Basic Electrical Theory: Unit 9 - Electrical Formulas

What does it cost per year (at 8 cents per kWh) for the power loss of a 12 AWG conductor (100 ft long) that has a total resistance of 0.40 ohms and a current flow of 16A? Formula: Cost per Year = Power for the Year in kWh x $0.08

$72

What is the resistance of the circuit conductors when the conductor voltage drop is 7.20V and the current flow is 50A? Formula R = E/I

0.14 ohms

The total circuit resistance of two 12 ASG conductors (each 100 ft long) is 0.40 ohms. If the current of the circuit is 16A, what is the power loss of both conductors? Formula: P = Isquared x R

100W

What is the power loss in watts of a conductor that carries 24A and has a voltage drop of 7.20V? Formula: P = I x E

175W

What is the power consumed by a 10 kW heat strip that's rated 230V, if it's connected to a 115V circuit? Formula: P = Esquared/R

2.50kW

What is the conductor power loss for a 120V circuit that has a 3 percent voltage drop and carries a current flow of 12A? Formula: P = I x E

43W

What is the voltage drop of two 12 AWG conductors (0.40 ohms) supplying a 16A load, located 100 ft from the power supply? Formula: E voltage drop = I x R

6.40 volts

What is the approximate power consumed by a 20kW heat strip rated 230V, when connected to a 208V circuit? Formula: P = ESquared/R

8.20kW

The formulas in the power when apply to _________ and ______________.

DC, & ac with unity power factor

The Ohm's Law Formula, I = E/R, states that current is ____________ proportional to the voltage, and ______________ proportional to the resistance.

Directly, inversely

In dc circuit, the only opposition to current flow is the physical resistance of the material. This opposition is called "reactance" and is measured in ohms. True or false?

False

The best conductors, in order of their conductivity, are gold, silver, copper and aluminum. True or False?

False

The polarity and the output voltage from a dc power source changes direction. One terminal will be negative and the other will be positive. True or False?

False

The polarity and the output voltage from an ac power source never change direction. True or False?

False

The voltage applied to a resistor dramatically affects the power consumed by that resistor because power is affected in direct proportion to the voltage. True or False?

False

The circuit resistance includes the resistance of _____________, _______________ and __________________.

Power source, conductors & load

Conductance or conductivity is the property of metal that permits current to flow. The best conductors in order of their conductivity are:

Silver, copper, gold, aluminum

Conductance is the property that permits current to flow. True or False?

True

Direct current is used for electroplating, street trolley and railway systems, or where a smooth and wide range of speed control is required for a motor-driven application. True or False?

True

Often the resistance of the power source and conductor are ignored in circuit calculations. True or False?

True

The major advantage of ac over dc is the ease of voltage regulation by the use of a transformer. True or false?

True

When working any formula, the key to finding the correct answer to follow these four steps: Step 1:Know what the question is asking you to find. Step 2:Determine the knowns of the circuit. Step 3:Select the formula. Step 4:Work out the formula calculation. True or False?

True

Ohm's Law demonstrates the relationship between circuit ___________, __________ and _______________.

intensity, EMF, & resistance.

According to the Electron Current Flow Theory, electrons leave the ____________ terminal of the source, flow through the conductors and load(s), and return to the ________________ terminal of the source.

negative, positive

Power in c circuit can be either "useful" or "wasted." Wasted work is still energy used; therefore it must be paid for, so we call this "____________"

power losses

An electrical circuit consists of the ________, ____________, and ___________.

power source, conductors, & load.

In an ac circuit, the factors that oppose current flow are ___________________, _________________, and ____________________.

resistance, inductive reactance, & capacitive reactance.