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ASVAB Physics — practice by topic

Browse 14 questions across 1 Physics topics. Choose what you want to revise, then open a question to check its answer and worked solution.

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Physics topics

Electric Current, Resistance, and Ohm's Law (14)

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A 3.00-V flashlight bulb has a hot resistance of 3.60 ohms. What current flows through it?Read the answer and worked solution →A flashlight passes a total of 600 C of charge in 0.500 h. What is the average current?Read the answer and worked solution →A car's starter motor draws 150 A while the battery holds 11.0 V across it. What is the motor's effective resistance?Read the answer and worked solution →An indicator light on a DVD player has a resistance of 140 ohms and passes 25.0 mA. What voltage supplies it?Read the answer and worked solution →

Worked practice questions

A 3.00-V flashlight bulb has a hot resistance of 3.60 ohms. What current flows through it?

  1. 0.83 A
  2. 1.20 A
  3. 10.8 A
  4. 0.12 A
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Correct answer: A. 0.83 A

1. Ohm's law gives current as I = V/R. 2. Substitute: I = 3.00 V / 3.60 ohms. 3. Divide: I = 0.83 A. 4. 10.8 A is the trap of multiplying voltage by resistance instead of dividing. _Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section 20.2 Ohm's Law: Resistance and Simple Circuits_

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A flashlight passes a total of 600 C of charge in 0.500 h. What is the average current?

  1. 0.15 A
  2. 0.33 A
  3. 1.20 A
  4. 3.30 A
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Correct answer: B. 0.33 A

1. Current is the rate of charge flow: I = charge / time, with time in seconds. 2. Convert the time: 0.500 h = 1,800 s. 3. Divide: I = 600 C / 1,800 s = 0.33 A. 4. 0.15 A comes from dividing by 3,600 s as if the charge had taken a full hour. _Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section 20.1 Current_

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A car's starter motor draws 150 A while the battery holds 11.0 V across it. What is the motor's effective resistance?

  1. 0.73 ohm
  2. 13.6 ohm
  3. 0.073 ohm
  4. 1.36 ohm
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Correct answer: C. 0.073 ohm

1. Rearranging Ohm's law I = V/R gives R = V/I. 2. Substitute: R = 11.0 V / 150 A. 3. Divide: R = 0.073 ohm. 4. A starter has to pass a very large current from a small voltage, so its resistance must be tiny. 5. 13.6 ohm is the trap of dividing current by voltage upside down and misplacing the decimal; it would allow less than one ampere to flow. _Source: OpenStax College Physics (CC BY 4.0), Ch 20 "Electric Current, Resistance, and Ohm's Law", section 20.2 Ohm's Law: Resistance and Simple Circuits_

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