ECE006 Engineering College Quiz
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Questions and Answers

What is gain in electronics?

Gain in electronics refers to amplification, which is the ratio of output voltage to input voltage.

How is gain calculated in electronics?

Gain is calculated as the ratio of output voltage to input voltage.

What is attenuation in electronics?

Attenuation in electronics refers to the loss of signal amplitude as it passes through a circuit or component.

What is the formula to calculate decibels (dB)?

<p>Decibels are calculated using the formula: Gain (in dB) = 10 * log10(Output Power / Input Power).</p> Signup and view all the answers

How is attenuation represented mathematically?

<p>A = Output Voltage / Input Voltage</p> Signup and view all the answers

What is the power gain, in decibels, for an amplifier with an input of 90 mV across 10 kV and an output of 7.8 V across an 8-V speaker?

<p>28.9</p> Signup and view all the answers

If an amplifier has a power gain of 28 dB and the input power is 36 mW, what is the output power?

<p>29.45 mW</p> Signup and view all the answers

If a circuit has two amplifiers with gains of 6.8 dB and 14.3 dB, and two filters with attenuations of -16.4 dB and -2.9 dB, and the output voltage is 800 mV, what is the input voltage?

<p>1.12 V</p> Signup and view all the answers

Express the power level Pout = 12.3 dBm in watts.

<p>0.053 mW</p> Signup and view all the answers

What is the purpose of keeping leads very short in radio applications?

<p>To minimize the inductive and capacitive effects.</p> Signup and view all the answers

Which type of resistors have practically no leads except for the metallic end pieces soldered to the printed-circuit board?

<p>Film resistors</p> Signup and view all the answers

Metal film resistors are quieter than ______ resistors.

<p>carbon film</p> Signup and view all the answers

The resistance of a wire conductor is only determined by its ohmic resistance.

<p>False</p> Signup and view all the answers

Define a tuned circuit.

<p>A circuit made up of inductance and capacitance that resonates at a specific frequency.</p> Signup and view all the answers

What is the bandwidth of a resonant circuit with a frequency of 28 MHz and a Q of 70?

<p>0.4 MHz</p> Signup and view all the answers

Calculate the approximate resonant frequency of a resonant circuit with upper and lower cutoff frequencies of 8.07 MHz and 7.93 MHz.

<p>8 MHz</p> Signup and view all the answers

What are the approximate 3-dB down frequencies of a resonant circuit with a Q of 200 at 16 MHz?

<p>15 and 17 MHz</p> Signup and view all the answers

What is the impedance of a parallel LC circuit with a resonant frequency of 52 MHz and a Q of 12?

<p>Varies based on L, C, R, and W</p> Signup and view all the answers

What type of filter passes frequencies below a critical frequency called the cutoff frequency?

<p>Low-pass filter</p> Signup and view all the answers

What is the cutoff frequency of a single-section RC low-pass filter with R= 8.2 kΩ and C = 0.0033μF?

<p>15.29 Hz</p> Signup and view all the answers

What is the closest standard EIA resistor value that will produce a cutoff frequency of 3.4 kHz with a 0.047-μF capacitor in a high-pass RC filter?

<p>47 kΩ</p> Signup and view all the answers

What values of capacitors would you use in an RC twin-T notch filter to remove 120 Hz if R = 220kΩ?

<p>0.013 μF</p> Signup and view all the answers

What does Fourier analysis allow us to determine in complex signals?

<p>sine wave components and bandwidth</p> Signup and view all the answers

Define rise time in a pulse wave and its importance.

<p>Rise time is the time taken for the pulse voltage to rise from 10% to 90%, and it affects the bandwidth.</p> Signup and view all the answers

What is the rise time of an input square wave if the pulse train has a rise time of 6 ns?

<p>6 ns</p> Signup and view all the answers

Which of the following is an example of a time-domain waveform?

<p>Square wave</p> Signup and view all the answers

What is the purpose of band-reject filters?

<p>reject a narrow band of frequencies around a center or notch frequency</p> Signup and view all the answers

What advantages do active filters offer over standard passive LC filters?

<p>Easy to tune</p> Signup and view all the answers

What type of material is used to make filters that exhibit piezoelectricity? Use thin slivers of ________ or certain types of ceramic materials.

<p>quartz</p> Signup and view all the answers

Fourier analysis tells us that a square wave is made up of a sine wave at the fundamental frequency and an infinite number of odd harmonics.

<p>True</p> Signup and view all the answers

What happens to capacitive reactance as the frequency of operation increases?

<p>Decreases</p> Signup and view all the answers

As frequency decreases, how does the reactance of a coil vary?

<p>Increases</p> Signup and view all the answers

What is skin effect, and how does it affect the Q of a coil?

<p>Skin effect is the tendency of high-frequency current to flow near the surface of a conductor. It increases the effective resistance of the coil, thus decreasing its Q factor.</p> Signup and view all the answers

What happens to a wire when a ferrite bead is placed around it?

<p>It suppresses high-frequency noise and reduces electromagnetic interference.</p> Signup and view all the answers

What is the name given to the widely used coil form that is shaped like a doughnut?

<p>Toroid</p> Signup and view all the answers

Describe the current and impedance in a series RLC circuit at resonance.

<p>At resonance, the current is maximum and the impedance is minimum.</p> Signup and view all the answers

Describe the current and impedance in a parallel RLC circuit at resonance.

<p>At resonance, the impedance is maximum and the current is minimum.</p> Signup and view all the answers

State in your own words the relationship between Q and the bandwidth of a tuned circuit.

<p>The quality factor (Q) of a tuned circuit is the ratio of its bandwidth to its center frequency.</p> Signup and view all the answers

Explain how capacitance and inductance can exist in a circuit without lumped capacitors and inductor components being present.

<p>Capacitance and inductance can exist in a circuit through parasitic elements such as conductors, wires, or traces.</p> Signup and view all the answers

How can the voltage across the coil or capacitor in a series resonant circuit be greater than the source voltage at resonance?

<p>In a series resonant circuit, at resonance, the voltage across the coil or capacitor can become greater than the source voltage due to energy storage and reactive power exchange.</p> Signup and view all the answers

Explain why it is possible to reduce the effective Q of a parallel resonant circuit by connecting a resistor in parallel with it.

<p>Adding a resistor in parallel with a parallel resonant circuit increases the circuit's losses, decreasing its effective Q factor.</p> Signup and view all the answers

Study Notes

Here are the study notes for the provided text:

Fundamentals of Electronics

  • Gain refers to amplification, and the ratio of output to input voltage is called voltage gain (Av)
  • Voltage gain (Av) is expressed as: Av = Vout / Vin
  • Power gain (AP) is calculated as: AP = Pout / Pin
  • When cascading amplifiers, the overall gain is the product of individual gains

Attenuation

  • Attenuation refers to a loss introduced by a circuit or component
  • Attenuation (A) is expressed as: A = Vout / Vin
  • Circuits with attenuation have a gain less than 1
  • Total attenuation is the product of individual attenuations of each cascaded circuit

Decibels

  • Decibel (dB) is a unit of measurement that expresses the ratio of two values
  • Decibel is one-tenth of a bel
  • Decibel calculations: gain/attenuation in dB = 10 * log10 (output/input)
  • dBm: a decibel value referenced to 1 mW

Tuned Circuits

  • Tuned circuits consist of inductive and capacitive elements that resonate at specific frequencies
  • Inductive and capacitive elements offer an opposition to alternating current flow known as reactance

Reactive Components

  • Capacitors:
    • Oppose voltage changes across them
    • Capacitive reactance (XC) is inversely proportional to capacitance (C) and frequency (f)
    • XC = 1 / (2 * π * f * C)
  • Inductors:
    • Produce a magnetic field when current passes through them
    • Inductance opposes current changes in the coil
    • The basic unit of inductance is the henry (H)

Let me know if you'd like me to make any changes!### Inductance and Inductors

  • Inductance is affected by physical characteristics of the coil, including the number of turns, spacing, length, diameter, and magnetic core material
  • In a dc circuit, an inductor has little or no effect, only ohmic resistance of the wire affects current flow
  • In an ac circuit, the inductor opposes changes in current, known as inductive reactance (XL)
  • XL is expressed in ohms and is calculated using the expression XL = 2πfL
  • Stray capacitance between turns of the coil is like a small capacitor connected in parallel with the coil
  • At high frequencies, lead lengths should be kept short to minimize inductive reactance

Types of Inductors

  • Heavy self-supporting wire coils
  • Inductors made as copper patterns
  • Insulating forms
  • Toroidal inductors
  • Ferrite bead inductors
  • Chip inductors

Resistors

  • At low frequencies, a standard low-wattage color-coded resistor offers nearly pure resistance
  • At high frequencies, the leads have considerable inductance, and stray capacitance between leads causes the resistor to act as a complex RLC circuit
  • To minimize inductive and capacitive effects, leads are kept very short in radio applications
  • Tiny resistor chips used in surface-mount construction have virtually no leads and little stray capacitance

Skin Effect

  • The resistance of a wire conductor is primarily determined by the ohmic resistance of the wire
  • Skin effect is the tendency of electrons flowing in a conductor to flow near and on the outer surface of the conductor at high frequencies
  • Skin effect decreases the total cross-sectional area of the conductor, increasing its resistance and affecting circuit performance
  • Copper tubing and thin conductors are used to minimize skin effect

Tuned Circuits

  • A tuned circuit is made up of inductance and capacitance and resonates at a specific frequency
  • Tuned circuits are frequency-selective, responding best at the resonant frequency and a narrow range of frequencies around it
  • A series resonant circuit is made up of inductance, capacitance, and resistance, and resonates when the inductive and capacitive reactances are equal
  • The resonant frequency can be expressed in terms of inductance and capacitance: fr = 1/2π√LC

Series Resonant Circuits

  • The total impedance of the circuit is given by the expression Z = √R² + (XL - XC)²

  • At resonance, the total circuit impedance is simply the value of all series resistances in the circuit

  • The resonant frequency can be expressed in terms of inductance and capacitance: fr = 1/2π√LC

  • The bandwidth of a series resonant circuit is determined by the Q of the circuit: BW = fr/Q

  • The upper and lower boundaries of the bandwidth are defined by two cutoff frequencies, f1 and f2### Resonance and Impedance

  • When the reactances, resistances, and current are known, the voltage drops across each component can be computed.

  • At resonance, the voltage drops across the inductor and capacitor are significantly higher than the applied voltage, known as the resonant step-up voltage.

  • The voltage across the inductor leads the current by 90° and the voltage across the capacitor lags the current by 90°.

  • The inductive and reactive voltages are equal but 180° out of phase, resulting in a total reactive voltage of 0.

Resonant Circuits

  • Series resonant circuits: the voltage across the inductor and capacitor are in series with the source voltage.
  • Parallel resonant circuits: the inductor and capacitor are connected in parallel with the applied voltage.
  • At resonance, a parallel tuned circuit appears to have infinite resistance, draws no current from the source, and has infinite impedance.
  • The equivalent inductance (Leq) and resistance (Req) are calculated using the formulas: Leq = L/(Q² + 1) and Req = R(Q² + 1).

Quality Factor (Q)

  • Q is determined by the formula: Q = XL/R or Q = RP/XL.
  • A high Q indicates a high energy storage capacity and a narrow bandwidth.
  • Q is a measure of the circuit's ability to selectively respond to a particular frequency.

Filters

  • A filter is a frequency-selective circuit that passes some frequencies and rejects others.
  • There are four kinds of filters: low-pass, high-pass, bandpass, and band-reject filters.
  • Each type of filter has a specific frequency response and is used to achieve a particular filtering action.

Passive Filters

  • Passive filters use resistors, capacitors, and inductors to achieve the desired frequency response.
  • RC filters are widely used due to their simplicity and low cost.
  • RL filters are not as widely used due to the larger size and higher cost of inductors.

RC Filters

  • Low-pass filters: introduce no attenuation at frequencies below the cutoff frequency and completely eliminate all signals with frequencies above the cutoff.
  • High-pass filters: pass frequencies above the cutoff frequency and reject frequencies below the cutoff.
  • Band-reject filters: reject or stop frequencies over a narrow range but allow frequencies above and below to pass.
  • Notch filters: used to greatly attenuate a narrow range of frequencies around a center point.

LC Filters

  • LC filters are commonly used at radio frequencies due to their better selectivity.
  • Low-pass, high-pass, and band-pass filters can be implemented using LC filters.
  • The major types of LC filters are named after the person who discovered and developed the analysis and design method for each filter.

Types of LC Filters

  • Butterworth filters: have maximum flatness in response in the passband and a uniform attenuation with frequency.
  • Chebyshev filters: have extremely good selectivity and a high attenuation rate outside the passband.
  • Cauer (Elliptical) filters: produce an even greater attenuation or roll-off rate than Chebyshev filters and greater attenuation out of the passband.
  • Bessel filters: have a flat group delay, meaning that the phase shift or time delay introduced by the filter is constant across the passband.

Ripple

  • Ripple is the amplitude variation with frequency in the passband, or the repetitive rise and fall of the signal level in the passband of some types of filters.
  • Ripple is usually stated in decibels and can be present in the passband and stopband of some filters.

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A quiz for ECE students at Nueva Vizcaya State University, covering topics in engineering and electronics.

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