A direct current (DC) heating element is connected to a 120\text{ V} power supply. If an a… — Armed Services Vocational Aptitude Battery (ASVAB)

A direct current (DC) heating element is connected to a $120\text{ V}$ power supply. If an ammeter measures a current of $4\text{ A}$ flowing through the element, what is its electrical resistance?

A
$480\text{ }\Omega$
$30\text{ }\Omega$ Answer
C
$0.033\text{ }\Omega$
D
$116\text{ }\Omega$

Answer

30\text{ }\Omega

According to Ohm's law, electrical resistance (

R

) is defined as the ratio of voltage (

V

) across a component to the current (

I

) passing through it:

R = \frac{V}{I}

. Substituting

120\text{ V}

and

4\text{ A}

gives

R = \frac{120}{4} = 30\text{ }\Omega

Step-by-Step Solution

Identify the given values and the required quantity

Voltage

V = 120\text{ V}

, Current

I = 4\text{ A}

, Resistance

R

is unknown

Establishing the known circuit parameters determines which Ohm's law formula variation to use.

Apply Ohm's law rearranged to solve for resistance:

R = \frac{V}{I}

R = \frac{120\text{ V}}{4\text{ A}} = 30\text{ }\Omega

Resistance represents the opposition to current flow and is calculated as the ratio of electromotive force to electrical current.

Key Concept

Ohm's Law Resistance Calculation (

R = \frac{V}{I}

)

Estimated Time:45s

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

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