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Picture of the circuit

I thought it would be through lamp 1 and 3 because the electrons can go through the circuit between lamp 2 and 3, then through lamp 3 then through the circuit between 2 and 3 again and finally down to the voltage area. However the correct answer is only through lamp 1.

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  • $\begingroup$ Have you checked which way current flows through a diode? $\endgroup$
    – Guy Inchbald
    Commented Jun 3, 2021 at 16:53

1 Answer 1

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A lamp will light up if there is a potential difference across it. The current can flow through the middle diode, so the potential in the top horizontal wire is the same as in the bottom horizontal wire, so the potential across lamp 2 and lamp 3 are both zero. The potential across lamp 1 is just the potential of the battery so it lights up.

EDIT: This assumes that the circuit components are ideal. A real diode has a small voltage drop across it which would mean a small voltage drop across lamp 2 so it might light up just a little.

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    $\begingroup$ This assumes that the diode is ideal and has zero resistance in the preferred direction. Otherwise there will be a small potential across lamp 2, but very little current flowing through it (because the lamp has way higher resistance than the diode). So it may light up a tiny bit. Lamp 1 will definitely light up though, and lamp 3 for sure will not light up. $\endgroup$
    – Arturo don Juan
    Commented Jun 3, 2021 at 17:21
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    $\begingroup$ This is true. I assumed based on the context of the question that we were considering ideal circuit components. Editing original post to include this $\endgroup$
    – Mia
    Commented Jun 3, 2021 at 18:36