Mixed Deck — All ISCET Topics Flashcards

A network analyzer measures the S11 (return loss) of an antenna and displays −20 dB. This means the antenna is reflecting what percentage of the incident power?

Answer: 1%

−20 dB return loss means reflected power = 10^(−20/10) = 0.01 = 1% of incident power.

When measuring a transistor's beta (hFE) with a DMM in transistor test mode, the reading is 0. This indicates:

Answer: The transistor's base-emitter junction is open or the device is faulty

A beta reading of 0 indicates the transistor cannot amplify current, pointing to an open base-emitter junction or a completely failed device.

A series AC circuit consists of a 30 Ω resistor and a capacitor with a capacitive reactance (XC) of 40 Ω. What is the total impedance (Z) of this circuit?

Answer: 50 Ω

For a series RC circuit, the total impedance (Z) is calculated using the formula Z = √(R² + XC²). In this case, R = 30 Ω and XC = 40 Ω. So, Z = √(30² + 40²) = √(900 + 1600) = √2500 = 50 Ω. Impedance represents the total opposition to current flow in an AC circuit.

In AC circuit analysis, Kirchhoff's Voltage Law (KVL) applies to:

Answer: Phasor (complex) voltages around a loop

KVL applies to AC circuits using phasor (complex number) representation, so phasor voltages around any closed loop sum to zero.

In a wiring diagram, what is the difference between a 'wiring diagram' and a 'schematic diagram'?

Answer: Wiring diagrams show physical locations and connections; schematics show functional/electrical relationships using standardized symbols

A wiring diagram shows the physical layout and actual connections between components, while a schematic uses standardized symbols to show electrical relationships regardless of physical location.

What measurement does an LCR meter make that a standard DMM cannot?

Answer: Inductance and capacitance values

An LCR meter measures inductance (L), capacitance (C), and resistance (R) at specific test frequencies, which is beyond the capability of a standard DMM.

A zener diode in a voltage regulator circuit measures 0 V across it under load. What fault is indicated?

Answer: Zener is shorted

A shorted zener diode will drop 0 V, collapsing the regulated output voltage to near zero.

In a voltage divider circuit with R1 = 10 kΩ (top) and R2 = 5 kΩ (bottom) connected to 15 V, what is the output voltage across R2?

Answer: 5 V

Vout = Vin × R2/(R1+R2) = 15 × 5k/(10k+5k) = 15 × 1/3 = 5 V.

Which type of counter produces a modulus that is not a power of two by using feedback to skip states?

Answer: Modulo-N counter

A modulo-N counter uses decode-and-reset or feedback logic to count to N−1 then recycle, regardless of whether N is a power of two.

A technician is designing a circuit that needs to select one of eight data inputs and route it to a single output. Which digital logic device is most suitable for this task?

Answer: Multiplexer (MUX)

A Multiplexer (MUX), also known as a data selector, is a combinational logic circuit designed to switch one of several input lines through to a single common output line. An 8-to-1 multiplexer would use three select lines (2^3 = 8) to choose which of the eight inputs is passed to the output.

A half-wave rectifier is connected to a 120V RMS transformer secondary. What is the approximate average DC output voltage (ignoring diode drop)?

Answer: 54V

For a half-wave rectifier, Vavg = 0.318 × Vpeak = 0.318 × (120 × 1.414) ≈ 0.318 × 169.7 ≈ 54V.

What is the primary advantage of using a True RMS multimeter compared to a more basic averaging (mean-responding) multimeter?

Answer: It provides more accurate measurements of non-sinusoidal AC waveforms.

Averaging multimeters are only accurate for pure sine waves. A True RMS meter accurately calculates the effective (heating) value of any AC waveform, including square waves, pulse-width modulated signals, and other distorted waveforms common in modern electronics like variable speed drives and computers.

What is the significance of the depletion approximation used in p-n junction analysis?

Answer: It assumes the depletion region has zero free carriers and the neutral regions have no charge

The depletion approximation assumes the depletion region is fully depleted of free carriers (abrupt edges) and neutral regions are charge-free, simplifying junction width calculations.

A varactor (varicap) diode is used primarily as a:

Answer: Voltage-controlled capacitor

A varactor diode exploits the voltage-dependent capacitance of its reverse-biased depletion region, making it useful as a voltage-controlled capacitor in tuning circuits.

What is the purpose of a technical datasheet?

Answer: To provide component specifications

A technical datasheet is a document that provides detailed technical specifications and characteristics of an electronic component. It includes crucial information such as electrical ratings, pin configurations, operating conditions, and performance curves. Engineers and technicians rely on datasheets to select appropriate components and design reliable circuits.

Which statement correctly describes a depletion-mode MOSFET?

Answer: It conducts at zero gate-to-source voltage

A depletion-mode MOSFET has a physical channel and is normally on (conducting) when VGS = 0.

In a J-K flip-flop, what is the output behavior when both J and K inputs are held HIGH (logic 1) and a clock pulse is applied?

Answer: The output toggles to the opposite state.

When both J and K inputs of a J-K flip-flop are held HIGH, the flip-flop is in the 'toggle' mode. On each active clock edge, the output Q will invert to the opposite of its current state.

A technician needs to control a high-power AC load, such as a motor, using a low-power DC signal. Which three-terminal semiconductor device is most suitable for this application, acting as a latching switch?

Answer: Silicon-Controlled Rectifier (SCR)

A Silicon-Controlled Rectifier (SCR) is a type of thyristor designed to control large currents and voltages with a small gate current. Once triggered by a pulse to its gate, it 'latches' on and conducts current from anode to cathode until the current falls below a holding threshold, making it perfect for controlling AC power.

Probing a CMOS logic circuit with a standard 1× passive probe can alter circuit behavior because the probe's capacitance:

Answer: Loads the node and can reduce the signal's rise time or cause oscillations to stop

Probe input capacitance (10–100 pF for 1× probes) adds a load that slows signal edges and can de-stabilize high-frequency circuits.

What is propagation delay in a logic gate?

Answer: Time for the output to settle after an input change

Propagation delay (tpd) is the time interval between a change at the input and the resulting change at the output of a gate.