AC Circuit Final Exam Review questions with 100% correct answers.docx, Exams of Biology

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AC Circuit Final Exam Review questions and answers T/F: Current exists in an ideal capacitor only when its voltage is changing - answer True T/F: In a series capacitor circuit, the largest value of capacitance will have the smallest amount of voltage dropped across it. - answer True T/F: In a series capacitor circuit, the largest value of capacitance will have the largest share of total charge on its plates - answer False T/F: Magnetic lines of force never cross one another - answer True T/F: Current flowing through a conductor creates a magnetic field that is concentric about the conductor - answer True T/F: The stacking factor for practical iron cores is always greater than unity - answer False T/F: The equation BW= w/Q applies to both series and parallel resonant circuits - answer True A capacitor consists of two metal plates separated by a(n) ___ material - answer dielectric The value of capacitance is ___ proportional to the area of the plates and ___ proportional to the spacing between the plates - answer directly; inversely The strength of an electric field is determined by the ___ of the lines of force - answer density Because no insulator is perfect, there is always a small amount of ___ current through the dielectric of a charged capacitor - answer leakage Voltage cannot change instantaneously across a capacitor, but ___ can change instantaneously across a capacitor - answer Current In the equation r=RC, r represents the ___ of the circuit expressed in units of ___ - answer Time constant; seconds In 5 time constants, a transient reaches approximately ___% of its final value - answer 100 In the equation Vc=V0e^-t/RC, Vc=___ when t=0 and Vc=___ when t>5RC - answer V0; 0 PRR and PRF are abbreviations for ___ and ___ - answer Pulse Repetition Rate; Pulse Repetition Frequency The rise time of a pulse waveform is measured to ___% amplitude, and the fall time to ___% amplitude - answer 90; 10 For a non-ideal square wave, pulse duration is measured at the ___% level - answer 50 The direction of flux external to a bar magnet is from the ___ pole to the ___ pole - answer North; South The SI unit of measure for flux is the ___ - answer Weber In the CGS system, flux is measured in units of ___ and flux density in units of ___ - answer Maxwells; gauss In the English system, flux is measured in units of ___ and flux density in units of ___ - answer Lines; lines/in^2 Tables that show the dielectric constant of various materials usually indicate ___ values - answer Relative The direction of an electric field is ___ - answer From the positive charge to the negative charge E=F/Qt expresses the fact that ___ - answer Electric field intensity is proportional to the force exerted on test charge, and inversely proportional to the amount of test charge F=k(QQt)/r^2 is a statement of ___ - answer Coulomb's law Normal capacitor leakage can be modeled as ___ - answer A very large value resistor connected in parallel with an ideal capacitor When the value of a capacitor increases with increasing temperature, it is said to have a positive ___ - answer Temperature coefficient In a series capacitor circuit, the total capacitance is ___ - answer Smaller than the smallest individual capacitor value In a series capacitor circuit, the ___ is always the same for each capacitor, and in a parallel capacitor circuit the ___ is always the same for each capacitor - answer Charge; voltage A 0.022-µF capacitor has a tolerance of ±10%. Determine the minimum and maximum allowable values - answer 0.020 µF; 0.024 µF A 22-µF capacitor has a tolerance of +12% and -8%. Determine what its minimum and maximum values might be - answer 24.6 µF; 20.2 µF Determine the amount of voltage that must be applied to 10 µF of capacitance in order to have a charge of 1.2 mC (Q=CV) - answer 120 V Four capacitors are connected in parallel across a 100-V source. The total charge is 250 µC, and three of the capacitors have identical values of 0.15 µF. What is the value of the fourth capacitor? (Q=CV) - answer 2.05 µF In a parallel capacitor circuit, C1=1.2 µF, C2=0.8 µF, and C3= 1.0 µF. Determine the value of C4 to be added in parallel to get a total capacitance of 4 µF. (Ctotal = C1+C2+C3+C4) - answer 1 µF The voltage applied to a 1.0-µF capacitor is changing at the rate of 1000 V/s. Determine the capacitor current. (ic=C(dv(t)/dt) - answer 1 mA Determine the current and voltage at 50 µs. - answer ic=11.4 mA; vc=5.85 V The transient in a series RC circuit with C=40 nF is 600 µs. What is the value of R? - answer 15 kΩ Determine the period of a pulse train that has a PRR of 1000 pps. (T=1/PRR) - answer T=1 ms A magnetic field is a(n) ___ field - answer Force When there is no core material present, the magnetic field produced by a current is ___ - answer Proportional to the current In a series magnetic circuit ___ - answer Flux is the same in all sections Structures to guide and shape magnetic fields are called ___ - answer Magnetic circuits A semiconductor device that develops a voltage proportional to magnetic field strength is called a ___ device - answer Hall effect Determine flux density where 500 µWb of flux is confined to an area of 2x10^-3 m^2. (B=Φ/A) - answer 0.25 T Given A=1.5 cm x 0.75 cm and B = 1 T, determine Ψ in Wb. (A*B) - answer 113 µWb The cross-section of a magnetic core measures 20 mm by 15 mm. If the magnetic density is 2.5 T, determine the amount of flux. (Φ=B⋅A - answer 750 µWb A magnetic field is being generated by a current of 1.2 A flowing through 100 turns of wire on a core having a reluctance of 200,000 At/Wb. Determine the flux of the circuit. (Φ=N⋅I/R) - answer 600 µWb If the flux linking a 100-turn coil changes at the rate of 4 Wb/s, what is the voltage across the coil? - answer 400 V The flux in an 80-turn coil decreases steadily from 0.75 Wb to 0.72 Wb in 100 ms. Determine the amount of induced voltage. (EMF=−N(ΔΦ/Δt)) - answer 24 V Determine the value of an inductor where a 200 A/s change in current causes a self- induced voltage of 10 V (VL=L(di/dt) - answer 50 mH Tests show that a current change of 0.12 A/ms causes 30 V to appear across an inductor. What is the value of the inductor? - answer 250 mH A voltage sine waveform has a peak Em=10 V and a frequency of 400 Hz. Determine the time at which e=5 V (e(t)=Emsin(2πft)) - answer 208 µs In a purely resistive circuit, the current and voltage phasors are ___ - answer 0 degrees out of phase In a purely inductive circuit, current ___ - answer lags the voltage by 90 degrees In a purely capacitive circuit, current ___ - answer Leads voltage by 90 degrees Doubling the frequency that is applied to an inductor ___ - answer Doubles the reactance Doubling the frequency that is applied to a capacitor ___ - answer Cuts the reactance in half Determine QL in a purely inductive circuit where V=100 V and XL=10 Ω - answer 1kVAR Cite the mathematical symbols used for (a) flux and (b) flux density - answer Φ; B Given A=20 cm^2, Ψ=0.5x10^-3 Wb, H=1650 At/m, N=200 turns, and l=20 cm. Determine B, F, and I (B=Ψ/A) (I=(HN/l) (F=B⋅I⋅l) - answer B=0.25 T; F=825 N; I=165 mA