Electronics Design Engineering Flashcards

Question 1

What does Ohm's law state about voltage, current, and resistance?

Accepted Answer

Ohm's law states that the voltage across a resistor equals the current through it multiplied by its resistance, written as V equals I times R. The relationship holds for ideal linear resistors at constant temperature. Engineers use it to predict current when a known voltage is applied.

Question 2

What is Kirchhoff's current law, and where is it applied?

Accepted Answer

Kirchhoff's current law states that the total current entering a node equals the total current leaving it, so charge is never created or destroyed at a junction. It applies at any point where branches meet. Writing one equation per node lets you solve currents in complex networks.

Question 3

How do resistances combine when resistors are wired in series and in parallel?

Accepted Answer

In series, resistances add, so the total equals the sum of each value, and the same current flows through every element. In parallel, the reciprocal of the total equals the sum of the reciprocals, so the combined value is always smaller than the smallest branch. Each parallel branch sees the same voltage across it.

Question 4

What is the difference between voltage and current in a circuit?

Accepted Answer

Voltage is the electrical potential difference between two points, measured in volts, and it drives charge to move. Current is the rate of charge flow through a conductor, measured in amperes. A battery sets up voltage, while the load connected to it determines how much current actually flows.

Question 5

How is electrical power calculated, and which units are used?

Accepted Answer

Electrical power equals voltage multiplied by current, P equals V times I, and it is measured in watts. Using Ohm's law, power can be written as current squared times resistance or voltage squared divided by resistance. Ratings matter because a resistor or regulator that dissipates more than its rating will overheat and may fail.

Question 6

What is a voltage divider and when is it useful?

Accepted Answer

A voltage divider is two series resistors across a source, producing an output voltage at their junction that is a fraction of the input. The output equals the input multiplied by R2 divided by the sum of R1 and R2. It is useful for setting reference levels and scaling signals for measurement.

Question 7

Why is it important to consider power dissipation when selecting resistors?

Accepted Answer

A resistor converts electrical energy into heat, and its wattage rating states the maximum heat it can handle safely. If the actual dissipation exceeds that rating, the resistor can overheat, change value, or burn out. Designers usually choose a rating well above the calculated power to allow for ambient temperature and tolerance.

Question 8

What is the purpose of a fuse or current limit in a circuit?

Accepted Answer

A fuse or current limit protects a circuit by interrupting or restricting current when it exceeds a safe level, which prevents wire heating, component damage, and fire. A fuse contains a metal element that melts when overloaded, while a current limit reduces output current electronically. Ratings are chosen from normal operating current and wiring capacity.

Question 9

What does a resistor do in a circuit, and what is its unit?

Accepted Answer

A resistor opposes the flow of current, limiting current and dividing voltage according to its value. Its unit is the ohm, symbolized by the Greek letter omega. Resistors are used for biasing transistors, setting gain in amplifiers, pulling signal lines to a known level, and protecting sensitive inputs from excess current.

Question 10

What is a capacitor and how does it store energy?

Accepted Answer

A capacitor consists of two conductors separated by an insulator, called a dielectric, and it stores energy in an electric field. The stored charge equals capacitance multiplied by voltage, measured in farads. Because a capacitor resists sudden voltage changes, it is useful for smoothing supplies, filtering signals, and holding a voltage briefly during timing.

Question 11

What is an inductor, and how does it respond to changing current?

Accepted Answer

An inductor is a coil of wire that stores energy in a magnetic field when current flows through it. It opposes changes in current by producing a voltage proportional to the rate of change of current. Its unit is the henry, and it is common in filters, switching power supplies, and radio circuits.

Question 12

What is the time constant of an RC circuit and what does it describe?

Accepted Answer

The time constant of an RC circuit equals resistance multiplied by capacitance, written tau equals R times C, with units of seconds. It describes how quickly a capacitor charges or discharges. After one time constant, the voltage has reached about 63 percent of its final change, and after five time constants it is essentially settled.

Question 13

Why are real capacitors and resistors not perfectly ideal in circuits?

Accepted Answer

Real components include parasitic effects that ideal models ignore, such as series inductance in capacitors and lead inductance in resistors. Resistors also have tolerance, a range around their nominal value, and their values can drift with temperature. Capacitors may have leakage current and equivalent series resistance, which affect ripple, filtering, and high frequency performance.

Question 14

How do you choose between an electrolytic and a ceramic capacitor?

Accepted Answer

Electrolytic capacitors offer large capacitance in a small package, but they are polarized, have higher equivalent series resistance, and age over time. Ceramic capacitors are non-polarized, stable, and well suited to high frequency decoupling, though their capacitance can drop with voltage and temperature. Designers often combine both for bulk storage and fast local response.

Question 15

What is a transformer, and how does it change voltage?

Accepted Answer

A transformer uses two coils linked by a shared magnetic core so that alternating current in the primary coil induces voltage in the secondary coil. The voltage ratio equals the turns ratio for an ideal transformer, so a transformer can step voltage up or down. It works only with changing current, and it provides electrical isolation between circuits.

Question 16

What does a potentiometer do, and how is it used as a voltage control?

Accepted Answer

A potentiometer is a three-terminal variable resistor whose wiper position sets how much of the resistive track lies between terminals. Used as a voltage divider, it lets a user adjust an output voltage, such as volume or brightness control. Its power rating must suit the circuit, since small potentiometers handle little power.

Question 17

What is a semiconductor, and why is silicon widely used?

Accepted Answer

A semiconductor is a material whose electrical conductivity lies between that of a conductor and an insulator, and it can be controlled by doping and applied fields. Silicon is widely used because it forms a stable oxide layer, is abundant, and supports reliable manufacturing of transistors and integrated circuits.

Question 18

How does doping change the behavior of silicon?

Accepted Answer

Doping adds small amounts of impurity atoms to silicon to create extra charge carriers. Donor atoms such as phosphorus add free electrons, producing n type material, while acceptor atoms such as boron create holes, producing p type material. Joining the two types forms a junction that underlies diodes and transistors.

Question 19

What is a diode, and what is its basic behavior?

Accepted Answer

A diode is a two-terminal device that conducts current mainly in one direction, with low resistance when forward biased and very high resistance when reverse biased. A silicon diode typically drops about 0.7 volts when conducting. Diodes are used for rectification, protection against reversed supply polarity, and signal clipping.

Question 20

What is a Zener diode used for in a circuit?

Accepted Answer

A Zener diode is designed to conduct in reverse once the voltage across it reaches a specified Zener voltage, holding that voltage nearly constant. This makes it useful as a simple voltage reference or shunt regulator. It must be paired with a series resistor so its reverse current stays within its power rating.

Question 21

How does a bipolar junction transistor amplify a signal?

Accepted Answer

A bipolar junction transistor uses a small base current to control a much larger collector current, so a small input change produces a larger output change. For an NPN device in active mode, collector current is approximately beta times base current. Amplification depends on biasing the transistor correctly to keep it in the active region.

Question 22

What is a MOSFET, and how is it controlled?

Accepted Answer

A MOSFET is a metal oxide semiconductor field effect transistor whose current between drain and source is controlled by the voltage on its gate. Because the gate is insulated, it draws almost no steady current, unlike a bipolar transistor. MOSFETs are common in switching power circuits, digital logic, and amplifiers.

Question 23

What does a transistor do when used as a switch?

Accepted Answer

When used as a switch, a transistor operates in two states: cutoff, where it blocks current and acts like an open switch, and saturation, where it conducts fully and acts like a closed switch with small voltage drop. Switching between these states lets a microcontroller control loads such as relays, motors, or LEDs.

Question 24

What is the difference between an NPN and a PNP transistor?

Accepted Answer

An NPN transistor turns on when current flows into its base, with collector current flowing into the collector and out of the emitter. A PNP transistor turns on when current flows out of its base, with all polarities and currents reversed. Choosing between them depends on which side of the load the switch sits.

Question 25

What is an operational amplifier, and what are its ideal assumptions?

Accepted Answer

An operational amplifier is a high gain differential amplifier that amplifies the voltage difference between its two inputs. Its ideal assumptions are infinite open loop gain, infinite input impedance, and zero output impedance, so the inputs draw no current and sit at the same voltage when negative feedback is applied.

Question 26

What is negative feedback, and why is it used in amplifiers?

Accepted Answer

Negative feedback routes part of an output signal back to an input so that it opposes the input change. It reduces gain but increases bandwidth, stabilizes the gain against component variation, and reduces distortion. Most practical amplifier circuits rely on negative feedback to make performance predictable.

Question 27

How do you calculate the gain of an inverting op amp amplifier?

Accepted Answer

For an inverting amplifier, the closed loop gain equals negative feedback resistor divided by input resistor, written as minus Rf over Rin. The output is inverted, meaning a positive input produces a negative output. The noninverting input is tied to ground, and the inverting input acts as a virtual ground because of negative feedback.

Question 28

How does a noninverting op amp amplifier differ from an inverting one?

Accepted Answer

A noninverting amplifier applies the input signal to the positive input, and its closed loop gain equals one plus Rf divided by Rg. Its output has the same polarity as the input, its input impedance is very high, and its gain can never be less than one.

Question 29

What is a low pass filter, and what determines its cutoff frequency?

Accepted Answer

A low pass filter passes signals below a chosen frequency and attenuates those above it. In a simple RC version, the cutoff frequency equals one divided by two pi times R times C. Active filters built with op amps can provide steeper rolloff, while passive filters need no power supply.

Question 30

What is the purpose of biasing a transistor amplifier?

Accepted Answer

Biasing sets the quiescent operating point, meaning the steady voltages and currents present when no signal is applied. Proper bias keeps the transistor in its active region across the full signal swing, preventing clipping and distortion. Common methods use a resistor divider on the base, an emitter resistor for stability, or feedback from the collector.

Question 31

What is common mode rejection ratio in a differential amplifier?

Accepted Answer

Common mode rejection ratio is a measure of how well a differential amplifier ignores signals that appear equally on both inputs. It is usually expressed in decibels as the ratio of differential gain to common mode gain. A higher value means the amplifier better rejects noise and interference picked up on both input wires.

Question 32

How does a voltage follower work, and what is it used for?

Accepted Answer

A voltage follower is an op amp configured with its output tied directly to the inverting input, giving a gain of exactly one. It provides a high input impedance and low output impedance, so it buffers a source from heavy loads. It is often used to isolate sensor outputs from downstream circuits.

Question 33

What are logic levels, and why do they matter in digital design?

Accepted Answer

Logic levels are the voltage ranges that a digital circuit interprets as a logical zero or one. Each family defines input and output thresholds, and a driver must output voltages that the receiver accepts. Mismatched levels can cause unreliable operation, so designers check thresholds when connecting different logic families.

Question 34

What is a pull up resistor and when is it needed?

Accepted Answer

A pull up resistor connects an input or open drain output to a positive supply, so the line rests at a defined high level until something actively pulls it low. It is needed on open drain or open collector outputs, and on inputs that might otherwise float. Its value balances speed against power use.

Question 35

Why are decoupling capacitors placed close to integrated circuit power pins?

Accepted Answer

A decoupling capacitor supplies brief current demands from the IC, so fast switching does not cause the supply voltage to sag or spike. Placing it close to the pin keeps the loop inductance low, because trace inductance limits how quickly current can arrive from a distant bulk capacitor. A larger bulk capacitor often supports the local decoupling capacitors.

Question 36

What is the purpose of a ground plane in a printed circuit board?

Accepted Answer

A ground plane is a large copper area that provides a low impedance return path for signal currents. It reduces noise, stabilizes reference voltage, and helps shield sensitive traces from interference. Return currents follow the path of least impedance, so a continuous plane beneath signal traces keeps loops small and predictable.

Question 37

How does trace width relate to current carrying capacity on a PCB?

Accepted Answer

Wider traces have lower resistance and can carry more current before heating excessively, so the required width depends on current, copper thickness, and allowed temperature rise. Designers use established charts or calculators, often based on published standards, to size traces. Thin traces may work electrically but overheat under sustained load.

Question 38

What is crosstalk, and how can layout reduce it?

Accepted Answer

Crosstalk is unwanted coupling of signal energy from one trace or wire into a neighboring one through capacitive or inductive effects. Layout reduces it by increasing spacing between aggressive and sensitive nets, keeping traces short, and routing adjacent signals orthogonally on different layers. A nearby ground or guard trace can also help.

Question 39

Why should a designer consider signal return paths when routing a PCB?

Accepted Answer

Every signal current needs a return path, and that current flows through the lowest impedance route, usually directly beneath the signal trace on an adjacent plane. If the return path is interrupted, for example by a split in the ground plane, the loop area grows and radiated emissions and noise increase.

Question 40

Why does a microcontroller system often need a reset circuit?

Accepted Answer

A reset circuit holds the processor in a known state while the supply stabilizes, then releases it so program execution starts from the beginning. Without it, the chip may start with undefined register values or erratic behavior during power up. Reset inputs often use a pull up resistor and a capacitor for delay.

Electronics Design Engineering Flashcards

1Circuit Laws and Power

2Passive Components and Behavior

3Semiconductor Devices

4Analog Amplifier and Filter Design

5Digital Logic and Board Layout

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