Когда прозвучит звонок, урок закончится.

When the bell rings, the lesson will end.

Breakdown of Когда прозвучит звонок, урок закончится.

• когда: when
• урок: the lesson
• звонок: the bell
• закончиться: to end

Questions & Answers about Когда прозвучит звонок, урок закончится.

Why are both verbs in the future: прозвучит and закончится?

Because Russian usually uses the future in both parts when it is talking about a future event.

In English, we say:

• When the bell rings, the lesson will end.

So English uses a present form (rings) after when.
Russian does not do that here. Russian says, literally:

• When the bell will ring, the lesson will end.

That is why you get:

• Когда прозвучит звонок, урок закончится.

This is completely normal Russian grammar.

Why are прозвучит and закончится perfective verbs?

They are perfective because the sentence refers to single completed events:

• the bell will sound / ring once
• the lesson will come to an end

Perfective verbs in Russian often express:

• a one-time event
• a completed result
• a change from one state to another

Here:

• прозвучит = will sound / will ring out
• закончится = will end / will be over

If you used imperfective forms instead, the meaning would change and would usually suggest an ongoing, repeated, or habitual action.

Why is it Когда прозвучит... and not something like ?