IIT JEE Mains 2025: Solution of question 34 based on forward biased on junction diode in electronics

Hello viewers! Welcome back to our channel dedicated to mastering electronics and physics for competitive exams like JEE, NEET, CUET, and more.

Today’s topic is an important one – “Forward Biasing of Diodes” – explained using a multi-option circuit-based question.

We’ll not only solve the question but dive deep into:

What forward bias means,

How to identify it in a circuit,

Why it matters in real-world electronics.

By the end of this video, you will be able to confidently tackle any diode biasing question that appears in your exams.

Grab a notebook and let’s start!
What is a Diode?

A diode is a two-terminal semiconductor device that allows current to flow in one direction only – from the anode to the cathode.

Anode → Positive side (usually on the left in symbols)

Cathode → Negative side (marked with a line/bar)

🔌 Forward Bias vs. Reverse Bias
✅ Forward Bias:

The anode is at a higher potential than the cathode.

The PN junction conducts current.

The diode behaves like a closed switch.

❌ Reverse Bias:

The cathode is at a higher potential.

The diode does not conduct.

It behaves like an open switch.

Think of it like:

Forward bias = ON

Reverse bias = OFF

🧪 Real-Life Analogy:

Imagine a one-way valve in a pipe system. It only opens if the pressure is applied from one side. That’s how a forward-biased diode works!

Let’s analyze the question:

Q34. Which of the following circuits represents a forward biased diode?

We are given five circuit diagrams (A to E). In each, we must determine whether the diode is forward or reverse biased based on the given voltages.

We also have four multiple-choice options, which list combinations of correct answers.

Our goal is to:

Understand each diagram.

Determine whether the diode is forward or reverse biased.

Pick the correct combination from the options.

Tip 1: Use a Reference Point

Always compare anode vs cathode potential.

Doesn’t matter if both are negative or both are positive. It’s the relative voltage that matters.

💎 Tip 2: Think Current Direction

If current can flow from anode to cathode, the diode is ON.

If current is blocked, it’s OFF.

Common Student Mistakes

Assuming negative voltage = reverse bias. Not always true.

Ignoring relative potential difference.

Confusing ground (0 V) as always negative. It's just a reference point.

📱 Diodes in Circuits:

Rectifiers in power supplies

Clipping & clamping circuits

Protection in electronics

LEDs (Light Emitting Diodes)

Understanding biasing is crucial because:

Misbiased diodes don’t conduct → circuit malfunction

Proper biasing → correct output, safety, efficiency