Ohm’s Law for Technician License Exam

The questions covered in this article are from the NCVEC Technician (2014 – 2018) license exam question pool.

Ohm’s law states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them.  The law was named after the German physicist Georg Ohm.

I = \frac{V}{R}   where I = current; V = voltage; R = resistance

Ohm’s Law WHEEL

The hub of the Ohm’s Law Wheel depicts the values to be computed using Ohm’s Law.  The spokes of the Wheel show the expressions that can be used to compute the desired values.

An Ohm’s law calculator is available at the link below.

Ohm’s Law Calculator

Although the Ohm’s Law Wheel is a useful tool to have, you don’t have to memorize the various combinations associated with it to pass your license exam.

You will need to memorize two equations.

E = IR and P = IE

where E= voltage (volts); I = current (amperes); R=resistance (ohms); P = power (watts)

By combining and/or rearranging  the two equations, you can easily answer all the exam questions pertaining to Ohm’s law you will encounter on your Technician license exam.

Technician Exam Ohm’s Law Questions

T5D04 (B) | What is the resistance of a circuit in which a current of 3 amperes flows through a resistor connected to 90 volts?

A. 3 ohms
B. 30 ohms
C. 93 ohms
D. 270 ohms

remember: E = IR

rearrange the equation to get R = E / I and insert the values given in the question into the equation.

R = 90 volts / 3 amperes

R = 30 ohms which is answer B to the question

T5D05 (C) | What is the resistance in a circuit for which the applied voltage is 12 volts and the current flow is 1.5 amperes?

A. 18 ohms
B. 0.125 ohms
C. 8 ohms
D. 13.5 ohms

remember: E = IR

rearrange the equation to get  R = E / I and insert the values given in the question into the equation.

R = 12 volts / 1.5 amperes

R = 8 ohms which is answer C to the question

T5D06 (A) | What is the resistance of a circuit that draws 4 amperes from a 12-volt source?

A. 3 ohms
B. 16 ohms
C. 48 ohms
D. 8 Ohms

remember: E = IR

rearrange the equation to get R = E / I and insert the values given in the question into the equation.

R = 12 volts / 4 amperes

R = 3 ohms which is answer A to the question

T5D07 (D) | What is the current flow in a circuit with an applied voltage of 120 volts and a resistance of 80 ohms?

A. 9600 amperes
B. 200 amperes
C. 0.667 amperes
D. 1.5 amperes

remember: E = IR

rearrange the equation to get I = E / R and insert the values given in the question into the equation.

I = 120 volts / 80 ohms

I = 1.5 amperes which is answer D to the question

T5D08 (C) | What is the current flowing through a 100-ohm resistor connected across 200 volts?

A. 20,000 amperes
B. 0.5 amperes
C. 2 amperes
D. 100 amperes

remember: E = IR

rearrange the equation to get  I = E / R and insert the values given in the question into the equation.

I = 200 volts / 100 ohms

I = 2 amperes which is answer C to the question

T5D09 (C) | What is the current flowing through a 24-ohm resistor connected across 240 volts?

A. 24,000 amperes
B. 0.1 amperes
C. 10 amperes
D. 216 amperes

remember: E = IR

rearrange the equation to get  I = E / R and insert the values given in the question into the equation.

I = 240 volts / 24 ohms

I = 10 amperes which is answer C to the question

T5D10 (A) | What is the voltage across a 2-ohm resistor if a current of 0.5 amperes flows through it?

A. 1 volt
B. 0.25 volts
C. 2.5 volts
D. 1.5 volts

remember: E = IR

insert the values given in the question into the question into the equation.

E = .5 amperes X 2 ohms

E = 1 volt which is answer A to the question

T5D11 (B) | What is the voltage across a 10-ohm resistor if a current of 1 ampere flows through it?

A. 1 volt
B. 10 volts
C. 11 volts
D. 9 volts

remember: E = IR

insert the values given in the question into the equation.

E = 1 ampere X 10 ohms

E = 10 volts which is answer B to the question

T5D12 (D) | What is the voltage across a 10-ohm resistor if a current of 2 amperes flows through it?

A. 8 volts
B. 0.2 volts
C. 12 volts
D. 20 volts

remember: E = IR

insert the values given in the question into the equation.

E = 2 amperes X 10 ohms

E = 20 volts which is answer D to the question

T5C08 (A) | What is the formula used to calculate electrical power in a DC circuit?

A. Power (P) equals voltage (E) multiplied by current (I)
B. Power (P) equals voltage (E) divided by current (I)
C. Power (P) equals voltage (E) minus current (I)
D. Power (P) equals voltage (E) plus current (I)

remember: P = IE which is answer A to the question.

T5C09 (A) | How much power is being used in a circuit when the applied voltage is 13.8 volts DC and the current is 10 amperes?

A. 138 watts
B. 0.7 watts
C. 23.8 watts
D. 3.8 watts

remember: P = IE

insert the values given in the question into the equation.

P = 10 amperes X 13.8 volts

P = 138 watts which is answer A to the question.

T5C10 (B) | How much power is being used in a circuit when the applied voltage is 12 volts DC and the current is 2.5 amperes?

A. 4.8 watts
B. 30 watts
C. 14.5 watts
D. 0.208 watts

remember: P = IE

insert the values given in the question into the equation.

P = 2.5 amperes X 12 volts

P = 30 watts which is answer B to the question.

T5C11 (B) How many amperes are flowing in a circuit when the applied voltage is 12 volts DC and the load is 120 watts?

A. 0.1 amperes
B. 10 amperes
C. 12 amperes
D. 132 amperes

remember: P = IE

rearrange the equation to get I = P/E and insert the values given in the question into the equation.

I = 120 watts / 12 volts

I = 10 amperes

I = 10 amperes which is answer B to the question.

 

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