4.1 Name the semiconductor that is represented by the symbol in FIGURE 4.1 - NSC Electrical Technology Electronics - Question 4 - 2024 - Paper 1

Section A is the Silicon dioxide insulation, and Section B is the Enhanced channel.

The MOSFET mode represented in FIGURE 4.3 is the Enhancement mode, where the application of a positive voltage creates a conductive channel between the source and drain.

The main difference is that a JFET operates in the depletion mode, using a reverse-biased gate to control current, whereas a MOSFET can operate in either enhancement mode or depletion mode, providing greater flexibility.

R1 protects the UJT by limiting the discharge current to a safe value, preventing damage to the device.

When a negative pulse is applied to the emitter, the pn junction is reverse biased, which means the emitter current is cut off and the UJT is in the OFF state.

The output waveform across B2 of the UJT will be a saw-tooth waveform, indicating the charging and discharging cycles as the UJT operates.

For the given conditions when V2 and V1 are in phase, the output state of the op amp will be positive, indicating that Vout is high.

Op amps are not frequently used in open-loop mode because their high gain can lead to instability, making the output voltage highly sensitive to small input variations.

The bandwidth refers to the range of frequencies over which an operational amplifier can operate effectively without significant gain loss.

Using the formula $V_{out} = V_{in} \times \left( \frac{R_{F}}{R_{in}} + 1 \right)$ with $V_{in} = 60 mV, R_{F} = 10 k\Omega, R_{in} = 1 k\Omega$, we find: $V_{out} = 60 \times 10^{-3} \times \left( \frac{10 \times 10^{3}}{1 \times 10^{3}} + 1 \right) = 0.6 V = 600 mV$.

Using the formula $R_{F} = R_{in} \times \left( \frac{V_{out}}{V_{in}} - 1 \right)$ and substituting $V_{in} = 0.5 V, V_{out} = 4 V, R_{in} = 2 k\Omega$, we get $R_{F} = 2 \times 10^{3} \times \left( \frac{4}{0.5} - 1 \right) = 15.99 k\Omega \approx 16 k\Omega$.

Pin 7 is the discharge pin.

One application of a 555 IC in monostable mode is as a pulsewidth modulator.

Pin 4 is the reset pin for the flip-flop; it resets the output to zero volts when activated.