ASVAB Electronics Information Practice Test: Circuits, Current, Voltage and Components
- Circuits, Current, Voltage and Components
- 15 questions
- 12 minutes
This test covers basic electricity: Ohm's law, electric power, series and parallel resistors, common components and household wiring. Tip: remember V = I × R and P = V × I; most calculation questions use one of these two formulas.
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Question 1
A 12-volt battery is connected to a 4-ohm resistor. How much current flows?
Correct answer: A
By Ohm's law, current = voltage ÷ resistance = 12 ÷ 4 = 3 A. 48 comes from multiplying instead of dividing.
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Question 2
A device draws 0.5 ampere from a 120-volt outlet. How much power does it use?
Correct answer: D
Power = voltage × current = 120 × 0.5 = 60 W. 240 comes from dividing 120 by 0.5.
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Question 3
The circuit has a 12-volt battery and two resistors in series.
What is the voltage across R2?
Correct answer: B
Total resistance is 2 + 4 = 6 Ω, so the current is 12 ÷ 6 = 2 A. The voltage across R2 is 2 × 4 = 8 V; the other 4 V drop across R1.
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Question 4
Two 6-ohm resistors are connected in parallel. What is their combined resistance?
Correct answer: C
Equal resistors in parallel give the value of one divided by the number of resistors: 6 ÷ 2 = 3 Ω. 12 Ω would be the series value.
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Question 5
A 12-ohm resistor and a 6-ohm resistor are connected in parallel. What is their combined resistance?
Correct answer: D
For two resistors in parallel, R = (12 × 6) ÷ (12 + 6) = 72 ÷ 18 = 4 Ω. The combined value is always smaller than the smallest resistor, so 9 Ω and 18 Ω cannot be right.
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Question 6
A 1,500-watt space heater runs for 4 hours. How much energy does it use?
Correct answer: A
1,500 W = 1.5 kW, and 1.5 kW × 4 h = 6 kWh. 6,000 is the answer in watt-hours, not kilowatt-hours.
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Question 7
Which of these materials is the best conductor of electricity?
Correct answer: B
Copper has many free electrons and very low resistance, which is why most wiring is made of it. Rubber, glass and dry wood are insulators.
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Question 8
What is the main job of a diode in a circuit?
Correct answer: C
A diode conducts in one direction and blocks the other, which is used to change AC into DC. Storing charge is the job of a capacitor, and changing AC voltage is the job of a transformer.
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Question 9
A capacitor is a component that
Correct answer: A
A capacitor has two conducting plates separated by an insulator and stores charge in the electric field between them. Its capacity is measured in farads.
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Question 10
What does a fuse do in a circuit?
Correct answer: D
A fuse contains a thin metal strip that melts when too much current flows, breaking the circuit and protecting the wiring from overheating. After it blows, it must be replaced.
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Question 11
Why are the outlets and lights in a house wired in parallel rather than in series?
Correct answer: B
In parallel, every branch is connected across the full supply voltage, and turning one device off does not break the path to the others. In a series circuit, one open switch or burned-out bulb stops current everywhere.
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Question 12
What is the frequency of standard household alternating current in the United States?
Correct answer: C
U.S. household power alternates 60 times per second (60 Hz) at about 120 volts. Many other countries, including most of Europe, use 50 Hz.
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Question 13
A transformer has 1,200 turns on its primary coil and 60 turns on its secondary coil. The primary is connected to 120 volts AC. What is the secondary voltage?
Correct answer: C
Voltage changes in the same ratio as the number of turns: 120 × 60 ÷ 1,200 = 6 V. Fewer turns on the secondary means a step-down transformer, so 2,400 V is the reversed ratio.
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Question 14
In standard U.S. household wiring, which wire color is used for the equipment ground?
Correct answer: A
The grounding conductor is green, green with a yellow stripe, or bare copper. Black and red are normally hot (live) wires, and white is the neutral.
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Question 15
Which copper wire has the lowest resistance?
Correct answer: B
Resistance increases with length and decreases as the wire gets thicker (larger cross-section). The shortest and thickest wire therefore has the least resistance.
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