Electronics Information · Practice test 4

Correct answer: the frequency of the supply rises

An inductor fights change in current, so the faster the current alternates the harder it pushes back, and reactance rises with frequency. At zero frequency, meaning DC, an ideal coil offers no reactance at all.

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Correct answer: 18 ohms

Resistances in series simply add, so 6 + 6 + 6 = 18 ohms. The choice 2 ohms is what the same three resistors would give in parallel.

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Correct answer: decrease

Each new branch is another route for current, and more routes means less overall opposition. It is why plugging too many appliances into one circuit draws more current and can trip the breaker.

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Correct answer: Four

A bridge arranges four diodes so that both halves of the AC cycle are directed the same way through the load. A single diode gives half-wave rectification, wasting half the cycle.

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Correct answer: an insulator

An insulator's electrons are tightly bound to their atoms, so very little current flows through it even under high voltage. Rubber and glass are common examples.

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Correct answer: 0.5 amperes

Rearranging the power formula, current equals power divided by voltage, so 60 / 120 = 0.5 amperes. Dividing voltage by power gives 2, the reversed answer.

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Correct answer: many components built onto a single chip

An integrated circuit packs transistors, resistors, and their connections onto one piece of semiconductor, which is how a whole processor fits on a fingernail.

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Correct answer: conducts electricity slightly better than copper

Silver has the lowest resistivity of any metal, making it the best natural conductor, though its cost limits its use to specialized contacts and plating.

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Correct answer: a difference between the current leaving and returning on its monitored wires

The device continuously compares outgoing and returning current on the circuit it protects. Any imbalance means current is leaking somewhere else, possibly through a person, and it cuts power almost instantly.

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Correct answer: reduces voltage from primary to secondary

A step-down transformer has fewer turns on the secondary coil than the primary, so the output voltage is lower. Current rises correspondingly, since a transformer changes voltage rather than creating power. Transformers work only on AC and never change frequency.

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Correct answer: 0.001 ampere

The prefix milli means one thousandth, so a milliampere is 0.001 ampere. Kilo means one thousand times, moving in the opposite direction.

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Correct answer: open, or blown

An infinite resistance reading means no path exists for current, which is exactly what happens when a fuse's element has melted and broken the circuit.

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Correct answer: out of phase with one another

Phase describes the timing relationship between waveforms of the same frequency. Two in phase peak together; any offset in timing between their peaks means they are out of phase.

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Correct answer: a battery

The long line marks the positive terminal and the short line the negative, and repeating the pair shows several cells. A resistor is drawn as a zigzag or a plain rectangle.

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Correct answer: decrease to about half its former value

Resistance is inversely proportional to a conductor's cross-sectional area, so a thicker wire of the same length and material offers proportionally less opposition to current.

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Correct answer: an electric field between its plates

A capacitor holds opposite charges on two plates separated by an insulator, storing energy in the electric field between them. An inductor is the component that stores energy magnetically.

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Correct answer: a large static discharge between a charged cloud and the ground

Friction within storm clouds builds up a huge static charge, and when the resulting voltage is high enough to overcome the air's insulation, it discharges as a lightning strike.

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Correct answer: 5 ohms

Resistance equals voltage divided by current, so 25 / 5 = 5 ohms.

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Correct answer: 2 amperes

The total resistance is 3 + 7 = 10 ohms, and current equals voltage divided by resistance: 20 / 10 = 2 amperes.

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Correct answer: alternating current

A transformer works by a changing magnetic field inducing voltage in the second coil. Steady direct current produces no change, so nothing is induced and the transformer does nothing.

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