(d)

Figure $20

Question

(d)

Figure $20 < 1$

-Refer to Figure 20-1 (a). If $\mathrm { R } _ { 1 } = \mathrm { R } _ { 2 } = 30 \mathrm { k \Omega }$ and the closed loop gain is 450 , the value of the external gain-setting resistor $R _ { G }$ is:
A) $134 \mathrm { k } \Omega$ 
B) $13.4 \Omega$ 
C) $134 \Omega$ 
D) none of the above.

Quizplus · Accepted Answer

Using the formula for closed loop gain of an inverting amplifier, we have: 
\begin{equation}
A_{CL} = -\frac{R_F}{R_G} = 450
\end{equation}
Since $R_1 = R_2$, the feedback resistor ($R_F$) is equal to $2R_1$, or 60 k$\Omega$. Plugging this in to the equation, we get:
\begin{equation}
450 = -\frac{60 \mathrm{k}\Omega}{R_G}
\end{equation}
Solving for $R_G$ gives us $R_G = \frac{60 \mathrm{k}\Omega}{450} = 133.3 \Omega$, which is closest to choice C ($134 \Omega$). Therefore, the best choice is C.

(D) Figure 20<120 < 120<1 -Refer to Figure 20-1 (A) R1=R2=30kΩ\mathrm { R } _ { 1 } = \mathrm { R } _ { 2 } = 30 \mathrm { k \Omega }R1​=R2​=30kΩ

(D)

Figure $20 < 1$ -Refer to Figure 20-1 (A) $\mathrm { R } _ { 1 } = \mathrm { R } _ { 2 } = 30 \mathrm { k \Omega }$