7.1 Explain what an operational amplifier (op amp) is - NSC Electrical Technology Power Systems - Question 7 - 2017 - Paper 1

The voltage gain for an inverting amplifier is given by the same formula used for the output voltage, but expressed in terms of gain:

$A_v = -\frac{R_f}{R_{in}}$

Substituting the given resistor values:

$A_v = -\frac{170000}{10000} = -17$

Thus, the gain of the amplifier is -17.

Using the inverting amplifier formula again:

$V_{OUT} = -V_{IN} \times \frac{R_f}{R_{in}}$

Given:

• $V_{IN} = 5V$
• $R_f = 200 k\Omega$
• $R_{in} = 20 k\Omega$

Calculating:

$V_{OUT} = -5V \times \frac{200000}{20000} = -50V$

Therefore, the output voltage is -50V.

Using the gain formula:

$A_v = -\frac{R_f}{R_{in}}$

Substituting the known values:

$A_v = -\frac{200000}{20000} = -10$

Thus, the gain of the amplifier is -10.

A Schmidt trigger can be used in signal conditioning to clean noisy signals, providing a stable digital output.

To calculate the resonant frequency $f$ of a Hartley oscillator, we use:

$f = \frac{1}{2\pi \sqrt{L_{T}C}}$

Where:

• $L_T = 27 mH$
• $C = 47 \mu F$

Calculating:

$f = \frac{1}{2\pi \sqrt{(27 \times 10^{-3}) \times (47 \times 10^{-6})}} \approx 141.28 Hz$

So, the resonant frequency is approximately 141.28 Hz.

For the RC phase-shift oscillator:

$f = \frac{1}{2\pi RC}$

Given:

• $R = 25 k\Omega$
• $C = 45 \mu F$

Calculating:

$f = \frac{1}{2\pi (25 \times 10^3)(45 \times 10^{-6})} \approx 57.76 kHz$

Thus, the resonant frequency is approximately 57.76 kHz.