Electronics Information · Practice test 8

20 questions · 9 minutes

Answer every question, then tap Check results to see your score and the method behind each answer.

Question 1Not answered

Resistance in a circuit
1. opposes the flow of current
2. increases the flow of current
3. stores charge for later use
4. reverses the direction of flow
Correct answer: opposes the flow of current

Resistance holds back current and converts some electrical energy into heat, which is how a heating element or a filament works. Storing charge is what a capacitor does.

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Question 2Not answered

Three 30 ohm resistors are connected in parallel. What is the total resistance?
1. 90 ohms
2. 30 ohms
3. 10 ohms
4. 15 ohms
Correct answer: 10 ohms

For equal resistors in parallel, divide one value by how many there are: 30 / 3 = 10 ohms. The choice 90 is the series total.

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Question 3Not answered

A resistor is banded brown, black, red. What is its resistance?
1. 100 ohms
2. 1,000 ohms
3. 102 ohms
4. 10,000 ohms
Correct answer: 1,000 ohms

Brown is 1 and black is 0, giving the digits 10. Red as the third band means multiply by 100, so 10 x 100 = 1,000 ohms. Reading the third band as a digit rather than a multiplier gives 102.

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Question 4Not answered

A transformer has 400 turns on its primary and 100 turns on its secondary. With 100 volts applied to the primary, what is the secondary voltage?
1. 400 volts
2. 100 volts
3. 10 volts
4. 25 volts
Correct answer: 25 volts

The secondary voltage follows the turns ratio: 100 x 100 / 400 = 25 volts, a step-down transformer because it has fewer secondary turns.

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Question 5Not answered

A 15 ohm heater draws 2 amperes. What voltage is across it?
1. 7.5 volts
2. 17 volts
3. 13 volts
4. 30 volts
Correct answer: 30 volts

Voltage equals current times resistance, so 2 x 15 = 30 volts.

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Question 6Not answered

One megohm is equal to
1. 1000 ohms
2. 0.000001 ohms
3. 1,000,000 ohms
4. 100 ohms
Correct answer: 1,000,000 ohms

Mega means one million, so a megohm is 1,000,000 ohms, a value common in high-resistance components such as some potentiometers.

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Question 7Not answered

Two charged objects with charges of the same sign, when brought near each other, will
1. attract one another
2. have no force between them
3. immediately discharge to neutral
4. repel one another
Correct answer: repel one another

Like charges repel and unlike charges attract. This basic rule explains why a charged balloon pushes away another charged balloon of the same sign.

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Question 8Not answered

The defining feature of alternating current is that it
1. flows steadily in one direction
2. carries a higher voltage than direct current
3. can travel only through a vacuum
4. reverses direction at regular intervals
Correct answer: reverses direction at regular intervals

Alternating current periodically switches direction, sixty times a second on standard household supply. Direct current, as from a battery, flows one way only. Neither is inherently higher in voltage.

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Question 9Not answered

A photodiode is a semiconductor device that
1. produces light when current flows through it
2. amplifies a current using a base signal
3. produces a current in response to light striking it
4. blocks current in both directions permanently
Correct answer: produces a current in response to light striking it

A photodiode works opposite to an LED: instead of turning current into light, it generates a small current when light falls on its junction, which makes it useful as a light sensor.

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Question 10Not answered

A single-pole, single-throw switch
1. opens or closes one circuit
2. switches one circuit between two paths
3. controls two circuits at once
4. varies the current continuously
Correct answer: opens or closes one circuit

Pole counts the circuits controlled and throw counts the positions available, so single-pole single-throw is a plain on-off switch. A single-pole double-throw would send one circuit down either of two paths.

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Question 11Not answered

An LED must always be installed with attention to its polarity because it
1. will explode if reversed
2. produces a different color when reversed
3. only works on alternating current
4. conducts, and lights, in only one direction
Correct answer: conducts, and lights, in only one direction

As a diode, an LED only conducts when forward biased. Installed backward, it simply stays dark and blocks the current rather than lighting up.

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Question 12Not answered

Electrical wires are insulated chiefly to
1. stop conductors from touching each other or a person
2. increase the current the wire can carry
3. lower the resistance of the conductor
4. keep the copper from cooling too quickly
Correct answer: stop conductors from touching each other or a person

Insulation confines the current to its intended path, preventing shorts between conductors and shocks to anyone handling the wire. It does not change the conductor's own resistance.

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Question 13Not answered

If the voltage applied to a fixed resistor is tripled, the current through it will
1. become three times smaller
2. stay exactly the same
3. become nine times as large
4. become three times as large
Correct answer: become three times as large

With resistance fixed, current is directly proportional to voltage, so tripling the voltage triples the current. Only power, which depends on voltage squared, would rise ninefold.

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Question 14Not answered

Compared with an incandescent bulb of similar brightness, an LED typically
1. uses more power and burns out sooner
2. uses less power and lasts far longer
3. requires alternating current to operate at all
4. produces light by heating a metal filament
Correct answer: uses less power and lasts far longer

An LED converts most of its electrical energy directly into light rather than heat, and it has no filament to burn out, so it uses less power and lasts much longer than an incandescent bulb.

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Question 15Not answered

A dead short develops directly across the terminals of a battery. The current drawn from the battery will
1. drop to zero immediately
2. rise sharply, limited mainly by the battery's own internal resistance
3. stay the same as under normal load
4. reverse direction through the battery
Correct answer: rise sharply, limited mainly by the battery's own internal resistance

With almost no external resistance, current is limited chiefly by the battery's small internal resistance, so it can become very large, heating the battery and its wiring rapidly.

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Question 16Not answered

Compared with 12 gauge wire, 22 gauge wire is
1. thicker and has a higher safe current rating
2. thinner and has a lower safe current rating
3. the same thickness but made of a different metal
4. thinner but rated to carry more current
Correct answer: thinner and has a lower safe current rating

Wire gauge numbers run opposite to thickness, so 22 gauge is thinner than 12 gauge, has more resistance per foot, and is rated for less current.

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Question 17Not answered

A transformer has 100 turns on the primary and 50 on the secondary. With 240 volts applied to the primary, what is the secondary voltage?
1. 480 volts
2. 240 volts
3. 60 volts
4. 120 volts
Correct answer: 120 volts

Output voltage follows the turns ratio, so halving the turns halves the voltage: 240 x 50 / 100 = 120 volts. Inverting the ratio gives 480, which would be a step-up transformer.

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Question 18Not answered

An integrated circuit is typically manufactured on a thin wafer of
1. silicon
2. copper
3. rubber
4. glass
Correct answer: silicon

Silicon's semiconductor properties, and the ease of doping it precisely, make it the standard base material for building the transistors and connections inside an integrated circuit.

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Question 19Not answered

What resistance allows 4 amperes to flow when 24 volts is applied?
1. 96 ohms
2. 28 ohms
3. 6 ohms
4. 0.17 ohms
Correct answer: 6 ohms

Resistance equals voltage divided by current, so 24 / 4 = 6 ohms.

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Question 20Not answered

A fuse rated for 15 amperes is intended to
1. limit the circuit's voltage to 15 volts
2. open the circuit once current exceeds about 15 amperes
3. allow unlimited current as long as it is brief
4. regulate the circuit's current to exactly 15 amperes at all times
Correct answer: open the circuit once current exceeds about 15 amperes

A fuse's rating states the current at which its element melts and opens the circuit, protecting the wiring from overheating. It does nothing to regulate voltage.

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