Topic: Communication Systems
The thermal noise spectral density generated in a resistor kept at $t^{\circ}C$ is given by
- A. $k(t+273)$
- B. $ktB$
- C. $k(t+273)B$
- D. $2k(t+273)$
Answer: A. $k(t+273)$
Explanation: Thermal noise power is $P_n = kTB$. The thermal noise power spectral density is the ratio of thermal noise power to bandwidth, which is $P_n/B = kT$ Watts/Hz. Converting temperature from Celsius to Kelvin gives $T = (t+273)$ K. Therefore, the spectral density is $k(t+273)$.