Deck 8: Formulas

Question 1

A motor takes a current of 27.5 amperes per leaf on a 440-volt, three-phase circuit. The power factor is 0.80. What is the load in watts? Round the answer to the nearer whole watt. For a three-phase circuit:

Answer 1

16766

Question 2

Find the impedance of a coil with 5.5 ohms resistance and 8.2 ohms reactance. Round the answer to the nearer hundredth.

Answer 2

9.87

Question 3

The temperature of a motor rises to C above room temperature. The room temperature is C. What will a Fahrenheit thermometer read? Carry the answer to one decimal place.

Answer 3

168.8

Question 4

If a 25-horsepower motor takes 96 amperes at full load, and the motor efficiency is 90%, what is the terminal voltage? Express the answer to the nearer hundredth.

Question 5

If is the unknown resistance of the Wheatstone bridge arrangement shown in the figure, find the value of this unknown resistance. Carry the answer to one decimal place.

Question 6

The total capacitance ( C ) is directly proportional to the product of the dielectric constant ( k ) and plate area ( A ) and inversely proportional to the thickness ( d ) of the dielectric.

A) $C = \frac { k d } { A }$
B) $C = \frac { k A } { d }$
C) $C = \frac { k } { d A }$
D) $C = \frac { d } { k A }$

Question 7

In a circuit, what current does a 220-volt, 5-horsepower motor receive if the efficiency of the motor is 80%? Express the answer to the nearer hundredth.

Question 8

Find the power used in the single-phase circuit shown. Carry the answer to three decimal places.

Question 9

The resonant frequency ( $f _ { r }$ ) of a circuit containing both inductance ( L ) and capacitance ( C ) may be found by the reciprocal of two pi ( $2 \pi$ ) Hint:((The reciprocal is 1/ $2 \pi$ )) multiplied by the square root of the product of the inductance and capacitance.

A) $f _ { r } = \sqrt { L C } / 2 \pi$
B) $f _ { r } = 1 / 2 \pi \sqrt { L C }$
C) $f _ { r } = L / 2 \pi \sqrt { L C }$
D) $f _ { r } = C / 2 \pi \sqrt { L C }$

Question 10

A three-phase, three-wire circuit delivers 175 amperes at a voltage of 220 volts with a 0.85 power factor. What is the kilowatt load to the nearer hundredth?

Question 11

The current ( I ) in an electrical circuit is directly proportional to the voltage applied ( E ) and inversely proportional to the circuit impedance.

A) $I = \frac { Z } { E }$
B) $E = \frac { V } { I }$
C) $I = \frac { E } { Z }$
D) $I = \frac { E ^ { 2 } } { Z }$

Question 12

The internal resistance of five cells is 1.8 ohms each. The cells are connected as shown in the diagram to a 2-ohm resistance. What current, to the nearer hundredth, exists in the circuit?

Question 13

An electrical motor has a degree of efficiency ( Eff ) equal to the ratio of its useful output power ( $P _ { 0 }$ ) to the input power ( $p _ { 1 }$ ) required to operate it.

A) $E f f = \frac { P _ { 0 } } { P _ { 1 } }$
B) $E f f = \frac { P _ { 1 } } { P _ { 2 } }$
C) $E f f = \frac { P ^ { 2 } 0 } { P _ { 1 } }$
D) $E f f = \frac { P _ { 1 } } { P _ { 0 } }$

Question 14

A motor takes 38 amperes on a 220-volt circuit. Find the horsepower output (hp) of the motor shown with an efficiency of 90%. Express the answer to the nearest hundredth.

Question 15

What is the resistance of if the total resistance of the parallel circuit shown is 3.2 ohms?

Question 16

The electrostatic force ( F ) between two plates of a charged capacitor is directly proportional to the product of the charges ( $q_ 1$ and $q_2$ ) on each plate and inversely proportional to the square of the distance ( d ) between the plates.

A) $F = \frac { q _ { 1 } } { d q _ { 2 } }$
B) $F = \frac { d } { q 1 q 2 }$
C) $F = \frac { q 1 q 2 } { d }$
D) $F = \frac { q 1 q 2 } { d ^ { 2 } }$

Question 17

Determine the horsepower output to the nearer hundredth for the motor in the circuit shown.

Question 18

If a current of 4.5 amperes exists, what is the impedance of a circuit having a voltage of 110 volts across it? Express the answer to the nearer hundredth.

Question 19

Solve the equation for the current ( I ) required by a motor when the horsepower, percent efficiency of the motor, and the voltage are known. $$\begin{aligned}h p = \frac { ( E ) ( I ) ( E f f ) } { 746 } \quad \text { where } & l = \text { current in amperes } \\& E = \text { voltage in volts } \\& E f f = \text { efficiency of motor } \\& h p = \text { horsepower }\end{aligned}$$

A) $I = \frac { 746 } { E \times E f f \times h p }$
B) $I = \frac { 746 ( h p ) } { E \times E f f }$
C) $I = \frac { ( h p ) } { 746 E \times E f f }$
D) $I = \frac { E \times E f f } { 746 ( h p ) }$

Question 20

Find the resistance of 240 feet of number 10 copper wire with a cross-sectional area ( ) of 10,380 circular mils. Express the answer to the nearer hundredth.

Question 21

The four dry cells are connected in series as shown. Find the total resistance. Carry the answer to three decimal places.

Question 22

A 60-volt electric time clock circuit with several clocks connected in parallel has a 2-wire line voltage drop of 12.5 volts when the circuit is closed. Using Ohm s law, find the total resistance of the 2-wire line if a current of 10 amps exists. Carry the answer to two decimal places.

Question 23

Find the total resistance in ohms if the current in the circuit is 2.82 amps and the voltage is 120 volts. Carry the answer to two decimal places.

Question 24

Choose the correct formula to solve the problem. A circuit has a voltage of 120 volts and a current of 7.5 amps. Find the amount of power used.

Question 25

One 2-wire section of a 24-volt watchman clock signal system is operated through a 450-foot length of lead covered cable drawing 2 amps. The size of the conductor is number 18, and the diameter is 40.3 mils. What is the resistance of one conductor? Express the answer to the nearer whole number.

Question 26

Find the value of the current for the circuit if . Carry the answer to two decimal places.

Question 27

Choose the correct formula to solve the problem. A one-horsepower motor uses 900 watts when connected to a circuit. The motor receives a current of 3.4 amps. Find the voltage to one decimal place that is across the circuit.

Question 28

Find the total resistance ( ) of the circuit shown.

Question 29

What is the current in amperes in a 3-phase circuit when the load is 67.5 horsepower, the efficiency is 90%, the voltage is 440 volts, and the circuit power factor is 0.80? Round the answer to the nearer hundredth.

Question 30

A lamp with a resistance (hot) of 50 ohms is connected across 120 volts. What current does the lamp receive?

Question 31

A lamp requires a current of 0.94 amps when connected to a circuit with a voltage of 120 volts. Find the resistance in ohms of the lamp. Carry the answer to two decimal places.

Question 32

What is the frequency in hertz (Hz) of the current furnished by an alternator having 8 poles and running at a speed of 900 revolutions per minute?

Question 33

Find the length of a copper wire 0.104 inch in diameter if it has a resistance of 3.1 ohms ( 1 mil = 0.001 inch). Carry the answer to two decimal places.

Question 34

If the cross-sectional area of a wire is 16,510 circular mils, what is the diameter (d) of the wire? Carry the answer to two decimal places. Cross-sectional area = where d = diameter in mils

Question 35

The four dry cells are connected in series as shown. Find the voltage. Carry the answer to three decimal places. Hint: You may need to find total resistance first.

Question 36

Find the total resistance ( ) of the three low voltage relay coils. Round the answer to the nearer hundredth.

Question 37

What voltage is required to force a 4.5-amp current through an electric iron having a resistance of 25.5 ohms?

Question 38

Choose the correct formula to solve the problem. A 500-watt electric iron is connected to 120 volts. How many amps of current to three decimal places does the iron take?

Question 39

What size conductor should be used in a 2-wire system to service a load of 6,500 watts, 150 feet from the generator? The voltage at the load is 120 volts, and the voltage drop should not exceed 2.5 volts. Round to a whole number.

Question 40

Choose the correct formula to solve the problem. How many watts will a motor use if the voltage is 240 volts and the motor is drawing 40 amps of current?

Question 41

What is the impedance ( Z ) of a coil with 84 ohms resistance ( R ) and 500 ohms reactance (X)? Round the answer to the nearer ohm.

Question 42

A cell has a voltage (E) of 2.1 volts, an internal resistance (r) of 0.9 ohms, and is connected to an electromagnet with a resistance (R) of 0.3 ohm. What current, in amps, will the electromagnet receive? Carry the answer to two decimal places.

Question 43

Choose the correct formula to solve the problem. What voltage will be required to create a current of 5 milliamps through a wire-wound resister having a resistance of 750 ohms? Carry the answer to two decimal places.

Question 44

What current will exist in a 3,000-watt electric iron when a voltage of 240 volts is maintained? Carry the answer to one decimal place.

Question 45

A circuit uses 216.2 watts and draws a current of 1.88 amps. Find the resistance. Express the answer to the nearer hundredth ohm. and

Question 46

Find the number of watts in the armature of a generator having an internal resistance of 0.3 ohm and a voltage of 6 volts across the resistance.

Question 47

A motor uses 5,595 watts. Find the horsepower load of the motor. Carry the answer to one decimal place.

Question 48

Choose the correct formula to solve the problem. A 550-watt electric iron has a voltage drop of 112 volts. What current to the nearer hundredth amp exists in the iron?

Question 49

The temperature of a commutator is C. Express this temperature in degrees Fahrenheit.

Question 50

What voltage is necessary if 1.5 amps exist in a 60-watt lamp?

Question 51

Choose the correct formula to solve the problem. A 1,500-watt electric iron is connected to 120 volts. How many amps will the iron take? Carry the answer to one decimal places.

Question 52

A motor takes a current of 8 amps per leg on a 440-volt, 3-phase circuit. The power factor is 0.75. What is the load in watts? Carry the answer to two decimal places.