Refer to FIGURE 4.1 below and answer the questions that follow - NSC Electrical Technology Electronics - Question 4 - 2021 - Paper 1

The polarity of the pulse provided on the inverting input when switch S1 is pressed is positive.

The 741 op-amp acts as a comparator that compares the two voltages on its input. It also functions as an amplifier for the input signals that drives the output to one of its saturation states.

The LED indicated as LED1 (red) will be forward biased when S1 is pressed.

The polarity of the voltage present on pin 3 after switch S1 is pressed is positive.

The value of the voltage across capacitor C2 when the circuit is in its natural resting position is -9V.

When the circuit output changes state, the voltage at point B is +9V.

The circuit output will change state when a trigger pulse greater than -V_in is applied to the inverting input.

The resistor R1 and the capacitor C2 are responsible for charging capacitor C2.

The output will keep oscillating between high and low states because both the trigger pin 2 and threshold pin 6 are connected to the top of the timing capacitor.

The 741 IC op-amp equivalent should include labels for the non-inverting and inverting inputs, the output, and the power supply connections.

A summing amplifier is used to add two or more different input signals to create one amplified output signal.

The output voltage at C can be calculated using the formula: V_{out} = -rac{V_{1}}{R_1}R_f + -rac{V_{2}}{R_2}R_f + -rac{V_{3}}{R_3}R_f

The feedback at A can be calculated using the relation: $R_f = (V_{out} / (V_{1} + V_{2} + V_{3})) * R_{total}$, where $R_{total}$ is derived from the combination of R1, R2, and R3.

Substituting appropriate values will yield: V_{out} = -rac{(0.5)(R_f)}{20000} -rac{(1.2)(R_f)}{40000} -rac{(0.9)(R_f)}{20000}

FIGURE 4.6(a) is a passive RC differentiator, while FIGURE 4.6(B) is a passive RC integrator.

With a long time constant, the left hand plate of the capacitor immediately charges up to positive potential, then discharges slowly, causing a gradual change when the input swings to the opposite potential.

The function of the circuit in FIGURE 4.6(B) is to change square waves into triangular waves.

The output waveform will exhibit a corresponding linear change reflecting the input sine wave, maintaining the orientation of peaks and troughs.

The output waveform will exhibit a triangular shape that reflects the transitions of the square wave input.

The op amp improves the circuit by providing high input impedance and low output impedance, enabling better signal integrity and larger gain.