# Calculation of thermal noise when resistors are connected in series

**Q21. At a room temperature of 293K, calculate the thermal noise generated by two resistors of 20KΩ and 30 KΩ when the bandwidth is 10 KHz and the resistors are connected in series.**

**Option: **

300.66* 10^{-7}

284.48 * 10^{-7}

684.51 * 10^{-15}

106.22 * 10^{-7}

**Explanation:**

Noise voltage V_{n}= √(4R KTB)

Where, K = 1.381×10^{-23} J/K, joules per Kelvin, the Boltzmann constant

B is the bandwidth at which the power P_{n} is delivered.

T noise temperature

R is the resistance

Noise voltage by resistors when connected in series is

V_{n}= √{4(R_{1} + R_{2}) KTB}

= √{4(20* 10^{3} + 30*10^{3}) * 1.381×10^{-23} * 293* 10*10^{3} }

= 284.48 * 10^{-7}