Đáp án:
Giải thích các bước giải:
$B_1 = \dfrac{I}{R_1}.2.10^{-7} \Rightarrow R_1 = \dfrac{I.2.10^{-7}}{B_1}$
$B_2 = \dfrac{I}{R_2}.2.10^{-7} \Rightarrow R_2 = \dfrac{I.2.10^{-7}}{B_2}$
Ta có :
$R_E = \dfrac{R_1 + R_2}{2} = \dfrac{1}{2}I.2.10^{-7}(\dfrac{1}{B_1} + \dfrac{1}{B_2})$
Suy ra:
$B_E = \dfrac{I.2.10^{-7}}{R_E} = \dfrac{I.2.10^{-7} }{ \dfrac{1}{2}.I.2.10^{-7} .(\dfrac{1}{B_1}+\dfrac{1}{B_2} )}$
$= \dfrac{2}{\dfrac{1}{B_1} + \dfrac{1}{B_2}} = \dfrac{2B_1B_2}{B_1+B_2}$