---
title: "Find RB and RC for given IC, VCE"
subject: "Basic Electronics Engineering"
chapter: 3
key: "semester_2/basic_electronics_engineering:find-rb-rc-ic-1-2ma"
source: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/find-rb-rc-ic-1-2ma
site: BCT Engineering
---

# Find RB and RC for given IC, VCE

Basic Electronics Engineering · Chapter 3: Transistor

- Asked in: 2067 Chaitra, 4 marks
- Video: [[Solved]- Numerical for a BJT (Ib, Ic, Vce & Vcb =? )](https://www.youtube.com/watch?v=gu_FYvL5zc4) — Electronics Circuit Hub
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/find-rb-rc-ic-1-2ma
- Whole chapter: https://www.bctengineer.com/md/semester_2/basic_electronics_engineering/chapter-3

## Question

Find RB and RC in the given circuit. Given data are: IC = 1.2 mA, VCE = 6 V and β = 100. [Figure: +12 V supply; RC from supply to collector; RB from collector to base (collector feedback bias); emitter grounded; β = 100.]

## Short answer

IB = 12 µA. RC = (12−6)/(1.2m+12µ) ≈ 4.95 kΩ. RB = (6−0.7)/12µ ≈ 442 kΩ.

## Answer

**Given:** VCC = 12 V, IC = 1.2 mA, VCE = 6 V, β = 100. RB is connected from the collector to the base (collector feedback bias). Assume VBE = 0.7 V.

```text
        +12 V
          |
        [RC]
          |
          +-------+
          |       |
        [RB]      |C
          |     B |/
          +-------|  NPN
                  |\E
                  GND
```

#### Base current
IB = IC/β = 1.2 mA/100 = 12 µA

#### RC
The current through RC is IC + IB = 1.2 mA + 0.012 mA = 1.212 mA.

RC = (VCC − VCE)/(IC + IB) = (12 − 6)/1.212 mA = 4.95 kΩ

(With IC + IB ≈ IC, RC ≈ 6/1.2 mA = 5 kΩ.)

#### RB
KVL: VCE = IB RB + VBE

RB = (VCE − VBE)/IB = (6 − 0.7)/12 µA = 5.3/12 µA = 441.7 kΩ

**Answer: RC ≈ 4.95 kΩ (about 5 kΩ), RB ≈ 442 kΩ**

## Check yourself

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

1. With IC = 1.2 mA and β = 100, what is IB?
   A. 120 µA
   B. 12 µA
   C. 1.2 µA
   D. 0.12 mA
   Answer: B. IB = IC/β = 1.2 mA/100 = 12 µA. (Key point: Base current)

2. What current flows through RC in collector feedback bias, and what is RC?
   A. IC only; RC = 6 kΩ
   B. IC + IB = 1.212 mA; RC ≈ 4.95 kΩ
   C. IB only; RC = 500 kΩ
   D. IE = 0; RC is infinite
   Answer: B. RC carries both IC and IB: RC = (12 - 6)/1.212 mA = 4.95 kΩ, about 5 kΩ. (Key point: Finding RC)

3. Which relation gives RB?
   A. RB = (VCC - VBE)/IB
   B. RB = (VCE - VBE)/IB
   C. RB = VCE/IC
   D. RB = VBE/IB
   Answer: B. RB goes from collector to base, so VCE = IB RB + VBE and RB = 5.3/12 µA ≈ 442 kΩ. (Key point: Finding RB)

## Related in Basic Electronics Engineering

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