Electronics Information · Practice test 3

Correct answer: resistance

An ohmmeter reads resistance in ohms and should be used only on a circuit with the power off. A multimeter combines this function with those of the ammeter and voltmeter.

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Correct answer: each device gets full voltage and works independently

Parallel wiring gives every outlet the full supply voltage and keeps the devices independent, so switching off a lamp does not darken the room. Series wiring would fail on both counts.

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Correct answer: 6 ohms

Two equal resistors in parallel give half the value of one, so the total is 6 ohms.

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Correct answer: 720 watts

Power equals voltage times current, so 240 x 3 = 720 watts.

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Correct answer: 1 ohm

Adding the reciprocals: 1/2 + 1/3 + 1/6 = 3/6 + 2/6 + 1/6 = 1, so the total resistance is 1 ohm, lower than the smallest branch.

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Correct answer: 12 volts

Ohm's law states that voltage equals current times resistance, so 3 x 4 = 12 volts.

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Correct answer: gains or loses electrons

Rubbing transfers electrons from one surface to another, leaving one negatively charged and the other positively charged. Protons are locked in the nucleus and do not move, and grounding drains a static charge rather than creating one.

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Correct answer: 22,000 ohms

Red and red give the digits 2 and 2, and orange as the multiplier band means times 1000, so 22 x 1000 = 22,000 ohms.

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Correct answer: 1000 volts

The prefix kilo means one thousand, so a kilovolt is 1000 volts. Mega would mean a million and milli one thousandth.

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Correct answer: from the negative terminal toward the positive

Electrons are negative, so they are repelled by the negative terminal and drawn to the positive one. This is the opposite of conventional current, and both descriptions are in everyday use.

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Correct answer: a higher total voltage

In series the voltages add, so four 1.5 volt cells give 6 volts. Wiring them in parallel instead keeps the voltage at 1.5 but extends how long they last.

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Correct answer: the same current rating

The rating is chosen to protect the wiring, so fitting a larger fuse lets the wire overheat before the fuse ever blows. A repeatedly blowing fuse is a fault to trace, not a rating to raise.

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Correct answer: a switch operated by an electromagnet

A small current through the relay's coil creates a magnetic field that pulls contacts together, letting a weak signal switch a much larger load. That is how a car's starter circuit works.

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Correct answer: essentially zero

Ohm's law shows current equals voltage divided by resistance, so as resistance grows toward infinity, the current it allows shrinks toward zero, as in an open switch.

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Correct answer: double the value of one capacitor alone

Unlike resistors, capacitors in parallel add directly because the plate area effectively increases, so two equal capacitors in parallel give twice the capacitance of one.

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Correct answer: block nearly all current because of its very high internal resistance

A voltmeter is built with very high internal resistance so it draws almost no current when placed in parallel. Wired in series instead, that same high resistance would choke off nearly all the circuit's current.

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Correct answer: confirm it is dead with a meter or tester

A switch may be mislabelled, wired to the neutral, or fed from a second source, so the only safe assumption is the one you have measured. Testing by touch is never acceptable.

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Correct answer: 40 watts

With current and resistance known, power equals current squared times resistance: 2 squared is 4, and 4 x 10 = 40 watts. Multiplying current by resistance without squaring gives 20, which is actually the voltage across the resistor.

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Correct answer: lowers the skin's resistance, allowing more current to flow through the body

Water is a much better conductor than dry skin, so wet skin offers far less resistance. For the same voltage, that lets a larger and more dangerous current pass through the body.

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Correct answer: 480 volts

The secondary voltage follows the turns ratio: 120 x 240 / 60 = 480 volts, a step-up because the secondary has more turns than the primary.

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