Transistors

31 questions

All types31 Multiple choice17 True / False8 Matching6

In a bipolar junction transistor circuit, a small input current supplied to the base terminal is used to control a significantly larger current flowing between which two terminals?

The gate and the source

The collector and the emitter

The anode and the cathode

The base and the power supply rail

Show answer & explanation

Answer: The collector and the emitter

Answer

The collector and the emitter

A bipolar junction transistor functions as a current-controlled amplifier or switch. A relatively small base current (

I_B

) modulates a significantly larger current (

I_C

) flowing across the main conduction channel between the collector and the emitter.

Step-by-Step Solution

Identify the component type and its standard terminal leads.

A bipolar junction transistor (BJT) consists of three active terminals: the base (B), collector (C), and emitter (E).

Terminal designations distinguish BJTs from other semiconductor devices such as FETs or diodes.

Determine the functional relationship between the input control lead and the main output conduction channel.

A small current entering the base terminal forward-biases the base-emitter junction, permitting a much larger current (proportional by the gain factor beta) to flow between the collector and the emitter.

BJTs operate as current-controlled devices where the base-emitter circuit governs the primary collector-to-emitter current channel.

Key Concept

Bipolar Junction Transistor (BJT) terminal roles and current amplification principle

Estimated Time:45s

Question 22Question →

Match each fundamental transistor operating concept on the left with its correct electrical definition on the right.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Amplification matches 'Using a small varying input signal to control a larger output signal'; Switching matches 'Alternating between full conduction and complete cutoff to control power to a load'; Biasing matches 'Applying preset DC voltages to establish a stable quiescent operating point'.

Each concept pairs directly with its fundamental role in electronics: Amplification scales a small input variation into a larger output signal; Switching toggles between full conduction and total cutoff to activate or deactivate loads; Biasing establishes the necessary static direct-current voltages across terminals for stable circuit operation.

Step-by-Step Solution

Identify the definition of signal amplification in solid-state electronics.

Amplification corresponds to increasing signal strength by using small input fluctuations to modulate larger power supplies.

In linear active mode, transistors amplify weak audio, radio, or sensor signals.

Identify the functional definition of electronic switching.

Switching corresponds to toggling between saturation (closed/on) and cutoff (open/off).

Digital and power control circuits use transistors as high-speed electronic switches without moving parts.

Identify the purpose and definition of transistor biasing.

Biasing corresponds to setting baseline DC voltage levels at the terminals.

Proper DC bias ensures the semiconductor junctions maintain the required operational state (forward-biased base-emitter, reverse-biased base-collector).

Key Concept

Core operational principles and functional modes of transistors

Estimated Time:45s

Question 23Question →

An electronics technician is analyzing solid-state circuit topologies for an audio and radio frequency transceiver. Match each transistor circuit configuration or operational mode with its defining electrical characteristic.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Common Emitter Configuration matches with significant voltage/current gain and

180^\circ

phase inversion; Common Collector Configuration matches with high input impedance, low output impedance, and near-unity voltage gain; Common Base Configuration matches with low input impedance, high voltage gain, and no phase inversion for high-frequency RF; Transistor Switch Mode matches with alternating between cutoff and saturation to control load power.

Each transistor configuration serves a specific role determined by which terminal is common to both input and output: Common Emitter is the primary inverting voltage/current amplifier; Common Collector serves as a non-inverting impedance buffer with unity voltage gain; Common Base provides low input impedance and high-frequency stability without phase shift; and Switch Mode drives the transistor between saturation and cutoff for binary power control.

Step-by-Step Solution

Identify the phase relationship and gain characteristics of the Common Emitter amplifier.

The Common Emitter takes input at the base and extracts output at the collector, yielding voltage gain, current gain, and a

180^\circ

phase inversion.

This is the signature standard amplifier configuration in bipolar transistor circuitry.

Analyze the impedance transformation and voltage gain of the Common Collector configuration.

The Common Collector takes input at the base and extracts output at the emitter, yielding a voltage gain of slightly less than 1 with high input impedance and low output impedance.

This configuration acts as a buffer or impedance matching stage, commonly termed an emitter follower.

Identify the high-frequency and impedance properties of the Common Base configuration.

The Common Base takes input at the emitter and output at the collector with the base grounded for AC signals, offering low input impedance and no signal inversion.

The grounded base shields input from output, mitigating the Miller effect in RF circuits.

Distinguish linear amplification from digital switching operation.

Switching mode avoids the active linear region and toggles strictly between cutoff (

I_C = 0

) and saturation (

V_{CE} \approx 0.2\text{ V}

Digital control and relay driving rely on binary on/off states rather than linear proportional amplification.

Key Concept

Transistor Circuit Configurations and Operating Modes

Estimated Time:1m 0s

Question 24Question →

In a field-effect transistor (FET), which terminal serves as the control element that regulates the current passing between the source and the drain?

Base

Gate

Collector

Cathode

Show answer & explanation

Answer: Gate

Answer

Gate

In a field-effect transistor (FET), the gate terminal applies an electric field that alters the conductivity of the semiconductor channel, thereby regulating the flow of current between the source and the drain.

Step-by-Step Solution

Identify the transistor family specified in the question.

The device is a field-effect transistor (FET), which utilizes Gate, Source, and Drain terminals.

Field-effect transistors use different terminal designations and operational principles compared to bipolar junction transistors.

Determine the functional role of each FET terminal.

Current enters at the source and leaves through the drain, while voltage applied to the gate controls channel conductivity.

The gate terminal acts as the primary control electrode that modulates current flow between the source and drain.

Key Concept

Field-Effect Transistor (FET) Terminal Designations and Roles

Estimated Time:45s

Question 25Question →

While standard bipolar junction transistors (BJTs) operate as current-controlled components, field-effect transistors (FETs) are commonly used in high-impedance input stages. What is the primary operating mechanism of a field-effect transistor?

Controlling collector current by drawing a continuous input current through a forward-biased base junction

Regulating current between the source and drain using an electric field established by a gate voltage

Directing electron flow by altering magnetic flux across a series of reverse-biased diode barriers

Modulating channel resistance by requiring a high input control current at the gate terminal

Show answer & explanation

Answer: Regulating current between the source and drain using an electric field established by a gate voltage

Answer

Regulating current between the source and drain using an electric field established by a gate voltage

A field-effect transistor (FET) controls the flow of electrical charge carriers between the source and drain terminals by varying the strength of an electrostatic field within the semiconductor channel. This field is established by applying a voltage to the gate terminal, allowing the device to modulate conductivity with almost zero input gate current.

Step-by-Step Solution

Identify the fundamental category and terminals of a Field-Effect Transistor (FET)

FETs have three primary terminals: Gate, Drain, and Source.

Recognizing terminal designations separates FET functionality from BJT terminals (Base, Collector, Emitter).

Determine the control mechanism of a FET

An electric field created by voltage applied to the gate controls the conductive channel between the source and drain.

FETs are voltage-controlled solid-state devices that draw negligible gate current due to extremely high input resistance.

Key Concept

Field-Effect Transistor (FET) Voltage-Controlled Operation

Estimated Time:1m 0s

Question 26Question →

For a bipolar junction transistor (BJT) to operate in the active amplification mode, the base-emitter junction must be forward-biased while the base-collector junction is reverse-biased.

True

False

Show answer & explanation

Answer: True

Answer

True. Operating a bipolar junction transistor in the active amplification region requires a forward-biased base-emitter junction and a reverse-biased base-collector junction.

The statement is correct because linear amplification in a bipolar junction transistor strictly requires the input base-emitter diode junction to be forward-biased to initiate current flow, and the output collector-base junction to be reverse-biased to sweep and gather charge carriers into the collector circuit.

Step-by-Step Solution

Identify the specified operating state of the transistor

The transistor is designated to operate in active (linear) amplification mode.

A transistor exhibits distinct junction biasing configurations depending on whether it functions in cutoff, saturation, or active mode.

Determine the required bias across the base-emitter junction

The base-emitter junction must be forward-biased.

Forward-biasing this junction overcomes the internal barrier potential (approximately 0.7 V for silicon) and injects carriers into the base.

Determine the required bias across the base-collector junction

The base-collector junction must be reverse-biased.

Reverse-biasing this junction establishes a wide depletion region with an electric field that sweeps the injected carriers into the collector.

Evaluate the accuracy of the statement

The statement correctly describes both required junction conditions.

The combination of a forward-biased base-emitter junction and a reverse-biased base-collector junction precisely defines active region operation.

Key Concept

Bipolar Junction Transistor Biasing and Operating Modes

Estimated Time:45s

Question 27Question →

In a bipolar junction transistor (BJT) amplifier circuit operating in its active region, a base current ( $I_B$ ) of $2\text{ mA}$ is applied. If the transistor has a common-emitter DC current gain ( $\beta$ or $h_{FE}$ ) of $50$ , what is the resulting collector current ( $I_C$ ) flowing through the transistor?

25\text{ mA}

52\text{ mA}

100\text{ mA}

0.04\text{ mA}

Show answer & explanation

Answer: $100\text{ mA}$

Answer

The collector current (

I_C

) is

100\text{ mA}

In the active region of a bipolar junction transistor, the collector current is directly proportional to the base current by the factor of DC current gain:

I_C = \beta \times I_B

. Multiplying the base current of

2\text{ mA}

by the gain of

50

yields

100\text{ mA}

Step-by-Step Solution

Identify the given values and formula for transistor DC current gain in the active region.

Given

I_B = 2\text{ mA}

and

\beta = 50

. The governing formula is

I_C = \beta \times I_B

Current gain (

\beta

) represents the amplification factor between the controlling base current and the controlled collector current.

Substitute the measured base current and gain into the current equation.

I_C = 50 \times 2\text{ mA} = 100\text{ mA}

Calculating the product gives the total current flowing through the collector terminal.

Key Concept

Bipolar Junction Transistor DC Current Gain (

\beta

h_{FE}

)

Estimated Time:1m 0s

Question 28Question →

Electronic systems utilize various solid-state semiconductor transistors tailored for specific switching, amplification, and sensing applications. Match each transistor type to its defining operating principle and physical characteristic.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Bipolar Junction Transistor (BJT) pairs with the current-controlled device using both electron and hole carriers; Junction Field-Effect Transistor (JFET) pairs with the voltage-controlled device using a reverse-biased PN junction; Metal-Oxide-Semiconductor FET (MOSFET) pairs with the insulated-gate component featuring high input impedance and an oxide dielectric; Phototransistor pairs with the optoelectronic component converting incident light into amplified collector current.

Each semiconductor device corresponds uniquely to its operating physics: BJTs are bipolar current-controlled devices; JFETs utilize reverse-biased PN junctions for channel modulation; MOSFETs employ an insulated dielectric gate for field-effect control; and phototransistors utilize optical stimulation to generate base-region carriers.

Step-by-Step Solution

Identify the carrier conduction and control mechanism of the BJT

The BJT is a current-controlled bipolar device relying on both majority and minority carriers (electrons and holes).

The term bipolar explicitly indicates the participation of both carrier polarities, controlled by base current.

Differentiate between the field-effect transistor junction types (JFET vs. MOSFET)

The JFET relies on a direct reverse-biased PN gate junction, while the MOSFET incorporates an insulated oxide layer that eliminates DC gate current entirely.

The metal-oxide insulator in a MOSFET provides near-infinite input impedance compared to the reverse-biased PN junction of a JFET.

Distinguish the optoelectronic sensor category (Phototransistor)

The phototransistor operates by replacing or augmenting electrical base current with photon-generated charge carriers.

Light striking the transparent casing generates electron-hole pairs at the junction to initiate conduction.

Key Concept

Classification, control mechanisms, and structural properties of major transistor families

Estimated Time:1m 0s

Question 29Question →

An electronics technician is testing a bipolar junction transistor (BJT) configured as an electronic switch. When the base receives sufficient input voltage and current to drive the transistor into full conduction with minimum resistance between the collector and emitter, in which operating region is the transistor functioning?

Cutoff region

Saturation region

Active region

Breakdown region

Show answer & explanation

Answer: Saturation region

Answer

Saturation region

When a bipolar junction transistor is driven with sufficient base current to achieve maximum conduction, it operates in the saturation region. In saturation, both internal PN junctions are forward-biased, reducing the collector-to-emitter voltage (

V_{CE}

) to a fraction of a volt (typically around

0.2\text{ V}

), effectively behaving like a closed mechanical switch.

Step-by-Step Solution

Identify the circuit role and desired state of the transistor

The transistor operates as an electronic switch driven into full conduction (fully ON).

Transistors in switching circuits toggle between two primary binary states: fully OFF and fully ON.

Relate the fully ON switching condition to the characteristic BJT operating regions

Full conduction with minimal collector-to-emitter voltage drop occurs in the saturation region.

When both the base-emitter and base-collector junctions become forward-biased due to sufficient base drive, the transistor enters saturation, maximizing current flow through the load.

Key Concept

BJT Operating Regions and Switching States

Estimated Time:1m 0s

Question 30Question →

In standard electronic schematic symbols for bipolar junction transistors (BJTs), the arrow is located on the emitter terminal and points outward away from the base for an NPN transistor, indicating the direction of conventional current flow.

True

False

Show answer & explanation

Answer: True

Answer

True

The statement is true because electronic schematic standards place the directional arrow exclusively on the emitter lead. For an NPN transistor, this arrow points outward (away from the base), which reflects the direction of conventional current flow across the forward-biased base-emitter junction.

Step-by-Step Solution

Identify the specific terminal that carries the directional arrow on a BJT schematic symbol.

The arrow is always placed on the emitter terminal, distinguishing it from the collector and base leads.

Standard electronic schematic conventions designate the emitter lead with an arrow to define transistor polarity and terminal identity.

Determine the orientation of the arrow for an NPN transistor configuration.

In an NPN transistor, the arrow points outward, away from the base.

The arrow represents the direction of forward-biased conventional current flow, moving from the P-type base material out through the N-type emitter material.

Evaluate the accuracy of the full statement.

The statement correctly identifies both the terminal location (emitter) and the outward direction for an NPN transistor.

Both structural elements conform exactly to standard electrical schematic rules.

Key Concept

BJT schematic symbol identification and terminal arrow direction

Estimated Time:45s

Question 31Question →

A technician is configuring a PNP bipolar junction transistor to operate as a switch. To forward-bias the base-emitter junction and turn the transistor ON, what electrical condition must be established at the base terminal relative to the emitter?

The base voltage must be higher (more positive) than the emitter voltage.

The base voltage must be lower (more negative) than the emitter voltage.

The base must receive conventional current flowing into it from the main positive supply rail.

The base voltage must be held at the exact same potential as the collector terminal.

Show answer & explanation

Answer: The base voltage must be lower (more negative) than the emitter voltage.

Answer

The base voltage must be lower (more negative) than the emitter voltage.

For a PNP bipolar junction transistor to turn ON, its base-emitter P-N junction must be forward-biased. Because the emitter is P-type semiconductor material and the base is N-type material, the base terminal must be held at a lower (more negative) electrical potential than the emitter terminal (typically by at least

0.7\text{ V}

in standard silicon transistors).

Step-by-Step Solution

Identify the transistor polarity and internal semiconductor structure.

A PNP transistor consists of an N-type base sandwiched between a P-type emitter and a P-type collector.

Understanding layer material types determines the required voltage polarities across the junctions.

Determine the biasing requirement for the base-emitter junction to allow conduction.

To forward-bias a P-N junction (P-type emitter to N-type base), the P-type region must be more positive than the N-type region.

Current can only flow across a forward-biased junction when the appropriate potential difference overcomes the barrier voltage (typically

0.7\text{ V}

for silicon).

Formulate the necessary base terminal condition relative to the emitter.

The base voltage must be pulled lower (more negative) relative to the emitter voltage, allowing conventional current to flow out of the base.

This establishes forward bias at the base-emitter junction, switching the PNP transistor ON.

Key Concept

PNP Transistor Biasing and Conduction Principles

Estimated Time:1m 0s

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