Question Video: Determining Whether a PN Junction is Forward Biased or Reverse Biased Physics • 9th Grade

The diagram shows a PN junction in a circuit. The positively charged side of the junction’s depletion region is shown in red, and the negatively charged side is shown in blue. Is the junction forward biased or reverse biased?

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Video Transcript

The diagram shows a PN junction in a circuit. The positively charged side of the junction’s depletion region is shown in red, and the negatively charged side is shown in blue. Is the junction forward biased or reverse biased?

The question asks us to determine whether, in the diagram, the PN junction is forward biased or reverse biased. First, let’s remember some important aspects of a PN junction connected to a power supply in an electrical circuit.

There are two possible ways to connect the junction to a power supply: forward biased, where the positive terminal of the power supply is connected to the P-type side, while the negative terminal is connected to the N-type side, or reverse biased, where the negative terminal of the power supply is connected to the P-type side and the positive terminal is connected to the N-type side.

Looking at our diagram, we can see that there is a net positive charge on the left-hand side of the depletion region and a net negative charge on the right-hand side of the depletion region. The side of the junction that has net positive charge around the depletion region is the N-type side. The side of the junction that has net negative charge around the depletion region is the P-type side.

We can see then that the positive terminal of the power supply connects to the N-type side of the junction. And the negative terminal of the power supply connects to the P-type side of the junction. The junction is therefore reverse biased.

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