What does the thermal noise generated by a resistor depend upon?

Introduction / Context:
Quantifying resistor noise helps engineers choose components for preamplifiers, mixers, and precision measurement equipment. Thermal noise is an unavoidable physical phenomenon.

Given Data / Assumptions:

• Resistor with value R operating at absolute temperature T.
• Observation bandwidth B.
• No additional excess noise mechanisms (e.g., flicker).

Concept / Approach:

The mean-square thermal noise voltage across a resistor is v_n^2 = 4kTRB. Thus, thermal noise magnitude increases with both resistance R and absolute temperature T, and also with bandwidth B.

Step-by-Step Solution:

Verification / Alternative check:

Practical lab measurements show doubling the resistance or doubling the absolute temperature increases the noise voltage accordingly (by sqrt(2) in RMS for each doubling).

Why Other Options Are Wrong:

• Only R or only T: incomplete; both contribute.
• Neither: contradicts physics.
• Only DC voltage: thermal noise exists even with zero DC bias.

Common Pitfalls:

• Ignoring the bandwidth term B, which also scales noise.

Final Answer:

Both its resistance value and its operating temperature