Lesson 3: Solving Power Calculations

True or False: Resistors have a power rating in watts that should not be exceeded, or the resistor will be damaged.

True Because of the heat generated in electrical components, specifically resistors, a rating system has been developed so that components will not overheat during normal operation.

True or False: The work used in a heating circuit is called lost work because it cannot be used to move anything.

True The heat produced by the current through the resistance in the circuit is called I^2xR losses because it is heat lost in the system also known s watt losses.

True or False: Any time current flows through a resistance, heat is produced.

True The more current that is allowed to flow through a circuit, the hotter the circuit becomes. The heat is produced by the collision of free-flowing electrons with the fixed atoms. If the current is doubled, the heat will go up by 4x, and if its tripled it will go up 9 times.

True or False: When the current is doubled in a circuit, the power will increase to four times its original value.

True The total amount of heat produced in a conductor is directly proportional to the resistance times the square of the current. Heat = power.

True or False: Power is the rate at which work is done.

True Power = The rate of doing work = Work/Time

What formula can be used to find the current in a circuit if the power and resistance of the circuit are known? a. I = sqrt(P/R) b. I = sqrt(P) x R c. I = sqrt(P) / R d. I = sqrt(R)/P

a. I = sqrt(P/R)

Work is the product of the force and the distance that force moves something, and is measured in ? . a. foot-pounds b. horsepower c. time d. weight

a. foot-pounds Work = Force times distance. The unit of measurement is the foot-pound.

If one watt is equal to 0.00134 horsepower, then one kilowatt equals ? . a. 0.134 hp b. 1.34 hp c. 13.4 hp d. 134 hp

b. 1.34 hp

A resistor draws 12 amperes and has a resistance of 10 ohms. How much power, in kilowatts, is consumed? a. 0.144 kW b. 1.44 kW c. 14.4 kW d. 144 kW

b. 1.44 kW

A 50-ohm device draws 10 amperes. What is its load in kilowatts? a. 2 kW b. 5 kW c. 20 kW d. 50 kW

b. 5 kW

If 13,800 volts is delivered to a circuit that has a resistance of two ohms, how much power, in megawatts, is consumed in the load? a. 0.003450 MW b. 95.22 MW c. 380.88 MW d. 952.20 MW

b. 95.22 MW

If the voltage and resistance of a circuit is known, what equation is used to find power? a. P = I^2 x R b. P = E^2/R c. P = R/E^2 d. P = E^2R

b. P = E^2/R

One ? is equal to 33,000 foot-pounds per minute. a. ampere b. horsepower c. kilovolt d. kilowatt

b. horsepower Horsepower = The rate of doing work. 1 Horsepower = 33,000 foot-pounds / 1 minute 1 Horsepower = 550 foot-pounds / 1 second

The ? in an electrical circuit uses the power to convert electrical energy into some other form of energy. a. amperes b. load c. ohms d. voltage

b. load

A 50-ohm device draws five amperes. What is its load in kilowatts? a. 0.010 kW b. 0.250 kW c. 1.25 kW d. 12.5 kW

c. 1.25 kW

In addition to I^2R (power) losses, a five-horsepower motor uses ? of electrical power. a. 3,235 W b. 3,370 W c. 3,730 W d. 3,820 W

c. 3,730 W 5 horsepower x 746 watts / 1 horsepower = 3730 watts

A 1,000-watt lamp operates on 120 volts. How much current does it draw? a. 833 mA b. 1,200 mA c. 8.33 A d. 83.3 A

c. 8.33 A

A certain device operates on 12 volts and draws seven amperes. How much power does it consume? a. 0.58 W b. 1.71 W c. 84 W d. 588 W

c. 84 W

I^2R loss is often called ? . a. counter electromotive force (CEMF) b. electromagnetism c. heat loss d. hysteresis

c. heat loss Heat Loss - Heat loss is the most common loss in an electric circuit. The heat produced when current flows through resistance is referred to as heat loss. The power equation for heat loss is: P = I^2R

Electrical energy must be changed or converted to some other form of energy before there can be ? or watts. a. electromotive force (EMF) b. frequency modulation c. power d. voltage

c. power

A 2,000-watt circuit draws 0.833 amperes. What is its rated voltage? a. 4,160 mV b. 240 V c. 1,666 V d. 2,400 V

d. 2,400 V

? is one of the equations used to find power. a. P = E/I b. P = I/E c. P = I^2/R d. P = E x I

d. P = E x I

If the current and resistance of a circuit is known, what equation is used to find power? a. P = I^2/R b. P = R^2/I c. P = I x R d. P = I^2 x R

d. P = I^2 x R

Potential energy is measured in volts, and the unit of power is the ? . a. ampere b. hertz c. joule d. watt

d. watt The unit for potential energy is the volt, and the unit of power is the watt.

One horsepower is equal to 746 ? . a. foot-pounds b. joules c. volts d. watts

d. watts Watt - The unit of electrical power. One horsepower is equal to 745.7 W or approximately 746 watts.

True or False: Power is consumed when a voltage is applied to a circuit and current flows through the load.

True

True or False: The joule is a unit of energy used to measure the heat or work produced or consumed in a system.

True

True or False: Each kilowatt-hour is equal to 100 watt-hours.

False 1 kWh = 1000 kWh

True or False: The unit of measurement of electrical power is the volt.

False The unit for potential energy is the volt, and the unit of power is the watt.