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(R₁ + R₂) KTB}
= √{4(20* 10³ + 30*10³) * 1.381×10^-23 * 293* 10*10³ }
= 284.48 * 10^-7