Electrical Engineering Answers

A voltage source 𝑣(𝑡)=240 sin(314.16𝑡−20v°)𝑉 is connected to a load having an toa load having an impedance of Z. The resulting current through the load is 𝑖(𝑡)=15 sin(314.16𝑡+22.5°)A. Determine the circuit power factor and identify the elements that constitute the load, given that Z comprises of only two elements connected in series.

An electrical load operates at 120 Vrms The load absorbs an average of 8 kW at .lagging power factor of 0.8 The effective current I rms is:

select one:

a. 43.48 A 

b. 41.67 A 

c. 90.91 A 

d. 83.33 A 

e. 45.45 A

The current in a series circuit of R = 50 and L= 50 mH lags the applied voltage by 80 °,the angular frequency w is:

 Select one:

 a. 945 rad/s

 b. 473 rad/s

 c. 709 rad/s

 d. 405 rad/s

 e. 567 rad/s

An electrical load operates at 240 V rms. The load absorbs an average of 8 KW at lagging power factor of 0.6 The reactive power Q is:

 Select one:

а. 6.48L25.84°Ω

b. 5.04L45.57°Ω

с. 4.32L53.13°Ω

d. 5.76L36.87°Ω

е. З.бL60°Ω

A voltage V, =220L 30° Volt in a 3 phase ABC sequence system .Find VB:

A. 220 L-90° V

B. none of these

C. 220L -120° V

D. 220 L150° V

A 2000V, 100KW, 9000 rpm series connected DC motor has an armature resistance of 6Ω and a negligible field resistance.

(a) Determine the armature current at the rated load.

(b) Determine the copper loss at the rated load.

(c) Determine the mechanical loss knowing that the no-load armature current is 7 A at a speed of 9000 rpm.

(d) Determine the full load mechanical torque delivered to the load at a speed of 9000 rpm.

(e) Determine the efficiency of the motor.

A single phase 100 VA, 120/24 V transformer has the following results from the open-circuit and short-circuit tests.

Open circuit. Short Circuit

Voltage 120V 6V

Current. 0.1A 4.9A

Power 4.5W 16W

(a) Determine the circuit parameters (Rc, Xm, Req, Xeq) referred to the Higho Voltage side.

(b) Determine the efficiency of the transformer at full load with 0.8 power factora lagging.

Find the volume of the solid generated by revolving about the x-axis bounded by the curve, y2 = 9x and the line y = 3x

(a) Find fx(x,y), fy(x,y), fx(1,3), and fy(-2,4) for the given function. If 

𝑧 = 𝑓(𝑥, 𝑦) = 3𝑥

ଷ𝑦

ଶ − 𝑥

ଶ𝑦

ଷ + 4𝑥 + 9

(b) A firm estimates that it can sell Q units of its product with an advertising 

expenditure of x thousand dollars where 

𝑄 = 𝑄(𝑥) = −𝑥

ଶ + 600𝑥 + 25

i) Over what level of advertising expenditure is the number of units of 

product sold increasing? 

ii) Over what level of advertising expenditure is the number of units of 

product sold decreasing?