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BASIC NEC 2023

Electrical Power & Energy Basics Practice Test

Free online electrical power and energy practice test. 25 basic electrical questions on watts vs kilowatt-hours, the power formula, power factor, and calculating electricity costs. Good for electrician exam prep.

TOPICS COVERED

Power Formula Power Calculation Power Formula Variations Power vs Energy Energy Units kWh Calculation

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Every electrician needs to know the difference between power and energy. Power (measured in watts) is the instantaneous rate at which electricity is used, while energy (measured in watt-hours or kilowatt-hours) is power used over time — it is what shows up on a utility bill. The basic power formula, P = V × I, connects voltage, current, and power, and it can be rearranged into P = I²R or P = V²/R depending on what you know. You will also need to understand the power triangle — real power (kW), reactive power (kVAR), and apparent power (kVA) — and how power factor compares the power actually doing useful work to the total power the utility must supply.

25

Questions

38 min

Time

75%

Pass

Timer starts immediately. Progress is auto-saved.

Electrical Power & Energy Basics Practice Test — Question List

Question 1: The basic formula for electrical power in a DC circuit is:

P = V x I
P = V / I
P = V + I
P = I / V

Question 2: A circuit operates at 120 V and draws 5 A. How much power is it using?

24 W
125 W
600 W
6000 W

Question 3: Which power formula should you use if you know only the current and the resistance?

P = V x I
P = I<sup>2</sup>R
P = V<sup>2</sup>/R
P = V/R

Question 4: A heating element has 10 ohms of resistance and carries 4 amps. How much power does it dissipate?

40 W
140 W
160 W
400 W

Question 5: A 240 V heater has a resistance of 24 ohms. Using P = V²/R, how much power does it use?

10 W
240 W
2400 W
5760 W

Question 6: What is the key difference between power and energy?

Power is an instantaneous rate; energy is power used over a period of time
They mean exactly the same thing
Energy is measured only in amps
Power is measured only in volts

Question 7: Electrical energy delivered to a home is billed by the utility company in which unit?

Watts (W)
Kilowatt-hours (kWh)
Volts (V)
Ohms (Ω)

Question 8: A 1500 W heater runs for 4 hours. How many kWh of energy did it consume?

1.5 kWh
4 kWh
6 kWh
60 kWh

Question 9: A 100 W light bulb is left on for 10 hours. How many kWh does it use?

0.1 kWh
1 kWh
10 kWh
100 kWh

Question 10: Electricity costs $0.15 per kWh. If an appliance uses 6 kWh, what does it cost to run?

$0.09
$0.90
$9.00
$1.50

Question 11: A 2000 W space heater runs for 3 hours. If electricity costs $0.12 per kWh, what is the total cost?

$0.24
$0.72
$2.40
$7.20

Question 12: On a utility bill, "demand" (measured in kW) is different from "consumption" (measured in kWh) because demand measures:

The highest rate of power draw over a short period, not the total energy used
The exact same thing as total energy consumed
The total number of hours the power was on
The voltage level supplied to the building

Question 13: In the power triangle, "real power" (measured in watts or kW) represents:

The power that actually does useful work, such as producing heat, light, or motion
Power that is stored and returned by inductors and capacitors without doing work
The total power a utility must be capable of supplying
Power lost only in transformer cores

Question 14: Reactive power, measured in VAR or kVAR, is best described as power that:

Is stored and released by inductors and capacitors but does no real work
Is always larger than the real power in any circuit
Is the power billed on the customer's monthly bill
Only exists in DC circuits

Question 15: Apparent power, measured in VA or kVA, represents:

Only the power consumed by resistive loads
The total combination of real and reactive power that the source must supply
Power that only exists in three-phase systems
The power lost as heat in conductors only

Question 16: Between real power and apparent power, which one actually performs useful work in a circuit?

Only real power
Only apparent power
Both do exactly equal amounts of work
Neither one does any work

Question 17: Power factor (PF) is defined as:

PF = kW / kVA
PF = kVA / kW
PF = kW x kVA
PF = kVAR / kW

Question 18: A motor draws 8 kVA of apparent power and delivers 6.4 kW of real power. What is its power factor?

0.6
0.8
1.25
8.0

Question 19: A power factor of 1.0 (unity power factor) means:

Real power equals apparent power, with no reactive power
The circuit has no real power at all
The circuit is short-circuited
The voltage and current are both zero

Question 20: How many watts are in 1 horsepower?

100 W
550 W
746 W
1000 W

Question 21: A motor is rated at 2 HP. How many watts is that?

746 W
1492 W
1600 W
2238 W

Question 22: A motor consumes 3730 watts of electrical power. Approximately how many horsepower is that?

2 HP
5 HP
7.5 HP
10 HP

Question 23: A facility has a low power factor (for example, 0.7). Compared to a facility with the same real power (kW) load at a power factor near 1.0, the low-PF facility requires:

Less apparent power and lower current
More apparent power (kVA) and higher current for the same useful work
Exactly the same apparent power and current
No real power at all

Question 24: A customer says their appliance "uses 500 watts per hour." What is technically incorrect about this statement?

Watts is already a rate (per unit time), so "watts per hour" double-counts time
Watts can only be used to describe DC circuits
The statement is completely correct as written
Watts should never be used to describe appliances

Question 25: A small business uses 3000 kWh of energy in a month, but its peak demand only briefly reached 25 kW. Which statement correctly describes how the utility would bill this?

The utility bills separately for the 3000 kWh consumed and may add a demand charge based on the 25 kW peak
The utility only cares about kWh and completely ignores peak kW
The utility bills 3000 kW as the demand figure
Demand and consumption are always billed as one identical number

EXAM CARD BASIC

Questions25

Time limit38 min

Pass score75%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 (NFPA 70)