Exam 8: Formulas

Find the total resistance ( $R _ { T }$ ) of the three low voltage relay coils. Round the answer to the nearer hundredth.

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. $E _ { 1 }$

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

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? f= where f= frequency in hertz P = number of pairs of poles N = revolution per minute

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. $X _ { L }$

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. I=P/E CM=KNLI/

Choose the correct formula to solve the problem. $a ^ { 2 } = b ^ { 2 } + c ^ { 2 }$ $E = I R$ $R = E / I$ 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. $P = E I$

$E _ { L I N E } = \sqrt { E_ R ^ { 2 } + E_ X ^ { 2 } }$ Find the value of the current for the circuit if $R _ { 1 } = 0$ . Carry the answer to two decimal places.

What is the resistance of $E _ { \text {LINE } }$ if the total resistance $E_ X$ of the parallel circuit shown is 3.2 ohms? $E _R$

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. R= where R= resistance in ohms L= length in feet d= diameter in mils K=10.8 (constant)

Find the resistance of 240 feet of number 10 copper wire with a cross-sectional area ( $X _ { L } = \sqrt { Z ^ { 2 } - R ^ { 2 } }$ ) of 10,380 circular mils. Express the answer to the nearer hundredth.

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

$E _ { L I N E } = \sqrt { E _R ^ { 2 } + E _X ^ { 2 } }$ 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.

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. $I = E / R + r$

Choose the correct formula to solve the problem. $O P = V _ { 1 } ^ { 2 } + V _ { 2 } ^ { 2 } + 2 \left( V _ { 1 } \right) \left( V _ { 2 } \right) \cos \theta$ $I = E / R$ $E = I R$ $R = E / I$ $P = I ^ { 2 } R$ $I = P / E$ $E = P / I$ $R = E ^ { 2 } / p$ $P = E ^ { 2 } / R$ $I = \sqrt { P / R }$ $E = \sqrt { P R }$ $R = P / I _ { I ^ { 2 } }$ A 500-watt electric iron is connected to 120 volts. How many amps of current to three decimal places does the iron take?

A motor uses 5,595 watts. Find the horsepower load of the motor. Carry the answer to one decimal place. $h p = P / 746$

The temperature of a commutator is $20 ^ { \circ }$ C. Express this temperature in degrees Fahrenheit. ${ }^{\circ} \mathrm{C}=5 / 9\left(F-32^{\circ}\right)$

What voltage is necessary if 1.5 amps exist in a 60-watt lamp? $P = E I$

$E _ { L I N E } = \sqrt { E _R ^ { 2 } + E _X ^ { 2 } }$ 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.

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. $\theta = 360 t _ { i } f$