Noise in resistors: What is the type of noise generated due to random thermal agitation of charge carriers in a resistor?
Electronics and Communication Engineering
Radio Receivers
Difficulty: Easy
Choose an option
Answer
Correct Answer: Thermal noise
Explanation
Introduction / Context:Noise is an unavoidable phenomenon in electronic circuits. Resistors generate a specific type of noise due to the random motion of electrons caused by thermal energy.
Given Data / Assumptions:
- Resistor at a finite temperature T.
- Noise voltage measured across its terminals.
Concept / Approach:
Thermal noise, also called Johnson or Nyquist noise, is proportional to the resistor value, temperature, and measurement bandwidth. Its power spectral density is uniform (white) over practical frequency ranges.
Step-by-Step Solution:
Formula: Vn_rms = √(4 * k * T * R * B).Here, k = Boltzmann constant, T = absolute temperature (K), R = resistance (Ω), B = bandwidth (Hz).Thus, noise is purely thermal in nature.Verification / Alternative check:
Noise spectrum of a resistor shows flat (white) characteristic, confirming thermal noise is the correct answer.
Why Other Options Are Wrong:
- Partition noise: occurs in current division at semiconductor junctions.
- White noise: describes spectrum shape, but specific origin here is thermal.
- Shot noise: occurs in semiconductor diodes and vacuum tubes.
- Impulse noise: external transient disturbances, not inherent to resistors.
Common Pitfalls:
- Confusing white noise with thermal noise; while thermal noise is white, the correct physical term here is thermal noise.
Final Answer:
Thermal noise.