Figure $18

Question

Figure $18 < 1$
-If $\mathrm { R } _ { f } = 100 \mathrm { k } \Omega$ and $\mathrm { R } _ { \mathrm { i } } = 6.8 \mathrm { k } \Omega$ in Figure 18-1(c), the voltage gain equals__________
A) -15.7 
B) -1 
C) -14.7 
D) infinite

Quizplus · Accepted Answer

The voltage gain of the non-inverting amplifier can be calculated using the formula:

$$\mathrm{A} = 1 + \frac{\mathrm{R_f}}{\mathrm{R_i}}$$

Substituting the given values, we get:

$$\mathrm{A} = 1 + \frac{100\mathrm{k}\Omega}{6.8\mathrm{k}\Omega} = 15.71$$

Since the input is applied to the non-inverting terminal, the output is in phase with the input, and the gain is positive. However, the question asks for the voltage gain in dB, which is given by:

$$\mathrm{A_{dB}} = 20\log_{10}(\mathrm{A})$$

Substituting the value of A, we get:

$$\mathrm{A_{dB}} = 20\log_{10}(15.71) \approx 24\mathrm{dB}$$

Since the gain is positive, the correct answer is the option with the negative value in dB. Hence, the answer is C (-14.7).

Figure 18<118 < 118<1 -If Rf=100kΩ\mathrm { R } _ { f } = 100 \mathrm { k } \OmegaRf​=100kΩ

Figure $18 < 1$ -If $\mathrm { R } _ { f } = 100 \mathrm { k } \Omega$