Your question is One-Entry Light Bulb Puzzle. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You have one sealed room with one light bulb and one door, and three switches outside. You can enter the room only once to see whether the bulb is lighting. How do you determine the correct switch?