Electrical Theory & Principles — NASCLA Electrical Practice Questions

11 questions · 11% of the NASCLA Electrical exam

Worked questions

1. The control schematic shows the source voltage and total loop resistance. What current should the ammeter indicate?

2 amperes
B0.5 ampere
C12 amperes
D288 amperes

Why A is correct

Ohm's law gives I = V/R = 24/12 = 2 amperes; multiplying voltage by resistance produces the wrong quantity. The best answer is therefore “2 amperes.” The other choices either address a different system, rely on an unsafe shortcut, or make a conclusion not supported by the stated facts.

2. On a single-family remodel during plan review, a single-phase resistive load draws 10 amperes at 240 volts; what is its power?

A24 watts
B240 watts
C24,000 watts
2,400 watts

Why D is correct

For a resistive single-phase load, P = V × I = 240 × 10 = 2,400 watts. The best answer is therefore “2,400 watts.” The other choices either address a different system, rely on an unsafe shortcut, or make a conclusion not supported by the stated facts.

3. The diagram shows two equal resistors connected in parallel. What is the equivalent resistance at the terminals?

A400 ohms
B20 ohms
10 ohms
D40 ohms

Why C is correct

Two equal resistances in parallel produce half the resistance of either branch, so the equivalent is 10 ohms. The best answer is therefore “10 ohms.” The other choices either address a different system, rely on an unsafe shortcut, or make a conclusion not supported by the stated facts.

4. Using the transformer data shown, what secondary voltage is expected for an ideal transformer?

A480 volts
120 volts
C4 volts
D1,920 volts

Why B is correct

Ideal transformer voltage follows turns ratio, so 480 divided by 4 is 120 volts. The best answer is therefore “120 volts.” The other choices either address a different system, rely on an unsafe shortcut, or make a conclusion not supported by the stated facts.

5. Three resistors of 4, 6, and 10 ohms are connected in series. What is total resistance?

A10 ohms
B240 ohms
20 ohms
D2.4 ohms

Why C is correct

Series resistances add directly because the same current passes through each element. Four plus six plus ten equals twenty ohms; reciprocal addition is used for parallel branches.

6. An ideal transformer steps voltage down by a factor of four. What happens to secondary current for the same apparent power?

Four times the current
BIt becomes one-fourth
CIt remains identical
DIt becomes zero

Why A is correct

An ideal transformer approximately conserves volt-amperes, so current changes inversely with voltage. Reducing voltage to one-fourth raises available current by a factor of four.

5 more in the bank

Answers and explanations for these are in the app.

On a school modernization during plan review, which additional factor appears in the balanced three-phase real-power equation compared with the basic single-phase equation?
On a warehouse conversion during plan review, an inductive load has the same real power after power-factor correction; what generally happens to line current?
On a multifamily project during plan review, why does a transformer require changing magnetic flux for normal operation?
On a retail shell project during plan review, with load current and conductor material unchanged, what happens to voltage drop when circuit length doubles?
A 2-kilowatt heater runs for 3 hours. How much energy does it use?

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