Prøvelinsen passer til brilleseddelen.

Because both nouns are in the definite singular form in Bokmål.

• en prøvelinse = a trial lens

• prøvelinsen = the trial lens

• en brilleseddel = an eyeglass prescription / glasses prescription note
• brilleseddelen = the eyeglass prescription

For many masculine nouns in Norwegian, the definite singular ending is -en.

The basic forms are:

• prøvelinse
• brilleseddel

In the sentence, they appear as:

• prøvelinsen = definite singular
• brilleseddelen = definite singular

Both are also compound nouns, which is very common in Norwegian.

• prøve
  • linse → prøvelinse
• brille
  • seddel → brilleseddel

So Norwegian often combines smaller words into one longer noun where English might use a phrase.

Here, passer til means something like:

• fits
• matches
• corresponds to
• is suitable for

So the idea is that the trial lens is the right one for the eyeglass prescription.

The verb is passe, and with til it often means to fit/match/be appropriate for something.

Examples:

• Denne fargen passer til jakka. = This color goes with the jacket.
• Brillene passer til ansiktet ditt. = The glasses suit your face.

In your sentence, it is not mainly about physically fitting into something, but about being the correct match.

Because Norwegian often uses passe til when talking about matching or being suitable for something.

English and Norwegian do not always use the same preposition, so this is something you mostly have to learn as a set expression:

• å passe til noe = to fit/match something

You should think of passer til as a unit here, not translate it word-for-word.

Because Norwegian verbs do not change for person or number the way English verbs do.

In English:

• I fit
• he fits
• they fit

In Norwegian present tense, the verb stays the same:

• jeg passer
• han passer
• de passer

So passer is simply the present tense of å passe.

No, this is a very normal Norwegian main clause:

• Prøvelinsen = subject
• passer = verb
• til brilleseddelen = prepositional phrase

So the pattern is basically:

Subject + Verb + Other information

This is the standard word order in a simple statement.

Yes, in many contexts you can.

The noun linse is feminine in Norwegian, and in Bokmål many feminine nouns can either:

• take common gender / masculine-style forms: en linse – linsen
• or take feminine forms: ei linse – linsa

So both of these can be correct in Bokmål, depending on style and preference:

• Prøvelinsen passer til brilleseddelen.
• Prøvelinsa passer til brilleseddelen.

The version with -en is very common and fully correct.

Because Norwegian usually writes compound nouns as one word.

So:

• brille
  • seddel → brilleseddel

This is different from English, where similar ideas are often written as separate words, such as glasses prescription or prescription note.

A very useful rule for learners is: If English has a noun + noun combination, Norwegian often turns it into one compound noun.

Yes, literally it is something like glasses note/slip, but in real use it refers to the eyeglass prescription or the written prescription information for glasses.

This is a good example of why literal translation is not always the best way to understand a Norwegian compound. The parts help you recognize the word, but the whole compound has its own practical meaning.

Yes, at least slightly.

Compare:

• Prøvelinsen passer til brilleseddelen.

  • The trial lens matches the prescription.
  • This sounds like a specific lens and a specific prescription.

• En prøvelinse passer til en brilleseddel.

  • A trial lens matches a prescription.
  • This sounds more general or less specific.

So the definite forms in your sentence suggest that both things are already known in the context.

A rough guide is:

PRØ-ve-lin-sen PAS-ser til BRIL-le-sed-de-len

A few useful points:

• ø is not like a normal English vowel, so it may need practice.
• r in Norwegian is usually clearly pronounced.
• The compounds keep a natural stress pattern, often with strong stress near the beginning of each compound:
  • PRØvelinsen
  • BRILleseddelen

You do not need perfect pronunciation to understand the grammar, but recognizing the compounds as single words is very helpful when listening.