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Question #43897

Difficulty: 8/10 | 🟢 Free

The Question

A circuit consists of a variable DC voltage source $V_0$ , a resistor $R = 40 \ \Omega$ , and a special avalanche diode connected in series. The diode is reverse-biased. The diode exhibits a 'snap-back' breakdown characteristic analogous to the transition from static to kinetic friction. It conducts zero current until the voltage across it reaches a static breakdown threshold $V_{BR} = 120 \text{ V}$ . Immediately upon reaching $V_{BR}$ , the diode breaks down and its voltage-current relationship discontinuously shifts to a dynamic state given by $V_D = V_H + I r_d$ , where $V_H = 70 \text{ V}$ is the holding voltage, $r_d = 10 \ \Omega$ is the dynamic resistance, and $I$ is the current. If the source voltage $V_0$ is slowly increased from zero, what is the power dissipated in the diode immediately after the breakdown occurs?

Options

A.
$80 \text{ W}$
B.
$120 \text{ W}$
C.
$87.5 \text{ W}$
D.
$40 \text{ W}$

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Variable_Constraint

Develop pure symbolic logic skills by mastering algebraic constraints without relying on numerical data.

Concepts Behind This Question

Zener vs Avalanche Breakdown|Dynamic Resistance|Kinetic Friction Transition

Why This Question Is Tricky

Common Mistakes

This question tests the student's ability to distinguish between a threshold condition (analogous to maximum static friction) and a dynamic operating condition (analogous to kinetic friction) in a circuit context.

A common misconception is to calculate the power dissipation using the static breakdown voltage $V_{BR}$ ( $P = V_{BR} \times I = 120 \text{ W}$ ), failing to recognize that the voltage across the device discontinuously 'snaps back' to a lower value $V_D = 80 \text{ V}$ once conduction begins.

Another trap is ignoring the dynamic resistance $r_d$ and treating the holding voltage $V_H$ as the only voltage drop, leading to an incorrect current and power ( $87.5 \text{ W}$ ).

The analogy enforces the concept that energy dissipation in the dynamic state depends strictly on the kinetic/dynamic parameters, not the static threshold.

Quick Facts About This Question

Question Information

Subject	Physics
Chapter	Semiconductor Electronics: Materials, Devices, and Simple Circuits - Class 12
Concept	Zener vs Avalanche Breakdown
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free