---
title: "Diode circuit current, eta 1.74, 10 V"
subject: "Electronics Devices and Circuit"
chapter: 1
key: "semester_3/electronics_devices_and_circuit:diode-current-eta-1p74-10v"
source: https://www.bctengineer.com/q/semester_3/electronics_devices_and_circuit/diode-current-eta-1p74-10v
site: BCT Engineering
---

# Diode circuit current, eta 1.74, 10 V

Electronics Devices and Circuit · Chapter 1: Diodes

- Asked in: 2072 Chaitra, 4 marks
- Video: [Diode Current Equation || Lecture 10 Electronic Devices & Circuit || Explained in Urdu / Hindi](https://www.youtube.com/watch?v=uwg1sZuMPYQ) — Tuition Point
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electronics_devices_and_circuit/diode-current-eta-1p74-10v
- Whole chapter: https://www.bctengineer.com/md/semester_3/electronics_devices_and_circuit/chapter-1

## Question

In the given circuit, the diode used has its η = 1.74 and it conducts 1mA at forward bias voltage of 0.7 V. Find the current flow in the circuit.
[Figure: V = 10 V source in series with R = 500 Ω and a diode, current ID = ?]

## Short answer

Iteration with VD=0.7+0.0435 ln(ID/1mA) and ID=(10−VD)/500 gives VD≈0.827 V, ID≈18.35 mA.

## Answer

Use the diode's exponential law and KVL, and iterate.

#### Given
V = 10 V, R = 500 Ω, η = 1.74, ID = 1 mA at 0.7 V, VT = 25 mV, so η VT = 43.5 mV.

#### Equations
```text
VD = 0.7 + 0.0435 ln(ID / 1 mA)
ID = (10 - VD)/500
```

#### Iteration
| Step | VD guess (V) | ID (mA) | New VD (V) |
|---|---|---|---|
| 1 | 0.700 | 18.600 | 0.8272 |
| 2 | 0.8272 | 18.346 | 0.8266 |
| 3 | 0.8266 | 18.347 | 0.8266 |

Converged at VD = 0.8266 V.

```text
ID = (10 - 0.8266)/500 = 18.35 mA
```

**Answer: I ≈ 18.35 mA** (VD ≈ 0.83 V). The constant-drop (0.7 V) estimate would be 18.6 mA, close to this value.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which pair of equations is solved?
   A. VD = 0.7 + 10 ID and ID = VD/500
   B. VD = 10 - ID and ID = 0.7/500
   C. VD = 0.7 + 0.0435 ln(ID/1 mA) and ID = (10 - VD)/500
   D. VD = 0.0435 ID and ID = 10/500
   Answer: C. The diode law and KVL are combined by iteration. (Key point: Equations)

2. What is eta VT?
   A. 43.5 mV
   B. 25 mV
   C. 1.74 V
   D. 14.4 mV
   Answer: A. 1.74 x 25 mV = 43.5 mV. (Key point: eta VT)

3. From VD = 0.7 V, what is ID?
   A. 20 mA
   B. 18.6 mA
   C. 9.3 mA
   D. 1 mA
   Answer: B. ID = (10 - 0.7)/500 = 18.6 mA. (Key point: First iteration)

4. What is the converged current?
   A. About 1.8 mA
   B. 10 mA
   C. 18.6 mA
   D. About 18.3 mA
   Answer: D. VD = 0.8266 V gives ID = 18.35 mA. (Key point: Final current)

## Close variants set in other exams

- [Diode circuit current, eta 1.74, 6 V](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Adiode-current-eta-1p74-6v) — Electronics Devices and Circuit, chapter 1, asked 4×
- [Diode circuit current, eta 1.74](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Adiode-current-eta-1p74) — Electronics Devices and Circuit, chapter 1, asked 4×

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