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T6B

ELECTRONIC AND ELECTRICAL COMPONENTS

Semiconductors: basic principles and applications of solid-state devices, diodes and transistors; Gain

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T6B011 of 12

Which is true about forward voltage drop in a diode?

Why A diode conducting in the forward direction always drops some voltage across its junction, and that value depends on the semiconductor material and construction. Silicon diodes drop roughly 0.7 volts, germanium about 0.3 volts, Schottky types around 0.2 to 0.3 volts, and LEDs anywhere from about 1.5 to 3 volts depending on color. That is why a designer picks a low-drop Schottky for an efficient power supply or rectifier.
Watch out Peak inverse voltage is a completely separate rating, the maximum reverse voltage the diode can block without breaking down, and it has no relationship to the small forward drop. The forward drop definitely does affect the load, since it subtracts from the voltage that reaches the load.
Silicon 0.7 V, germanium 0.3 V, Schottky 0.2 V: the drop depends on the type of diode.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B022 of 12

What electronic component allows current to flow in only one direction?

Why A diode is a semiconductor device with a PN junction that conducts when forward biased (anode positive relative to cathode) and blocks current when reverse biased, so current passes only one way. This is what makes diodes useful as rectifiers, converting AC into pulsating DC in power supplies, and as detectors in receivers.
Watch out A resistor limits current equally in both directions, and a fuse simply opens when current gets too high; neither cares about direction. A driven element is part of an antenna, not a circuit component that steers current.
Diode = one-way valve. The schematic arrow points the way current flows.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B033 of 12

Which of these components can be used as an electronic switch?

Why A transistor is a three-terminal active device in which a small current or voltage at the base (or gate) controls a much larger current between collector and emitter (or drain and source). Driving it hard on (saturation) makes it look like a closed switch, and driving it off (cutoff) makes it look like an open switch, with no moving parts. That same control action is what gives a transistor gain when it is biased in between those two extremes.
Watch out A potentiometer is a manually adjusted variable resistor, not an electronically controlled one, and a varistor or thermistor simply changes resistance in response to voltage or temperature rather than to a control signal.
Only the transistor has a control terminal: base in, switch or amplify out. The -istors just change resistance on their own.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B044 of 12

Which of the following components can consist of three regions of semiconductor material?

Why A bipolar junction transistor is made from three doped semiconductor regions arranged as NPN or PNP: the emitter, the base, and the collector. Current flowing into the thin base region controls a much larger current between emitter and collector, which is how the device provides gain. A diode, by contrast, has only two regions and one junction.
Watch out A triode is a vacuum tube with three electrodes (cathode, grid, plate), not semiconductor regions, and a pentode is a five-element tube; an alternator is a rotating machine that generates AC.
Tri-ode and penta-ode are tubes counting electrodes; the transistor counts three doped regions: emitter, base, collector.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B055 of 12

What type of transistor has a gate, drain, and source?

Why A field-effect transistor (FET) has three terminals named gate, source, and drain. The voltage on the gate creates an electric field that widens or narrows the conducting channel between source and drain, controlling current with essentially no gate current. That is different from a bipolar transistor, which is controlled by base current.
Watch out The bipolar junction transistor is the tempting choice, but its three terminals are the base, emitter, and collector. A varistor is a voltage-dependent resistor, not a transistor, and a Hall-effect device is a magnetic field sensor.
FET = Gate, Drain, Source. BJT = Base, Emitter, Collector. Gate means field-effect.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B066 of 12

How is the cathode lead of a semiconductor diode often marked on the package?

Why Diodes conduct current in one direction only, so the package must show which end is the cathode (the negative end, where the arrow of the schematic symbol points and where current exits in forward conduction). Manufacturers mark that end with a band or stripe printed around the body. The unmarked end is the anode.
Watch out Letters like C or K are used for the cathode in schematics and datasheets, but they are not printed on small diode bodies, and there is no room to spell out a word on a typical glass or plastic package.
Stripe = cathode, and the schematic symbol's bar is the same stripe. Band matches the bar.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B077 of 12

What causes a light-emitting diode (LED) to emit light?

Why An LED is a diode, so it only conducts when forward biased, meaning the anode is positive with respect to the cathode. As that forward current flows across the junction, electrons recombine with holes and release the energy as photons. No current, no light, so the LED's brightness tracks the forward current through it (which is why a series resistor is used to limit it).
Watch out Reverse current is what a diode blocks; applying reverse voltage gives only tiny leakage and, if you exceed the reverse breakdown rating, you damage the LED rather than light it.
LEDs are forward-thinking: current has to flow forward through the junction to make light.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B088 of 12

What does the abbreviation FET stand for?

Why FET stands for Field Effect Transistor. Unlike a bipolar transistor, which is controlled by current into its base, an FET is controlled by the voltage (electric field) applied to its gate, which widens or pinches off the conducting channel between source and drain. That voltage control means an FET gate draws almost no current, giving it very high input impedance.
Watch out The choices containing 'Transmitter' are a giveaway that they are wrong: an FET is a device inside a circuit, not a transmitter. 'Fast Electron Transistor' is not a real term.
F-E-T: Field Effect Transistor. Voltage at the gate makes the field; current flows source to drain.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B099 of 12

What are the names for the electrodes of a diode?

Why A diode has just two electrodes: the anode (the P-type side) and the cathode (the N-type side). Conventional current flows into the anode and out the cathode when the diode is forward biased; it blocks current in the reverse direction. On most diode packages the cathode is marked with a band.
Watch out Source and drain are two of the three terminals of a field effect transistor, and gate and base belong to FETs and bipolar transistors respectively, so those all describe three-terminal devices, not a diode.
Two letters, two terminals: A for Anode (current in), C for Cathode (banded end, current out).
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B1010 of 12

Which of the following can provide power gain?

Why Power gain means the output signal carries more power than the input signal, and that extra power has to come from a DC supply. A transistor is an active device: a small base current (or gate voltage) controls a much larger current drawn from the power supply, so the signal power out can far exceed the signal power in. Passive parts have no supply to draw from, so they can never produce power gain.
Watch out A transformer is the tempting one because it can step voltage up, but voltage gain is not power gain: the current drops in the same proportion, and real transformers deliver slightly less power than they take in. Resistors only dissipate power, and a reactor (inductor) stores and returns energy without adding any.
Gain needs a power supply. Only the transistor has one plugged in; transformers just trade volts for amps.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B1111 of 12

What does the term gain mean in amplifiers?

Why Gain is simply the ratio of what comes out of a stage to what goes in, and that ratio can be measured in any of three quantities. Voltage gain compares output voltage to input voltage, current gain compares output current to input current, and power gain compares output power to input power. A transistor amplifier can have gain in all three senses at once, and which one you quote depends on what the circuit is being used for. Gains are often expressed in decibels, where 10 dB of power gain means the output power is 10 times the input power.
Watch out Picking only the voltage ratio is tempting because that is the figure most often quoted for audio and RF stages, but it is just one of the three valid ways to express gain.
Gain = out divided by in, and the pool lets you measure it in volts, amps or watts.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
T6B1212 of 12

What are the names of the electrodes of a bipolar junction transistor?

Why A bipolar junction transistor is built from three doped semiconductor regions: the emitter, the thin base in the middle, and the collector. A small current into the base controls a much larger current flowing between emitter and collector, which is how the device provides current gain. Field effect transistors use different names for their three electrodes: gate, source and drain.
Watch out Terms like input, output and supply describe roles in a circuit, not the physical electrodes of the device; any transistor terminal can serve as an input or output depending on the amplifier configuration.
BJT = Base, Emitter, Collector. FET = Gate, Source, Drain. Base and gate are the control terminals.
HamSandwich explanation, first draft. The question and answers are the NCVEC text.
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