Refer to FIGURE 4.1 below of an inverting operational amplifier and answer the questions that follow - NSC Electrical Technology Electronics - Question 4 - 2023 - Paper 1

Operational amplifiers are rarely used in open-loop mode because they have very high gain. This can lead to instability, where even a small change in input results in a large and potentially saturating output. Open-loop operation can cause the op-amp to drive the output to its maximum voltage limits, making it impractical for most applications.

The voltage gain (Av) of an inverting operational amplifier is calculated using the formula:

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

In this case, substituting the values:

$A_v = -\frac{1.2k\Omega}{1k\Omega} = -1.2$

Thus, the voltage gain is -1.2, indicating a phase inversion.

1. Resistor R8 serves to set the input impedance of the operational amplifier circuit, which helps in minimizing the loading effect on the previous stage.

2. It acts as part of the feedback loop, contributing to the overall gain and stability of the amplifier by controlling the feedback levels.

For a non-inverting operational amplifier, the voltage gain (Av) can be calculated using the formula:

$A_v = 1 + \frac{R_F}{R_{in}}$

Given the values, we have:

$A_v = 1 + \frac{120k\Omega}{10k\Omega} = 1 + 12 = 13$

Therefore, the voltage gain of the circuit is 13.

1. Timer circuits for creating delays in applications such as digital wrist watches.

2. Oscillators for generating square waves in audio applications.

1. The 555 IC cannot handle very high currents or voltages, which limits its use in high-power applications.

2. It can be sensitive to fluctuations in power supply, potentially affecting the stability of its operation.

Pin 4 of the 555 IC is the Reset pin. It is used to reset the timer to its initial state. When this pin is grounded, it immediately resets the output, allowing the timer to start over or stop its current operation.

(a) The NPN transistor in the circuit acts as a switch or an amplifier. It allows the control of a larger current flow based on smaller input signals, effectively driving connected loads or interfacing with other components in the circuit.

(b) Comparator 2 is responsible for comparing the input voltage from the trigger pin against a reference voltage. It determines the output state of the timer based on this comparison, effectively determining whether the output should be high or low.