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Electrical practice questions

30 questions from the ase automotive fundamentals practice test.

Electrical practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

Two 6-ohm resistors are connected in series across a 12-volt battery. How much current flows?

  1. 2 amps
  2. 4 amps
  3. 1 amp
  4. 72 amps
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C. 1 amp

Series resistances add: 6 + 6 = 12 ohms, and 12 V / 12 ohms = 1 A. The answer 4 A comes from treating the resistors as if they were in parallel (3 ohms).

Reference: Ohm's law; series circuits

How much current does a 60-watt bulb draw on a 12-volt circuit?

  1. 5 amps
  2. 0.2 amp
  3. 72 amps
  4. 720 amps
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A. 5 amps

Power equals volts times amps, so amps = watts / volts = 60 / 12 = 5 A. Dividing the wrong way round gives 0.2, and multiplying gives 720.

Reference: Watt's law (P = E x I)

With the engine at about 2,000 rpm and the accessories off, which voltage at the battery shows normal charging?

  1. 12.4 volts
  2. 14.2 volts
  3. 11.8 volts
  4. 16.1 volts
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B. 14.2 volts

A working charging system holds the battery roughly in the mid-13 to mid-14 volt range. A reading near 12.4 volts or lower means the alternator is not charging, and about 16 volts is overcharging that can damage the battery and electronics.

Reference: Charging system voltage test

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