التيار الكهربائي ضعيف جدا.

In Arabic, the verb to be is usually not expressed in the present tense.

So:

• التيار الكهربائي ضعيف جدا
• literally: the electric current very weak
• naturally: The electric current is very weak

This is called a nominal sentence in Arabic.
If you wanted was, will be, etc., Arabic would usually use an actual verb.

التيار الكهربائي is one unit: the electric current.

The sentence divides like this:

• التيار الكهربائي = the subject
• ضعيف جدا = the predicate/comment about it

So الكهربائي is not saying the current is electrical as a separate statement. It is part of the noun phrase electric current.

Because in Arabic, adjectives normally come after the noun they describe.

So:

• التيار الكهربائي
• literally: the current electrical
• naturally: the electric current

This is the normal Arabic order:

• noun first
• adjective second

Because Arabic adjectives must agree with the noun they describe in definiteness as well as gender, number, and case.

Here:

• التيار = the current
• الكهربائي = the electrical / electric

Together they mean the electric current.

Compare:

• تيار كهربائي = an electric current / electric current
• التيار الكهربائي = the electric current

So if the noun is definite, the adjective must also be definite.

Because ت is a sun letter.

When ال comes before a sun letter, the l sound is not pronounced. Instead, the following consonant is doubled.

So:

• written: التيار
• pronounced: at-tayyār

But the spelling stays the same.

This is a very common feature of Arabic pronunciation.

It is pronounced approximately:

al-kahrabā’ī or more carefully al-kahrabā’iyy

A few useful points:

• ك is a moon letter, so the l in ال is pronounced here.
• The word comes from كهرباء (electricity).
• The ending -ي here makes it an adjective meaning electric / electrical.

So:

• التيار الكهربائي
• pronounced roughly: at-tayyār al-kahrabā’ī

Because it agrees with التيار, which is masculine singular.

Arabic adjectives agree with the noun in:

• gender
• number
• definiteness
• case

So:

• التيار = masculine singular
• ضعيف = masculine singular

If the noun were feminine, you would usually use:

• ضعيفة

For example:

• الإشارة ضعيفة = The signal is weak

جدا means very.

In Arabic, جدا usually comes after the adjective or adverb it intensifies.

So:

• ضعيف جدا = very weak
• literally: weak very

This is normal Arabic word order.

In fully vowelled writing, you may also see it as جِدًّا.

A fully vowelled version could be:

التَّيَّارُ الكَهْرَبَائِيُّ ضَعِيفٌ جِدًّا

These endings show grammatical case:

• التَّيَّارُ = subject, so it takes -u
• الكَهْرَبَائِيُّ = adjective matching the subject
• ضَعِيفٌ = predicate, usually indefinite with -un
• جِدًّا = very

In everyday writing, these short vowels are usually omitted:

التيار الكهربائي ضعيف جدا

Yes, but that is a different sentence.

• التيار الكهربائي ضعيف جدا = The electric current is very weak
• الكهرباء ضعيفة جدا = The electricity is very weak / The power is very weak

The second sentence uses الكهرباء (electricity), which is treated as feminine, so the adjective becomes:

• ضعيفة instead of ضعيف

So both are possible, but they are not exactly the same in wording or nuance.

In many contexts, it can correspond to either electric or electrical in English.

Here, التيار الكهربائي is the standard expression for electric current.

So even though electrical current is understandable in English, electric current is the more natural translation of this phrase.

In short:

• الكهربائي is an adjective related to electricity
• the best English translation depends on the noun it modifies
• with تيار, the normal translation is electric current