redecorated my room. It was yellow but is now green.

Do I say "the room has changed" or the "the room is changed"?

And why

Thanks in advance

[bhaisahab]

I got stumped by a student this morning Is it correct to say:

"The situation has changed" or
"The situation is changed"?

Another example: I redecorated my room. It was yellow but is now green.

Do I say "the room has changed" or the "the room is changed"?

And why

Thanks in advance

The situation has changed, it is now a changed situation.
The room has changed, it is now a changed room.
Does that help?