A generator consists of a loop rotating in a static uniform magnetic field of 2 T oriented in a direction perpendicular to the axis of rotation. The loop is circular with radius 2 m. The peak emf generated is 5 V. At time t = 0 s, the emf was zero, but increasing. Write an expression for the emf as a function of time.

An ac resistance is higher than a dc resistance. True False

A single-phase, 120V(rms),60Hz source supplies power to a series R-L circuit consisting of R=10 and L=40mH. (a) Determine the power factor of the circuit and state whether it is lagging or leading. (b) Determine the real and reactive power absorbed by the load. (c) Calculate the peak magnetic energy Wint stored in the inductor by using the expression Wint=L(Irms)2 and check whether the reactive power Q=Wint is satisfied. (Note: The instantaneous magnetic energy storage fluctuates between zero and the peak energy. This energy must be sent twice each cycle to the load from the source by means of reactive power flows.)

An industrial load consisting of a bank of induction motors consumes 50 kW at a power factor of 0.8 lagging from a 220-V,60-Hz, single-phase source. By placing a bank of capacitors in parallel with the load, the resultant power factor is to be raised to 0.95 lagging. Find the net capacitance of the capacitor bank in F that is required.

A capacitor uses air as a dielectric and has a capacitance of 3 F. A dielectric material is inserted between the plates without changing the spacing, and the capacitance becomes 15 F. What is the dielectric constant of this material?

Convert the following instantaneous currents to phasors, using cos(t) as the reference. Give your answers in both rectangular and polar form. (a) i(t)=5002cos(t30) (b) i(t)=4sin(t+30) (c) i(t)=5cos(t15)+42sin(t+30)

You are working as an electrician in a large steel manufacturing plant, and you are in the process of doing preventive maintenance on a large DC generator. You have megged both the series and shunt field windings and found that each has over 10 M to ground. Your ohmmeter, however, indicates a resistance of 1.5 across terminals S1andS2. The ohmmeter indicates a resistance of 225 between terminals F1andF2. Are these readings normal for this type machine, or is there a likely problem? Explain your answer.

Varying the DC voltage to the rotor field changes the a. motor speed. b. power factor. c. phase excitation. d. slip.

In a pure capacitive circuit, does the current lead or lag the voltage?

Consider the circuit shown in Figure 2.23 in time domain. Convert the entire circuit into phasor domain.