Ohm's Law Practice Questions — Armed Services Vocational Aptitude Battery (ASVAB) — Page 2

Question 21Question →

A field technician is testing a direct-current (DC) sensor module. What is the current flowing through the circuit when a potential difference of $90\text{ V}$ is applied across a total circuit resistance of $15\text{ k}\Omega$ ?

Fill in the blanks below

Under an applied potential difference of

90\text{ V}

, a circuit having a resistance of

15\text{ k}\Omega

conducts a current of milliamperes.

Show answer & explanation

Answer

6 milliamperes (6 mA)

According to Ohm's law (

I = \frac{V}{R}

), dividing the

90\text{ V}

source by the

15,000\ \Omega

(

15\text{ k}\Omega

) total resistance yields

0.006\text{ A}

, which converts directly to

6\text{ mA}

.

Step-by-Step Solution

1

Identify known circuit quantities and convert resistance from kilohms to ohms.

V = 90\text{ V}

and

R = 15\text{ k}\Omega = 15 \times 1,000\ \Omega = 15,000\ \Omega

.

Standard electrical formulas require resistance in base units of ohms (

\Omega

) to calculate current in amperes (

\text{A}

).

2

Apply Ohm's law (

I = \frac{V}{R}

) to solve for the current in amperes.

I = \frac{90\text{ V}}{15,000\ \Omega} = 0.006\text{ A}

.

Current is directly proportional to voltage and inversely proportional to resistance.

3

Convert current from amperes to milliamperes as requested by the statement.

0.006\text{ A} \times 1,000\text{ mA/A} = 6\text{ mA}

.

One milliampere equals one thousandth of an ampere (

1\text{ mA} = 10^{-3}\text{ A}

).

Key Concept

Ohm's Law (

I = \frac{V}{R}

) defines the proportional relationship between potential difference, current, and resistance in a direct-current circuit.

Estimated Time:45s

Question 22Question →

An automotive diagnostic technician connects an auxiliary relay coil to a $12\text{ V}$ direct-current (DC) power supply. An ammeter placed in series measures a current of $150\text{ mA}$ . What is the electrical resistance of the relay coil?

1.8\ \Omega

12.5\ \Omega

80\ \Omega

800\ \Omega

Show answer & explanation

Answer: $80\ \Omega$

Answer

The electrical resistance of the relay coil is

80\ \Omega

.

According to Ohm's law, electrical resistance is calculated by dividing voltage by current (

R = \frac{V}{I}

). Converting

150\text{ mA}

to

0.15\text{ A}

and dividing

12\text{ V}

by

0.15\text{ A}

gives

80\ \Omega

.

Step-by-Step Solution

1

Convert the current from milliamperes (

\text{mA}

) to base units of amperes (

\text{A}

).

I = 150\text{ mA} = 150 \times 10^{-3}\text{ A} = 0.15\text{ A}

Ohm's law requires values in standard SI base units (volts, amperes, and ohms) before performing calculations.

2

Rearrange Ohm's law (

V = I \times R

) to solve for resistance (

R

) and substitute the given values.

R = \frac{V}{I} = \frac{12\text{ V}}{0.15\text{ A}} = 80\ \Omega

Resistance is equal to the potential difference divided by the current flowing through the component.

Key Concept

Ohm's Law states that resistance equals voltage divided by current (

R = \frac{V}{I}

), requiring current to be expressed in amperes.

Estimated Time:45s

Question 23Question →

A shipboard auxiliary alarm horn is connected across a $72\text{ V}$ direct-current (DC) power rail. When activated, the horn draws a steady current of $120\text{ mA}$ . Based on Ohm's Law, what is the total electrical resistance of the horn circuit in ohms ( $\Omega$ )?

Show answer & explanation

Answer: 600

Answer

The total electrical resistance of the horn circuit is

600\ \Omega

.

According to Ohm's Law, resistance equals voltage divided by current (

R = \frac{V}{I}

). Converting

120\text{ mA}

to standard amperes gives

0.12\text{ A}

. Dividing

72\text{ V}

by

0.12\text{ A}

yields an electrical resistance of

600\ \Omega

.

Step-by-Step Solution

1

Convert the current measurement from milliamperes to base amperes.

I = 120\text{ mA} = 0.12\text{ A}

Ohm's Law requires standard SI units (volts, amperes, and ohms) for direct substitution.

2

Rearrange Ohm's Law (

V = I \times R

) to isolate resistance (

R

).

R = \frac{V}{I}

The unknown quantity in this circuit problem is resistance.

3

Divide the applied voltage by the circuit current.

R = \frac{72\text{ V}}{0.12\text{ A}} = 600\ \Omega

Evaluating the division yields the equivalent circuit resistance in ohms.

Key Concept

Ohm's Law defines the proportional relationship between voltage, current, and resistance (

R = \frac{V}{I}

).

Estimated Time:45s

Question 24Question →

A technician is testing a telemetry circuit board and measures a steady direct current of $40\text{ mA}$ flowing through a $750\ \Omega$ load resistor. What is the voltage drop across this resistor?

300\text{ V}

18.75\text{ V}

30\text{ V}

3.0\text{ V}

Show answer & explanation

Answer: $30\text{ V}$

Answer

30\text{ V}

According to Ohm's Law (

V = I \times R

), the voltage drop across a component is calculated by multiplying the current flowing through it by its resistance. Converting

40\text{ mA}

to standard amperes gives

0.040\text{ A}

. Multiplying

0.040\text{ A}

by

750\ \Omega

yields a potential difference of

30\text{ V}

.

Step-by-Step Solution

1

Convert current from milliamperes (mA) to base amperes (A)

I = 40\text{ mA} = 40 \times 10^{-3}\text{ A} = 0.040\text{ A}

Standard electrical calculations using Ohm's Law require base units of amperes, ohms, and volts.

2

Apply Ohm's Law to determine the potential difference (

V = I \times R

)

V = 0.040\text{ A} \times 750\ \Omega = 30\text{ V}

Voltage drop across a resistive element is directly proportional to the product of the current and resistance.

Key Concept

Ohm's Law (

V = I \times R

) and metric unit conversion

Estimated Time:45s

Question 25Question →

An aircraft instrument panel contains a direct-current (DC) indicator circuit powered by a $120\text{ V}$ source. What are the resulting circuit currents under each resistance condition? Fill in the blanks with the correct numerical values.

Fill in the blanks below

When connected to a

2.4\text{ k}\Omega

resistor, the current is

\text{mA}

. If the resistance is increased to

4.8\text{ k}\Omega

while maintaining constant voltage, the new current is

\text{mA}

.

Show answer & explanation

Answer

The current with a

2.4\text{ k}\Omega

resistor is

50\text{ mA}

, and the current with a

4.8\text{ k}\Omega

resistor is

25\text{ mA}

.

According to Ohm's Law (

I = \frac{V}{R}

), converting

2.4\text{ k}\Omega

to

2400\ \Omega

yields an initial current of

\frac{120\text{ V}}{2400\ \Omega} = 0.05\text{ A} = 50\text{ mA}

. When the resistance doubles to

4.8\text{ k}\Omega

(

4800\ \Omega

) with constant voltage, the current is halved to

25\text{ mA}

.

Step-by-Step Solution

1

Convert the first resistance value from kilohms to ohms and apply Ohm's Law to calculate the initial current

R_1 = 2.4\text{ k}\Omega = 2400\ \Omega

;

I_1 = \frac{V}{R_1} = \frac{120\text{ V}}{2400\ \Omega} = 0.05\text{ A} = 50\text{ mA}

Ohm's Law states that current equals voltage divided by resistance (

I = \frac{V}{R}

).

2

Convert the second resistance value or apply the principle of inverse proportionality to find the new current

R_2 = 4.8\text{ k}\Omega = 4800\ \Omega

;

I_2 = \frac{120\text{ V}}{4800\ \Omega} = 0.025\text{ A} = 25\text{ mA}

(or since resistance doubled at constant voltage, current halved:

\frac{50\text{ mA}}{2} = 25\text{ mA}

)

Current is inversely proportional to resistance when voltage remains constant.

Key Concept

Ohm's Law (

I = \frac{V}{R}

) and inverse proportionality between current and resistance at constant voltage

Estimated Time:45s

Question 26Question →

A radar transceiver module operates on a $45\text{ V}$ direct-current (DC) power line. When the module is active, a series ammeter registers a current of $15\text{ mA}$ . What is the total electrical resistance of the module?

3\ \Omega

3\text{ k}\Omega

675\ \Omega

333\ \Omega

Show answer & explanation

Answer: $3\text{ k}\Omega$

Answer

3\text{ k}\Omega

(or

3,000\ \Omega

)

According to Ohm's Law, resistance is the quotient of voltage divided by current (

R = \frac{V}{I}

). Converting

15\text{ mA}

to standard units gives

0.015\text{ A}

. Dividing the

45\text{ V}

potential difference by

0.015\text{ A}

results in

3,000\ \Omega

, which is equivalent to

3\text{ k}\Omega

.

Step-by-Step Solution

1

Convert the current measurement from milliamperes to base amperes.

I = 15\text{ mA} = 15 \times 10^{-3}\text{ A} = 0.015\text{ A}

Ohm's Law calculations require current to be expressed in standard SI units (amperes) to yield resistance in ohms.

2

Rearrange Ohm's Law (

V = I \times R

) to solve for resistance (

R

).

R = \frac{V}{I}

Isolating the unknown variable allows direct substitution of known circuit values.

3

Substitute the voltage and current values into the rearranged formula.

R = \frac{45\text{ V}}{0.015\text{ A}} = 3,000\ \Omega = 3\text{ k}\Omega

Dividing the potential difference by the current yields the total circuit resistance.

Key Concept

Ohm's Law defines the fundamental linear relationship between voltage, current, and resistance (

V = I \times R

).

Estimated Time:45s

Question 27Question →

An avionics technician is troubleshooting a direct-current (DC) audio preamplifier circuit. The circuit is powered by an $18\text{ V}$ DC source and draws a steady current of $2.5\text{ mA}$ . What is the total resistance of the circuit in kilohms ( $\text{k}\Omega$ )?

Show answer & explanation

Answer: 7.2

Answer

7.2 kΩ

According to Ohm's Law, resistance is determined by dividing voltage by current (

R = \frac{V}{I}

). Converting

2.5\text{ mA}

to

0.0025\text{ A}

and dividing

18\text{ V}

by

0.0025\text{ A}

yields

7200\ \Omega

, which equals

7.2\text{ k}\Omega

.

Step-by-Step Solution

1

Convert the current measurement from milliamperes (mA) to base amperes (A)

I = 2.5\text{ mA} = 0.0025\text{ A}

Ohm's Law formulas require electrical quantities to be in standard base units (volts, amperes, and ohms) before computation.

2

Apply Ohm's Law rearranged to solve for resistance (

R = \frac{V}{I}

)

R = \frac{18\text{ V}}{0.0025\text{ A}} = 7200\ \Omega

Resistance equals the electromotive force divided by the resulting current flow.

3

Convert the calculated resistance from ohms (Ω) to kilohms (kΩ)

R = \frac{7200\ \Omega}{1000\ \Omega/\text{k}\Omega} = 7.2\text{ k}\Omega

The question specifically requests the final numerical value in kilohms.

Key Concept

Ohm's Law (

R = \frac{V}{I}

) with metric prefix conversion (

1\text{ mA} = 10^{-3}\text{ A}

and

1\text{ k}\Omega = 10^{3}\ \Omega

)

Estimated Time:45s

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