Big ole test
What is generated when the magnetic field around an inductor collapses?
+An opposing voltage called counter electromagnetic force (cemf) that is proportional to the rate of the changing current. Complete flux loops around the whole coil and a flux pattern like a bar magnet.
What does a filter with enhanced flatness across the top, and sharpness at the edge of the bandwidth passed by the filter contain?
+Multiple resonant circuits.
When a circuit has several inductors, how is the total inductive reactance calculated?
+The same way the total resistance of resistors in a circuit is determined. By multiplying the inductive reactance of each inductor.
Where does a distribution amplifier module receive the direct current (DC) required for operation?
-From a coaxial cable that transports DC voltage from a network power supply. -From a rechargeable 12-volt battery in the station housing lid.
How else can a capacitance of 243 nanofarads (nF) be expressed?
0.243 microfarads (µF).
Velocity of propagation (VOP) is the speed of the radio frequency (RF) signals traveling in a coaxial cable relative to the speed of light. What is the range of VOP factors for broadband coaxial cable?
0.78 to 0.93
In addition to fines for noncompliance with leakage rules, what band of frequencies used by broadband cable operators can be shut down until the signal leakage is repaired?
108-137 MHz.
If the leakage detector indicates there is a leak and displays a reading of 14 microvolts per meter (uV/m) measured at 80 feet from a possible leak source, what is the approximate calculated level of the leak from 10 feet?
112 uV/m.
What is the value of the current in a resistive alternating current (AC) circuit when: (1) the effective voltage is 120 volts; (2) the resistance of the source is 3 ohms; (3) the resistance of the conductors is 2 ohms; and (4) the resistance of the load is 5 ohms?
12.0 amperes
To transport electric power efficiently, what power line voltage-current combination would deliver the same amount of power as 10 amps and 10,000 volts, but with the least conductor loss?
2 amperes and 50,000 volts.
If the attenuation through a span of coaxial cable at 75 MHz is 2.5 dB, what will be the approximate attenuation at 300 MHz?
2 x 2.5 dB, or 5.0 dB. 3 x 2.5 dB, or 7.5 dB. 5 x 2.5 dB, or 12.5 dB.
The Federal Communications Commission (FCC) requires that signal leaks of what intensity and greater must be logged and repaired?
20 microvolts per meter (µV/m), 3 meters from the leak.
What is the attenuation through 1,600-feet of 0.750 cable at 600 MHz and 120° F, when at 68° F and 600 MHz the cable attenuation rate is 1.31 decibels (dB)/100 feet? (Be sure to factor in the higher temperature.)
22.05 dB
What is the power loss in coaxial cable when: (1) the current flow through the coaxial cable is 5 amperes; (2) the coaxial cable loop resistance is 0.9345 ohms; and (3) the alternating current (AC) power source has an effective voltage of 60 volts?
23.36 watts.
What is the typical gain of a line extender in decibels (dB)?
28 to 35 decibels (dB).
What is the average value of a 10 volts peak-to-peak sine wave?
3.18 volts. 3.54 volts
In a silicon bipolar junction transistor (BJT) common emitter amplifier circuit, what should the base voltage be when the amplifier is forward biased?
3.7 volts above or below the emitter voltage, depending on whether it is an NPN or PNP transistor. 0.7 volt above or below the emitter voltage, depending on whether it is an NPN or PNP transistor.
In a network design map, the squares with the number inside are symbols for what devices?
4-port distribution taps.
How much intermodulation distortion degradation is added when two line extender amplifiers with identical distortion characteristics are in cascade?
6 decibels (dB).
Which sine wave frequency has the shortest wavelength?
750 megahertz (MHz).
What is the voltage into the second amplifier in cascade, if each amplifier draws 1.5 amps of current, the loop resistance of each section of cable is 1.38 ohms, and the alternating current (AC) source is a 90 volts AC (VAC) network power supply?
90 VAC.
When drawn as a resistive alternating current (AC) circuit, most hybrid fiber/coax (HFC) networks are what?
A combination of equipment powered in series and in parallel.
Shorts in the coaxial cable and excessive amounts of current can damage the distribution amplifier. Several devices can be used to protect the distribution amplifier from these problems. Which device shorts to ground when an overvoltage situation occurs?
A fast transfer electronic crowbar (FTEC).
Which type of rectifier circuit uses two alternating current (AC) waveforms on the transformer secondary?
A full-wave rectifier with a center-tapped transformer secondary.
What type of map can be useful for tracking the progress of a network upgrade, or the expanse of a network condition, such as an outage?
A network key map.
Which type of capacitor is likely used in a low frequency alternating current (AC) circuit where the maximum breakdown voltage is from 200 volts to 1,600 volts?
A paper capacitor.
Which type of capacitor is constructed like a paper capacitor but with a different dielectric, and is available with either axial or radial leads?
A plastic-film capacitor
What forces alternating current (AC) to flow through a circuit?
A polarity changing voltage.
At temperatures above absolute zero in silicon, what fills the location of electrons knocked out of their stable orbit by thermal effects?
A positive charge called a hole.
How much does a power inserter impact the radio frequency (RF) in a network?
A power inserter should have minimal impact on the RF in both directions.
Which type of diode utilizes the junction capacitance across a reverse-biased diode?
A rectifier diode.
How does encrypting all the digital TV (DTV) channels and service tiers defend against passive pirates?
A set-top box (STB) or TV with an authorized CableCard assigned to the customer account is required for reception.
What is a metallic time domain reflectometer (MTDR)?
A test instrument that measures reflected voltage at discrete moments in time to evaluate the electrical characteristics of metallic cables.
What do all hardline splitter, directional coupler, power inserter, and distribution tap housings have on the back?
A threaded mounting tap and strand clamp on the back for attachment to the aerial strand or an underground pedestal.
What is the advantage for supplying alternating current (AC) to multiple amplifiers from one network power supply?
Allows the designer to place amplifiers without concern about access to electrical utility power.
Which form of fluctuating direct current (DC) is a symptom of a malfunctioning DC power supply in hybrid fiber/coax (HFC) amplifiers and fiber nodes?
Alternating current (AC) ripple.
Why is it unnecessary to measure the unregulated direct current (DC) voltage on a line extender that has a switching mode power supply (SMPS)?
An SMPS provides DC voltage regulation over a wider alternating current (AC) voltage range than a linear power supply.
What can cause a resistive type of test to deliver false information?
An impedance mismatch.
What must be added to a light emitting diode (LED) to make it a Fabry-Perot (F-P) laser?
An interferometer, consisting of a mirror on one side of the laser diode and a partially-reflecting mirror on the other side.
For an application where it is undesirable to have electrical conduction (continuity) between an input and an output, what component would be used?
An opto-isolator.
What is 1 time constant (1T) of a capacitor?
Approximately 63% of the source voltage, the product of the of circuit resistance (R) and the capacitance (C) of the capacitor (R x C).
What are two uses of positive, intrinsic, negative (PIN) diodes?
As variable radio frequency (RF) resistors and fast RF switches.
Why was the impedance for the broadband cable industry standardized at 75 ohms (Ω)?
At 75 Ω characteristic impedance, the coaxial cable has minimal attenuation, with adequate breakdown voltage and power carrying capacity.
When splicing equipment into underground hardline coaxial cable, if the construction crew forgets to identify the direction of the cable, what can be done to find which cable attaches to the input and output side of the equipment?
Attach a cable locator to each cable to identify the route that each buried cable follows.
What type of filter is used in channel to traps to block some frequencies from arriving at the customer premises?
Band-stop filters.
What is a priority in any standby power supply maintenance program?
Battery care.
Why is the circuit impedance dependent on the alternating current (AC) frequency?
Because the capacitive and inductive reactance vary with the AC frequency.
When using a cable locator, why is it unnecessary to disconnect the cable from any connections?
Because the locating signal is carried on the cable shield.
What is a cable network best practice that can reduce the damage and danger of lightning to both property and life?
Bonding and grounding of the cable network.
What is the purpose for distribution amplifiers in a hybrid fiber/coax (HFC) network?
Boost the downstream signals before being divided and circulated throughout neighborhoods in the coaxial cable portion of the network.
How does surge protection at the input and output of a ferroresonant power supply defend against voltage surges?
By passing voltage surges (within the surge device rating) to ground without damage.
What is the ratio of the charge transferred between the capacitor plates to the potential difference between the plates?
Capacitance
Why is the total capacitive reactance of a network of capacitors connected in parallel calculated by adding their reactance together like a series of resistors?
Capacitors in parallel act like one large capacitor whose plate area is equal to the sum of the conductive plate areas of the individual capacitors.
What does allowing current to flow in only one direction enable the diode to do?
Change alternating current (AC) to direct current (DC).
How does a time domain reflectometer (TDR) measure the distance to a reflection from a fault or the end of a cable?
Circuitry within the TDR converts the pulse travel time into distance and displays the information as a waveform with a scale showing the distance to the reflection.
Where is a clamp-on ammeter attached to measure the output current from a network power supply?
Clamped around one of the conductors going to cabinet indicator lamp.
If the hardline coaxial cable center conductor is too short after coring the dielectric with a combination coring tool, what should be done?
Clean out any dielectric and aluminum trimmings from the cable and the tool and continue coring to the correct depth.
Which element likely has distributed capacitance?
Coaxial cable
If all conductors have inductance, why are inductors typically coiled conductors?
Coiled conductors link the magnetic field between the coil loops, increase the inductance, and enable packaging of the conductor into a smaller space.
Which is a benefit of an aggressive signal leakage policy?
Decreased ingress-related service calls.
What is another name for the bipolar junction transistor (BJT) common collector configuration?
Emitter follower.
In hardline coaxial cable, what is the most common dielectric material?
Foamed polyethylene produced by gas injection.
In which application would a bipolar junction transistor (BJT) common base configuration be used?
For impedance isolation between a low-impedance device and high-impedance amplifier.
When setting up the forward amplifier of a line extender, why must the manual gain control be at a mid-range position at the desired operating level?
For the automatic/thermal control to work effectively.
What are the terminals called in a junction field effect transistor (JFET)?
Gate, source, and drain.
What property of a filter with inductors (L) and capacitors (C) can stretch and distort digital TV data pulses, making it difficult for the receiver to recover the signal?
Group delay.
Intended to reduce disruption of service to customers, what area should be the priority for preventive maintenance?
Headend equipment and signals originating in the headend that go to all customers are considered the most critical.
What should be used in place of short coaxial cable jumpers to provide a compact and solid mechanical and electrical connection between the equipment housings?
Housing-to-housing adapters.
When can a single straight splice connector be used to repair a crack in aerial hardline coaxial cable?
If the crack is small, water migration is minimal, and the crack is in a straight section of cable.
What is the counter electromotive force (cemf) reaction that opposes a change in current flow through an inductor is called?
Inductive reactance.
What is the opposition to alternating current above the resistance of the inductor to direct current (DC) called?
Inductive reactance.
Which of the following problem(s) are caused by egress from a hybrid fiber/coax (HFC) network?
Interference with aeronautical navigation and communication, amateur radio, public service, and cellular communications.
Which of the following describes a power inserter?
It contains a high-pass filter network that passes radio frequency (RF) signals between the two RF/alternating current (AC) ports and blocks the 60-hertz (Hz) AC voltage between the same two ports.
Which characterizes a feed-through distribution tap?
It has a directional coupler that efficiently routes most of the signal to the output port while removing a small amount of the signal and passing it to the splitter network.
What does a thermal control circuit in a distribution amplifier do?
It maintains the amplifier output levels as the input levels vary with temperature changes.
When looking at a design map, what do the small circles with an X connected with a solid line represent?
Joint use poles.
What leakage level must be entered in the leakage log?
Leaks 20 microvolts per meter (μV/m) or higher measured 10 feet from the cable.
Line extenders can be powered from the network or from a 120- volts alternating current (VAC) source. Which of the following statements about line extender power sources is true?
Line extenders powered by the network can pass current to other devices.
What characteristic of ferrite allows its use as core material in radio frequency (RF) applications?
Low electrical conductivity for less internal power loss at RF than other iron-core transformers.
What enables a transformer to transfer electrical energy from circuit to another?
Mutual inductance
What is the induction of electromotive force (emf) into an inductor from the changing magnetic field lines around another inductor that encircle, or link, the turns of the inductors called?
Mutual inductance.
The Occupational Safety & Health Administration (OSHA) requires the cable operator to provide its field workforce regular safety training on which topics?
None, OSHA defers to the cable operator's insurance carrier to determine what training is relevant, necessary, and appropriate for their employees. Topics that reinforce the operator's commitment to employees about safety in the workplace.
In a directional coupler, what is the relationship of the insertion loss between the directional coupler input and through ports, and the amount of signal tapped off from the input?
None, the insertion loss is independent of the signal tapped from the input.
What advantage is realized by increasing the voltage in a broadband cable network from 60 volts alternating current (VAC) to 90 volts?
Operating with 50% more voltage reduces the voltage drop and current drawn in the network for more efficient power utilization.
Where is the density of eddy currents in a conductor the greatest, causing the skin effect?
Outside the magnetic field rings on the outside of the conductor. Inside the magnetic field rings in the central part of the conductor.
What type of adapter is used for permanent or temporary jumper installation in place of damaged hardline coaxial cable or equipment hookup?
Pin-to-F female adapter
What element in a splitter and directional coupler serves, among other functions, to determine to which ports 60/90 alternating current voltage (VAC) is sent?
Plug-in fuses.
What is used to select which distribution amplifier secondary downstream output ports are active and whether they have equal or unequal output levels?
Plug-in modules or jumpers.
As the RF signal travels on the coaxial cable, one portion of the signal may be attenuated more than the others. What term is used to describe a situation where cable attenuation is low, causing signal levels to remain greater at the higher frequencies than at the lower frequencies?
Positive tilt
What is a consequence of high-speed charging and discharging of the capacitance in a complementary metal oxide semiconductor (CMOS)?
Power is dissipated as heat.
What are the three most common components of an atom and where are they located in the atom?
Protons and neutrons are located in the nucleus of the atom and electrons are located in orbit around the nucleus.
Because field employees are frequently working without supervision, what must cable operators do to remind and help employees make the safest decisions?
Provide safety training regularly.
What could a light dimmer with a silicon controlled rectifier (SCR) create in a customer premises?
Radio frequency interference (RFI). Efficient dimming of lights during a full power cycle.
When trying to find the source of a very strong leakage signal, what should be done?
Reduce the sensitivity of the leakage detector or even remove the antenna and allow the connector alone to pick up the leakage signal.
What should be done before measuring any distance with a measuring wheel?
Set the measuring wheel distance counter to zero.
A return path sweep-and-alignment system is used to adjust which of the following?
Signals from a line extender to the headend.
What happens when there is an impedance mismatch between the coaxial cable and the load?
Some signal energy is transferred to the load, with the remainder reflected along the coaxial cable back to the source.
There are many ways that broadband cable signals can be "pirated," or taken without compensation to the cable operator. Which of the following is an example of passive piracy?
Someone moves into an apartment and broadband service is already active without establishing an account.
When troubleshooting signal leakage in the drop system, what does it mean if all signs of signal leakage disappear when the ground block is disconnected and terminated on the side connected to the customer premises?
Something in the customer premises is the leakage source.
Which hardline coaxial cable splicing project would be in the repair and/or maintenance category?
Splicing in a short replacement cable with a straight splice connector.
What must be done when measuring the port-to-port isolation between the output ports of a splitter or directional coupler?
Terminate the common input port.
How does the power waveform of a resistive alternating current (AC) circuit compare to the voltage and current sine waves?
The AC power waveform has two positive half-cycles and two positive peaks.
What is the difference between a digital multimeter (DMM) that measures and displays average alternating current voltage (ACV) and true root mean square (RMS) DMM?
The DMM that measures and displays average ACV that is approximately 10% lower than what is present and displayed by a true RMS DMM.
The Proactive Network Maintenance (PNM) specification is defined in what other specification?
The Data Over Cable Service Interface Specification (DOCSIS).
What inserts alternating current (AC) into the network with a direct connection to an amplifier rather than using a power inserter?
The amplifier AC circuitry.
According to the Federal Communications Commission (FCC) leakage regulations, what distance must an antenna be from the network for leakage level measurements?
The antenna must be 3 meters (10 feet) from the network elements and 3 meters (10 feet) above the ground.
When using a single-purpose coring tool, what is done before the coring tool can be used to cut and remove the dielectric?
The appropriate length of aluminum shield and dielectric must be removed, to expose the cable center conductor.
What is the bandwidth of a resonant circuit?
The band of frequencies between the 70.7% points of the voltage curve for parallel resonant circuits or the current curve for series resonant circuits.
In a standby network power supply, what comes online to convert the battery voltage to alternating current (AC), which then goes to the ferroresonant transformer?
The battery-powered inverter.
In a half-wave power supply, what enables voltage to be provided to despite current flow through the diode stopping?
The capacitor across the load.
What happens when alternating current (AC) is applied to an inductor?
The changing polarity AC source current is continually opposed by the inductor counter electromotive force (cemf) current.
Compared to direct current (DC), what does the skin effect do to the cross-sectional area and alternating current (AC) flow capacity of the conductor?
The cross-sectional area and AC flow capacity of the conductor remain the same. The cross-sectional area and AC flow capacity of the conductor are reduced.
For the power in the primary and secondary windings of a transformer to remain equal, what must the current in the secondary windings do when the voltage is stepped up?
The current in the secondary windings must step down in proportion to the voltage increase.
In a resistive alternating current (AC) with all the resistance in series, what is known?
The current through all the resistance is the same.
Near the junction of the P-type and N-type regions, the free electrons on the N-side move across the junction to the P-side, and the holes on the P-side cross over to the N-side. What prevents any further flow of free electrons and holes?
The depletion region.
What is the return loss in coaxial cable?
The difference in decibels (dB) between the signal power applied to a terminated cable and the reflected signal power.
When using the triangulation technique to find the source of a leak, why is a dipole antenna used?
The dipole antenna is directional and picks up the strongest signal that is at a right angle, or perpendicular to the antenna elements.
What is the sine wave phase angle?
The distance in degrees from the 0° reference point to any other point on the waveform.
How can a distribution amplifier be identified in the network or on a network design map?
The distribution amplifier has multiple downstream outputs.
Unless specified otherwise, what does I = E/R for a resistive alternating current (AC) circuit is assumed to mean?
The effective value of the current (IEFF) equals the effective value of the voltage (EEFF) divided by the resistance (R).
What is on the interior side of the faceplate in a hardline splitter, directional coupler, power inserter, and distribution tap?
The electronic circuitry and male or female faceplate/housing interconnect pins.
What limits the number of colors from light emitting diodes (LED)?
The elements that can be used for LED dopants and their energy levels.
What is a consequence of cutting hardline coaxial cable with conventional side cutters?
The end of the cable is crushed and deformed, which makes coring the dielectric and sliding connector parts onto the cable difficult.
Anomalies, such as echoes and blind spots, can hide cable faults or cause a technician to misinterpret the signature of a time domain reflectometer (TDR) waveform. What causes an echo on a waveform TDR?
The extra distance that the TDR pulse travels after initially reflecting off the end of the cable span.
What type of adapter provides a clean transition from the hardline coaxial cable to an F-connector when testing hardline coaxial cable with a time domain reflectometer (TDR)?
The hardline cable-to-F female (or BAFF) adapter.
What units are used to express inductance?
The henry (H).
When studying a network map for an upcoming splicing project, how can you identify the high-output port of an unbalanced 3-way splitter ?
The high-output port of an unbalanced 3-way splitter is indicated by a dot on the map symbol.
What is the relationship of the inductive reactance of an inductor and frequency?
The higher the frequency, the higher the inductive reactance. The inductive reactance remains the same at all frequencies.
When opening a distribution amplifier station housing, why is it usually unnecessary to loosen the bolts at the bottom of the housing?
The housing lid is usually attached to the base of the housing with hinges.
What is done for leak measuring 1.25 microvolts per meter (μV/m) from about 160 feet away from the coaxial cable network?
The leak level is likely 20 μV/m or higher when measured 10 feet from the cable and must be fixed and recorded in the leakage log.
When calculating the network cumulative leakage index (CLI), what is done with leaks that are equal to or greater than 50 microvolts per meter (µVm) measured 10 feet from the network?
The leakage values are added together, then multiplied times a factor based on how much of the network was tested in 90 days.
What presents the biggest electrical shock hazard when operating a time domain reflectometer (TDR) in the network?
The low-frequency alternating current (AC) voltage on the coaxial cable.
Which part of a ferroresonant transformer regulates the load on the secondary winding?
The magnetic shunt.
In a resistive alternating current (AC) circuit, what is the magnitude of the current directly proportional to when the resistance remains the same?
The magnitude of the voltage.
What is the peak value of a sine wave?
The most positive or most negative level of each sine wave half cycle.
What happens when you apply the direct current (DC) voltage of a battery to the conductive plates of a capacitor?
The plate connected to the positive battery terminal receives a negative charge.
What is inductance?
The property by which voltage and current is induced into a circuit by a changing magnetic field.
In a resonant circuit, what property is adjusted to achieve the desired bandwidth?
The quality factor (Q).
What is a characteristic of the quasi-square wave produced by the ferroresonant transformer in hybrid fiber/coax (HFC) network power supplies?
The quasi-square wave edges become more rounded as the load increases.
What is the coaxial cable velocity of propagation (VoP)?
The rate that radio frequency (RF) signals travel through the coaxial cable versus the speed that RF signals travel in a vacuum or free space.
What does the decibel return loss (dBRL) displayed on most time domain reflectometers (TDR) indicate?
The relative severity of a cable fault.
What can be done when installing hardline splitters, directional couplers, power inserters, and distribution taps in tight quarters, such as in a pedestal?
The seizure screw can be removed, and the hardline connecter attached to the side of the housing.
What is the RF distribution tap value indicated on the tap face plate by a sticker or number stamped into the housing?
The signal loss between the tap downstream input port and the tap ports.
What defines the period of a sine wave?
The time that it takes for completion of one cycle of the signal.
Which statement about a forward-biased silicon diode is true?
The voltage drop across the diode is approximately 0.7 volt.
What do you call the maximum voltage that a given capacitor can handle?
The working voltage
What characteristics about upstream signals from cable modems and set-top boxes (STB) make them impractical for verifying and aligning a distribution amplifier return section?
They are of short duration and originate from various locations.
What is a desirable feature of Schottky barrier diodes?
They have a lower voltage drop than silicon diodes.
In addition to being less expensive than cable with a solid copper center conductor, what other benefit does a steel or aluminum conductor core provide?
They reduce the magnitude of the eddy currents and skin effect on the conductor.
How does a distribution amplifier in a fiber node receive the downstream radio frequency (RF) signals?
Through a coaxial cable that is connected to the downstream optical receiver.
How can signal leaks (egress) from hardline coaxial cable occur?
Through cracks in the shield where the cable is bent, or tiny holes in the shield.
How is the alternating current (AC) voltage from a generator accessed?
Through slip rings that maintain physical contact with stationary brushes that can be connected directly to a circuit.
In aerial installations, why do cable manufacturers recommend that expansion loops be formed in hardline coaxial cable?
To allow movement of the cable when lashed to the strand.
Why are many network design maps drawn on a scale in which 1 inch represents 100 feet, a ratio of 1:1,200?
To comply with the standard scale of road maps.
How is a time domain reflectometer (TDR) used during a tap audit or when investigating a suspicious network connection?
To confirm an illegal connection of customer premises equipment (CPE) based on the signature of the TDR waveform.
Why would a technician be asked to measure the signal levels on the highest and lowest downstream channels from a specific location when performing a cost payback analysis?
To help the design group determine where to add distribution taps, or to tap into the network for a network extension.
Why is it necessary that feed-through distribution taps pass alternating current (AC)?
To pass AC along to power other amplifiers downstream.
In a power inserter with three filtering networks, what is the purpose of the high-pass filter?
To prevent the 60 hertz (Hz) alternating current (AC) from passing between the two radio frequency (RF)/AC ports.
What is the purpose of a back-facet diode in an optical transmitter?
To sense the light level being put out by the diode.
Why is there a diplex filter at each downstream output port in a distribution amplifier?
To separate the downstream radio frequency (RF) from the upstream RF signals.
Pin-to-pin splice, or in-line splice block
Two different size cables with pin connectors attached.
Why is it a good practice to measure the downstream input signal and compare the measurements to the calculated levels shown on the network maps before attempting to set up the forward amplifier section of a line extender?
Undocumented changes to the network design can affect the designed input to the line extender, or there could be a separate problem that needs to be corrected.
What is the basic amplifier application that increases the amplitude of the radio frequency (RF) signal to compensate for the signal loss of cable and passive devices preceding the amplifier called?
Unity gain.
When aligning amplifiers in the return path, what must be achieved and maintained from the customer premises to the headend, or node?
Unity gain.
How do you obtain the simplest form of capacitance?
Using two parallel metal plates separated by an insulator.
Why does it appear that a capacitor passes alternating current (AC), but blocks direct current (DC)?
With an AC source, the capacitor continuously charges and discharges for current flow in the same direction, appearing to pass through the capacitor.
How does capacitive reactance oppose a changing applied voltage?
With energy that is temporarily stored in an electric field.