Refer to FIGURE 3.1 below and answer the questions that follow - NSC Electrical Technology Digital - Question 3 - 2020 - Paper 1

The op-amp is suitable for amplifying AC voltages due to its dual power supply configuration, which allows it to amplify both positive and negative halves of the AC signal. This enables the output to rise and fall above and below zero volts effectively, making it ideal for processing AC signals.

Point X is referred to as virtual ground because both inputs of the op-amp have the same potential, while the non-inverting input is connected to 0 V (ground). This means that the inverting input behaves as if it is at ground potential, despite not being connected to the actual ground.

Using the formula for an inverting amplifier: $V_{OUT} = V_{IN} \times \left( \frac{R_F}{R_{IN}} \right)$,

we have:

• Given that $V_{OUT} = 8 \ V$, $V_{IN} = 0.4 \ V$, and $R_{IN} = 1.8 \ k\Omega$,

we can rearrange for $R_F$: $R_F = \frac{V_{OUT}}{V_{IN}} \times R_{IN}$ Substituting in the values: $R_F = \frac{8 \ V}{0.4 \ V} \times 1.8 \ k\Omega = 36 \ k\Omega$.

The 555 IC is commonly used in controlling the positioning of servo devices in industrial applications.

The 555 IC operates in astable mode to generate square wave signals that can produce musical notes.

Transistor T1 acts as a switch in the 555 timer circuit, controlling the output based on the timing configuration.

The two comparators in the 555 IC function to compare the input voltage with predetermined threshold levels set by voltage dividers. Comparator 1 triggers the flip-flop when the input voltage exceeds 2/3 of the supply voltage, while comparator 2 resets it when the input drops below 1/3 of the supply voltage.

The flip-flop in the 555 timer circuit maintains the output state (high or low) based on the significant transitions from the comparators, thus controlling the timing and output drive of the circuit.