Active to Passive

[girija]

The sentence 'Do not disturb the teacher.', when changed into the passive voice becomes, 'Let the teacher not be disturbed'. ( This is according to old grammar books. )

Is it correct if we say 'The teacher must not be disturbed' or 'The teacher should not be disturbed' ??

Or do we have to always start the command with the word 'let' if we want to change it to the passive form?

[Raymott]

The sentence 'Do not disturb the teacher.', when changed into the passive voice becomes, 'Let the teacher not be disturbed'. ( This is according to old grammar books. )

Is it correct if we say 'The teacher must not be disturbed' or 'The teacher should not be disturbed' ?? Yes

Or do we have to always start the command with the word 'let' if we want to change it to the passive form?

The answer depends on why you're asking the question. If you just want to learn English, yes you can say:
'The teacher must not be disturbed' or 'The teacher should not be disturbed' as a passive form alternative.

If you want to know what the official passive form of 'Do not disturb the teacher' is, maybe someone else has a different opinion.

[girija]

Yes, I wanted the official passive form. Thanks anyway.

[Abstract Idea]

In my opinion both passive sentences
'The teacher must not be disturbed' or 'The teacher should not be disturbed' indeed do not correspond to the active form of 'Do not disturb the teacher'.
From the options mentioned, only 'Let the teacher not be disturbed' does the
job.

Since it is in the imperative, a command, a guess you should always use
'let'. See the following examples:

Do not feed the animals - Let the animals not be fed.
Do not show this picture to Alice - Let Alice not be shown this picture.

You see "You must do something" is different from "Do something"

If we convert you other 'must' and 'should' suggestions to active, they would
look like:

The teacher must not be disturbed -> The students must not disturb the teacher
The teacher should not be disturbed -> The students should not disturb the teacher

[Irshad Alam]

Very smart answer. I do agree with you, ymnisky. Cheers!