Learn Hardcore Russian: Проверь, включена ли камера, прежде чем начинать урок. - Check whether the camera is on before starting the lesson.

Use Проверь when speaking to:
- a friend
- a classmate
- a child
- anyone you ты-address
Проверьте is the formal / plural imperative:
- to one person you address as вы (teacher, stranger, client, etc.)
- to a group of people

So the sentence assumes you’re talking informally to one person. Formally, it would be:
Проверьте, включена ли камера, прежде чем начинать урок.

Why is the verb проверить (perfective: Проверь) used, and not проверять (imperfective: Проверяй)?

Russian often uses the perfective in imperatives when the action is:

single, complete, with a clear result
something you want done and finished (“check it once now”)

Проверь = “(go and) check (and be done with it).”

Проверяй (from imperfective проверять) sounds like:

“keep checking, keep on checking” (repeated / ongoing), or
can be more emotional / bossy in tone, depending on context

Here we want a one-time, result-oriented action (make sure the camera is on), so the perfective Проверь is natural.

What exactly does ли mean in включена ли камера?

Ли is a particle used to mark yes/no questions, similar to an embedded “whether / if” in English.

Камера включена? – “Is the camera on?” (direct question)
включена ли камера – “whether the camera is on” / “if the camera is on” (inside a bigger sentence)

So:

Проверь, включена ли камера…
≈ “Check whether the camera is on before starting the lesson.”

In embedded clauses like this, Russian prefers ли to turn the statement into a “whether/if” idea.

Why is the word order включена ли камера and not ли включена камера?

The particle ли normally comes right after the word being questioned / focused and typically in second position in its clause.

Here the clause is essentially:

Камера включена. – “The camera is on.”

To turn it into a “whether” clause, Russians usually place ли right after the predicate (here: включена):

включена ли камера – literally: “on ли the camera (is)”

Putting ли first (ли включена камера) is ungrammatical in standard Russian. The normal pattern is:

Он придёт. → Придёт ли он? (Will he come?)
Камера включена. → Включена ли камера? (Is the camera on?)

In our sentence we’re not asking directly; we’re embedding that question: Проверь, включена ли камера…

What form is включена? Why not something like включенная or включённая?

Включена here is a short-form passive participle (traditionally called a “short adjective”), from the verb включить (“to turn on”).

включить → включённый (full participle, adjective: “switched-on”)
short form: включён / включена / включено / включены

Short forms are used:

as predicative parts, like English “is on / is turned on”:
- Камера включена. – “The camera is on.”

Full forms (e.g. включённая) are more attributive (“the switched-on camera”) or descriptive in style:

включённая камера стоит на столе. – “The camera that is on is on the table.”

In our sentence, включена is a short predicative form agreeing with камера (feminine singular):

masculine: включён
feminine: включена
neuter: включено
plural: включены

Why is there no word for “is” (like есть) in включена ли камера?

In Russian, in the present tense, the verb “to be” (быть) is usually omitted:

Камера включена. literally: “Camera on.” → “The camera is on.”
Он врач. – “He (is a) doctor.”

You would only see есть in present tense in special emphatic or contrastive contexts, not in a normal sentence like this.

So включена ли камера already means “is the camera on?”
Adding есть (включена ли камера есть) would be wrong here.

Which case is камера in, and why?

Камера is in the nominative case, singular, because in the clause включена ли камера it is the subject:

камера (subject)
включена (predicative / short-form participle: “on”)

It’s the same structure as:

Камера включена. – “The camera is on.”

Subject → nominative is the default pattern.

What does прежде чем mean, and why is there a comma before it?

Прежде чем is a conjunction meaning “before (doing something).” It introduces a subordinate clause of time.

The structure here is:

Main clause: Проверь, включена ли камера,
Subordinate clause of time: прежде чем начинать урок. – “before starting the lesson.”

In Russian punctuation, subordinate clauses are normally separated from the main clause by a comma, so we write:

…, прежде чем …

Thus the comma is required by Russian punctuation rules, not optional.

Why is it прежде чем начинать урок (imperfective начинать) and not прежде чем начать урок (perfective начать)?

Both are possible in modern Russian, but they have slightly different nuances:

прежде чем начать урок (perfective):
- focuses on the single act of beginning the lesson
- very common and sounds completely neutral:
  - Проверь, включена ли камера, прежде чем начать урок.
прежде чем начинать урок (imperfective):
- can sound a bit more general / habitual / process-oriented:
  - “before (you) start / whenever you’re starting the lesson”
- often used in instructions or routines

In everyday speech, many speakers would naturally say прежде чем начать урок here. The given начинать variant is also correct; it just leans slightly toward a more general “before starting (in general)” feel.

Why is урок in this form? What case is it?

Урок here is in the accusative singular, functioning as the direct object of начинать (“to start”).

начинать что? – “to start what?” → урок

For inanimate masculine nouns like урок, the nominative and accusative forms are identical:

nominative: урок
accusative: урок

So the form looks the same, but functionally it is accusative as the object of начинать.

Could we say something like Проверь, включена ли камера, перед тем как начинать урок instead of прежде чем?

Yes. Перед тем как is another very common way to say “before (doing something).”

Проверь, включена ли камера, перед тем как начинать урок.
or: … перед тем, как начать урок.

Nuances:

прежде чем is a bit more compact and can feel slightly more “written” or literary, but is very common in speech too.
перед тем как is very natural in both spoken and written Russian, and often feels a bit more neutral-conversational.

Meaning-wise, here they’re essentially interchangeable.

Does Проверь sound rude? How do I make this more polite?

By itself, Проверь is a plain imperative, not automatically rude, but:

it can sound direct / commanding, depending on voice and context
with peers or friends, it’s normal
to a teacher, stranger, or in formal settings, it’s better to use вы-forms or add softeners

More polite options:

Проверь, пожалуйста, включена ли камера… – informal but polite (adding пожалуйста)
Проверьте, пожалуйста, включена ли камера, прежде чем начинать урок. – formal, polite

So the base sentence is neutral-informal. To make it clearly polite, add пожалуйста and/or use Проверьте with вы.