In the following, which one of the diodes is reverse biased?
(a) Option A
(b) Option B
(c) Option C

Q: What if there is a resistor in the circuit? Does it change the bias?

The resistor causes a voltage drop only if current is flowing. To determine the *initial* bias state, we look at the applied potentials. If the applied potential difference tries to push current from n to p, it's reverse biased, and no steady current flows, so the resistor doesn't drop any voltage.

Q: How do I treat the Ground symbol?

The Ground symbol simply acts as a reference point with a potential of exactly $0\text{ V}$. You can treat it just like a battery terminal connected to $0\text{ V}$.

Q: In option (b), both sides seem to be at negative or zero potential. How is it forward biased?

Forward bias doesn't require positive voltages; it only requires the p-side to be *more positive* (or less negative) than the n-side. Since $0\text{ V}$ is mathematically greater than $-10\text{ V}$, the p-side is at a higher potential, making it forward biased.

Q: Why does the diode in option (d) point upwards?

The orientation of the diode symbol tells you which side is p and which is n. The triangle points in the direction of forward current (from p to n). So, pointing upwards means the bottom is the p-side and the top is the n-side.

Q: Can a diode be neither forward nor reverse biased?

Yes, if the potential difference across the diode is exactly zero ($V_p = V_n$), it is unbiased. No net current flows in this state.

Question

In the following, which one of the diodes is reverse biased?

Options:

(A)

(B)

(C)

(D)

Sigma Percentile · Accepted Answer

### Identifying Reverse Biased Diodes: A Visual Guide

When dealing with p-n junction diodes in circuits, one of the most fundamental skills is determining whether the diode is forward biased or reverse biased. This simple check dictates whether the diode will act like a closed switch (allowing current to flow) or an open switch (blocking current).

To figure this out, we don't need to calculate the exact current. We just need to look at the electrical potentials applied to the two sides of the diode: the **p-side** (represented by the flat base of the triangle) and the **n-side** (represented by the straight line).

Think of electrical potential like the height of a hill. Current naturally wants to flow downhill, from a higher positive potential to a lower or negative potential.

- If the **p-side is at a higher potential** than the n-side ($V_p > V_n$), the diode is **forward biased**.
- If the **n-side is at a higher potential** than the p-side ($V_n > V_p$), the diode is **reverse biased**.

Let's apply this logic to the four circuits provided in the problem.

### Analyzing the Options

**Option (a):**
In this circuit, the p-side is directly connected to a $+10	ext{ V}$ source. The n-side is connected through a resistor to a $-12	ext{ V}$ source. Since $+10	ext{ V}$ is significantly higher than $-12	ext{ V}$, we have $V_p > V_n$. This diode is comfortably forward biased.

**Option (b):**
Here, the p-side is connected to the Ground symbol. Ground always represents exactly $0	ext{ V}$. The n-side is connected through a resistor to $-10	ext{ V}$. Comparing the two, $0	ext{ V}$ is greater than any negative number. Therefore, $V_p > V_n$, and this diode is also forward biased.

**Option (c):**
This circuit is functionally very similar to option (b). The p-side is grounded ($0	ext{ V}$), and the n-side is pulled towards $-10	ext{ V}$. Once again, the potential at the p-side is higher than the potential at the n-side. It is forward biased.

**Option (d):**
Now, let's look at the final circuit. The orientation of the diode is flipped. The n-side (the straight line) is connected through a resistor to a $+5	ext{ V}$ source. The p-side (the triangle base) is connected to Ground ($0	ext{ V}$).

In this scenario, the n-side is at a positive potential, while the p-side is at zero. This means $V_n > V_p$. The "hill" is tilted the wrong way for the diode, so it blocks the current. This perfectly satisfies the condition for **reverse bias**.

### Final Conclusion

By systematically checking the potentials $V_p$ and $V_n$ for each circuit, we found that only the diode in option (d) has a higher potential on its n-side. Thus, option (d) is the correct answer.

Animated Solution for Physics - Semiconductors: In the following, which one of the diodes is reverse biased?

Select Answer:

Visualized Solution

Concept of Biasing

Analyzing Option (a)

Analyzing Option (b)

Analyzing Option (c)

Analyzing Option (d)

Conclusion

The Sigma Insight: P-N Junction Diode

Identifying Reverse Biased Diodes

Analyzing the Options

Final Conclusion

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