Chapter 17, Problem 4P

Question 1:  Answer A, 6EH is wrong Question 7: Answer D is wrong

A.With the aid of a diagram, describe fringing, and explain the impact that it has on the relevant magnetic circuit parameter. B. A coil of 1500 turns give rise to a magnetic flux of 2.5 mWb when carrying a certain current. If this current is reversed in 0.2 s, what is the average value of the e.m.f. induced in the coil?   C.Define Mutual Inductance.Two coils are connected in series and their total inductance is measured as 0.12 H, and when the connection to one coil is reversed, the total inductance is measured as 0.04 H. If the coefficient of coupling is 0.8, determine:The self-inductance of each coil, and the mutual inductance between the coils.

comparing Lenz's law and the left hand generator rule, which of these is the more important fundamental principle?

a) An iron ring, having a mean circumference of 250 mm and a cross-sectional area of 400 mm², is wound with a coil of 70 turns. Using the following data, calculate the current required to set up a flux of 510µWb in the ring. H (A/m) 350 600 1250 B (T) 1.0 1.2 1.4 b) Calculate also: i. The inductance of the coil at the current obtained in Question 2 (a) above. ii. The self-induced e.m.f. if this current is switched off in 0.005 s. Assume that there is no residual flux.

A balanced three-phase, 1351-V, 60-Hz, A-connected source feeds a balanced Y- connected load with a per-phase impedance of 360 + j150 Q as shown in Figure 1. Calculate: i. The readings on each of the wattmeters ii. The power factor of the load using the wattmeter readings. NOTE: i. ii. Let VAN be the reference phasor, and the phase sequence be ABC anticlockwise. Assume the voltage-drop on the conductors between the source and the load to be zero volts. V b V₁ W 000 000 ; A 360 + j150 360 + j150 4 b 0000 000 B 360 + j150 C W₂ Figure 1

a) Three 30 2 resistors are arranged as shown in Figure 1 below. They are connected to a 480 V three-phase supply. The phase sequence is RYB anticlockwise. Calculate: i. The total power drawn by the circuit using the phase parameters. ii. The power read by each wattmeter. b) If Za, one of the 30 2 resistors, is now removed from the circuit, calculate: R- i. The line currents: IR, Iv, and la ii. The power read by each wattmeter. iii. The total power drawn by the two resistors. W₁ Be- W2 www 'R 22 12 B Figure 1