ASVAB Electronics Information Practice Test 2: Ohm's Law, Power and Components
- Ohm's Law, Power and Components 2
- 10 questions
- 12 minutes
This test mixes calculations with Ohm's law (V = I × R) and the power formulas (P = V × I = I2 × R) with questions about what common components do. Convert milliamps and kilohms before calculating.
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Question 1
A 9-volt battery drives a current of 3 milliamperes through a resistor. What is the resistance?
Correct answer: A
R = V ÷ I = 9 ÷ 0.003 = 3,000 ohms, which is 3 kilohms. The answer 3 ohms forgets to convert milliamperes to amperes.
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Question 2
Resistors of 10 ohms, 20 ohms and 30 ohms are connected in series. What is the total resistance?
Correct answer: C
In series, resistances simply add: 10 + 20 + 30 = 60 ohms. About 5.5 ohms would be the total if they were connected in parallel.
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Question 3
A 1,200-watt hair dryer runs on a 120-volt outlet. How much current does it draw?
Correct answer: B
I = P ÷ V = 1,200 ÷ 120 = 10 amperes. Dividing the other way, 120 ÷ 1,200, gives 0.1, and multiplying gives 144,000.
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Question 4
Capacitance is measured in
Correct answer: D
The farad is the unit of capacitance. The henry measures inductance, the ohm resistance and the coulomb electric charge.
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Question 5
Which component stores energy in a magnetic field and opposes sudden changes in current?
Correct answer: D
An inductor is a coil of wire; its magnetic field resists changes in the current flowing through it. A capacitor stores energy in an electric field instead.
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Question 6
A resistor has the color bands brown, black, red (the fourth band shows tolerance). What is its resistance?
Correct answer: A
Brown = 1 and black = 0 give the digits 10, and red as the third band means multiply by 102 = 100, so 10 × 100 = 1,000 ohms. Reading red as the digit 2 gives the wrong answer 102.
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Question 7
What is the main purpose of a ground-fault circuit interrupter (GFCI) outlet?
Correct answer: B
A GFCI compares the current going out and coming back; if some leaks away, for example through a person, it shuts off the power in a fraction of a second. That is why GFCIs are used near water.
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Question 8
In electronic circuits, a transistor is most often used as
Correct answer: C
A small current or voltage at one terminal of a transistor controls a larger current, so it can switch a circuit on and off or amplify a signal.
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Question 9
A circuit that changes alternating current (AC) into direct current (DC) is called a
Correct answer: C
A rectifier uses diodes to let current flow in only one direction, turning AC into DC. An oscillator does roughly the reverse: it produces an alternating signal.
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Question 10
A current of 2 amperes flows through a 5-ohm resistor. How much power does the resistor use?
Correct answer: B
P = I2 × R = 22 × 5 = 20 watts. The answer 10 is I × R, which is the voltage across the resistor in volts, not the power.
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