Learn Hardcore Korean: gaeksil nae jeonwon seuwichireul kkeumyeon baeteori somoga jureodeureoyo. - If you turn off the power switch in the room, battery drain decreases.

객실 내 means “inside the guest room,” using the bound noun 내(內) “inside/within.” It’s formal and common on signs or manuals. 객실 안에 is the everyday way to say “in the room.” Both are correct; the tone/register differs. Here, 객실 내 전원 스위치 means “the power switch in the room” as one noun phrase.

Why isn’t there a particle after “객실 내”? Shouldn’t it be “객실 내에서”?

Because 객실 내 is modifying the following noun (전원 스위치) to form “the power switch in the room.” No particle is needed inside a noun phrase. If you want to mark the location of the action, you can say 객실 내에서 전원 스위치를 끄면…

Why use “전원 스위치” instead of just “전원”? Are both correct?

전원 스위치 refers to the physical switch (e.g., a master switch in a hotel room).
전원을 끄다 (“turn off the power”) is also natural. 객실 내 전원을 끄면… is correct too.
Use 스위치 when you want to emphasize the physical control; 전원 is more general.

What does the object marker -를/-을 do in “스위치를”?

It marks 전원 스위치 as the direct object of 끄다 (“to turn off”): you are turning off the switch.

How does the conditional -(으)면 work in “끄면”? Does it mean “if” or “when”?

-면 attaches to verb stems and can mean “if” or “when/whenever,” depending on context. 끄- + 면 → 끄면. Here it’s a general condition: “If/when you turn off…, battery drain decreases.”

How do I conjugate “끄다”? I’m confused by “끄면” vs “꺼요.”

Dictionary: 끄다
Polite present: 꺼요 (끄 + 어요 → 꺼요)
Past: 껐어요
If/when: 끄면 (no vowel change before -면)
Please turn it off: 꺼 주세요 / 꺼 주시겠어요?
Intransitive “it goes off”: 꺼지다 → 꺼져요

What’s the difference between “끄다,” “꺼지다,” and “켜다”?

끄다: transitive “turn off/put out” (불을 끄다, 전원을 끄다).
꺼지다: intransitive/passive “be turned off/go out” (불이 꺼지다).
켜다: “turn on” (전등을 켜다, 전원을 켜다).

Why “배터리 소모가 줄어들어요” instead of just “줄어요”?

줄다 and 줄어들다 both mean “decrease.” 줄어들다 often feels more descriptive or gradual and is common in neutral/formal writing. 배터리 소모가 줄어요 is also fine; 줄어들다 just sounds a bit more formal/technical here.

Can I say “배터리가 줄어들어요” instead?

People do say it, but it’s clearer to specify what’s decreasing:

배터리 잔량이 줄어들어요 (“the remaining battery level goes down”), or
Keep the original: 배터리 소모가 줄어들어요 (“battery consumption/drain decreases”).
배터리가 줄어들어요 is understandable but less precise.

Why is it “배터리 소모가” with 가 and not “배터리 소모는”?

가/이 marks the subject and presents neutral/new information: “battery drain decreases.”
는/은 marks a topic/contrast: 배터리 소모는 줄어들어요 implies “As for battery drain, it decreases (but something else may not).”

Is politeness only at the end? Why isn’t “끄면” polite too?

Yes. In Korean, subordinate clauses (like conditionals with -면) don’t carry politeness. The final verb 줄어들어요 sets the politeness for the whole sentence.

Can I change the word order or placement of the location phrase?

Yes. Natural variations include:

객실 내 전원 스위치를 끄면 배터리 소모가 줄어들어요. (original)
객실 내에서 전원 스위치를 끄면 배터리 소모가 줄어들어요. (emphasizes place of action)
전원 스위치를 객실 내에서 끄면 배터리 소모가 줄어들어요.
Korean word order is flexible if particles are correct and the main verb is last.

Do I need a plural marker like “전원 스위치들”?

No. Korean usually omits 들 unless you need to emphasize “multiple.” 전원 스위치를 can mean one or all relevant switches based on context.

Is “배터리 소모” natural? Any synonyms I could use?

Yes, it’s natural. Alternatives:

배터리 소모량 (amount of battery drain)
배터리 사용량 (amount of battery use)
전력 소모 (power consumption; more technical)
Choose based on what you want to emphasize.

How do I say “If you turn it off and keep it off, …”?

Use -아/어 놓다 to express leaving it in that state:

전원 스위치를 꺼 놓으면 배터리 소모가 줄어들어요.

What’s a more formal version suitable for a notice/sign?

객실 내 전원 스위치를 끄면 배터리 소모가 줄어듭니다.
The -습니다 style is standard on signs and instructions.

Why “객실” and not “방”?

객실 is the formal term for a guest room (hotels, accommodations). 방 is the general, casual word for “room.” For signage or instructions, 객실 is preferred.

Any quick pronunciation tips for key words?

끄면: kkeu-myeon [k͈ɯ.mjʌn] (tense kk; ㅡ as close central unrounded vowel).
줄어들어요: ju-reo-deu-reo-yo [t͡ɕu.ɾʌ.dɯ.ɾʌ.jo].
Say 스위치를 끄면 smoothly without pausing between words.