Der eingeschaltete Fernseher ist zu laut.

Because eingeschaltet is being used like an adjective before a noun, and in German that kind of adjective must take an ending.

Here, Fernseher is:

• masculine
• singular
• nominative (it is the subject of the sentence)

The article der already marks the gender and case, so the adjective takes the weak ending -e:

• der eingeschaltete Fernseher

This works the same way as:

• der große Hund
• der alte Mann

So eingeschaltet becomes eingeschaltete because it stands before Fernseher.

It is the past participle of the verb einschalten used as an adjective.

• verb: einschalten = to switch on / turn on
• participle: eingeschaltet = switched on / turned on

In this sentence, it describes the noun:

• der eingeschaltete Fernseher = the switched-on TV

This is very common in German. Past participles are often used adjectivally:

• die geschlossene Tür = the closed door
• das geöffnete Fenster = the opened window

Because einschalten is a separable verb:

• prefix: ein-
• base verb: schalten

Its past participle is formed with ge inserted between the prefix and the base:

• einschalten → eingeschaltet

This is the normal pattern for many separable verbs:

• anmachen → angemacht
• aufmachen → aufgemacht
• einschlafen → eingeschlafen

So eingeschaltet is the standard participle form.

Yes. That is also correct, but it means something slightly different in structure.

• Der eingeschaltete Fernseher ist zu laut.

  • eingeschaltete describes Fernseher directly
  • literally: The switched-on TV is too loud

• Der Fernseher ist eingeschaltet.

  • eingeschaltet comes after ist
  • it is a predicate adjective
  • means: The TV is switched on

You can even combine them:

• Der Fernseher ist eingeschaltet und zu laut.

So the original sentence uses eingeschaltet before the noun to identify which TV or what state the TV is in.

Because zu means too.

• laut = loud
• zu laut = too loud

So:

• Der Fernseher ist laut. = The TV is loud.
• Der Fernseher ist zu laut. = The TV is too loud.

This is an important difference. Zu implies that the loudness is excessive or a problem.

Here, laut is an adjective used after the verb ist.

German often uses adjectives after sein without any ending:

• Der Fernseher ist laut.
• Das Haus ist groß.
• Die Kinder sind müde.

So although eingeschaltete needs an ending before the noun, laut does not need one after ist.

That is why you get:

• der eingeschaltete Fernseher but
• Der Fernseher ist zu laut

Because all nouns in German are capitalized.

So:

• der Fernseher = the television set
• laut = not capitalized, because it is an adjective
• eingeschaltete = not capitalized here, because it is functioning as an adjective

This is one of the most consistent spelling rules in German.

Because German main clauses normally follow the verb-second rule.

In this sentence:

• Der eingeschaltete Fernseher = position 1
• ist = position 2
• zu laut = the rest

So the basic structure is:

• Subject + verb + complement

If you move something else to the front, the verb still stays second:

• Heute ist der eingeschaltete Fernseher zu laut.

That verb-second pattern is a central feature of German word order.

Yes, very often.

• Der Fernseher ist an. = The TV is on.
• Der Fernseher ist eingeschaltet. = The TV is switched on.

In many everyday situations, an is more natural and conversational.

However, before a noun, you usually cannot use an the same way:

• der an Fernseher ❌

So if you want to say the switched-on TV before the noun, eingeschaltet works well:

• der eingeschaltete Fernseher

Fernseher means the television set / TV.

That is different from:

• das Fernsehen = television as a medium, or watching TV

So:

• Der Fernseher ist zu laut. = The TV set is too loud.
• Ich sehe gern fern. = I like watching TV.

English uses TV for both ideas, but German often separates them more clearly.

Not quite.

• der laute Fernseher = the loud TV
• der eingeschaltete Fernseher = the switched-on TV

In the original sentence, eingeschaltete tells you the TV is on, and zu laut tells you it is too loud.

So:

• Der eingeschaltete Fernseher ist zu laut.

contains two different ideas:

1. the TV is switched on
2. it is too loud

If you said:

• Der laute Fernseher ist zu laut

that would sound odd, because you would basically be saying the loud TV is too loud.