Electronics Information · Practice test 5

Correct answer: 50 hertz

Frequency is simply the number of cycles per second, so 50 cycles each second is a frequency of 50 hertz.

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Correct answer: hertz

Hertz counts cycles per second, so 60 hertz means the current reverses direction sixty times each second. Farads measure capacitance and henries measure inductance.

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Correct answer: how much charge passes a given point each second

Current is a rate of charge flow, one ampere being one coulomb of charge passing a point every second. Voltage, not current, describes the driving pressure.

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Correct answer: any change in the current through it

A changing current in a coil induces a voltage that fights the change, so an inductor resists current rising or falling quickly. A capacitor is the mirror image: it opposes changes in voltage.

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Correct answer: 2 amperes

Rearranging Ohm's law, current equals voltage divided by resistance, so 12 / 6 = 2 amperes. Dividing the other way round gives 0.5, the usual slip.

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Correct answer: raise the voltage delivered to the secondary circuit

More turns on the secondary than the primary raises the secondary voltage in proportion to the turns ratio, which is what makes a transformer a step-up type.

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Correct answer: stop carrying any current at all

A series circuit has only one path for current, so a single open anywhere along it interrupts the entire loop and every component stops receiving current.

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Correct answer: can have its chemical reaction reversed by charging

A secondary cell is rechargeable: passing current back through it reverses the reaction and restores the charge. A primary cell, such as an ordinary alkaline battery, cannot be recharged safely.

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Correct answer: an integrated circuit containing thousands or millions of components

A microcontroller packs a processor, memory, and supporting circuitry onto one chip, all built using integrated circuit fabrication, which is why such complex control can fit in a small package.

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Correct answer: Copper

Copper's loosely held outer electrons move freely, which makes it an excellent conductor and the standard choice for wiring. The other three are insulators.

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Correct answer: 12 ohms

Series resistances add directly, so 4 + 8 = 12 ohms. The choice 2.67 is what the pair would give in parallel.

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Correct answer: 54 watts

Power equals current squared times resistance: 3 squared is 9, and 9 x 6 = 54 watts. Multiplying current by resistance without squaring gives 18, which is the voltage drop, not the power.

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Correct answer: detecting current leaking to ground and cutting power

A ground fault interrupter compares the current going out with the current coming back, and if even a small amount is escaping, possibly through a person, it cuts the supply in milliseconds. That is why they are required near water.

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Correct answer: 470 ohms

Yellow and violet give the digits 4 and 7, and brown as the multiplier band means times 10, so 47 x 10 = 470 ohms.

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Correct answer: a safe path for fault current to flow away

Ground gives stray current a low-resistance route to earth rather than through a person touching the equipment, and it also serves as the zero reference for measuring voltage.

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Correct answer: flows in one direction only

Direct current keeps a steady direction, which is what batteries and most electronic circuits supply. Alternating current is the one that reverses.

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Correct answer: a switch or an amplifier

A small current or voltage at one terminal controls a much larger one between the other two, which lets a transistor either amplify a signal or switch a load on and off.

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Correct answer: a low-power signal control a much higher-power load safely

The small coil current needed to operate a relay's contacts is electrically isolated from the larger load current those contacts switch, protecting the control circuit and its operator.

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Correct answer: rises, falls, reverses, and returns to its starting value

One AC cycle covers a full swing from zero to a positive peak, back through zero to a negative peak, and back to zero again. That pattern repeats at the supply frequency.

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Correct answer: henries

The henry measures inductance, the farad measures capacitance, and the hertz measures frequency. Keeping the three straight is worth a few marks on the test.

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