Applied Electricity Paper 2 , Nov/Dec. 2012

Questions:		1	2	3	4	5	6		Main

General Comments
Weakness/Remedies
Strength

Question 1

(a) Define the following with respect to alternating current:
           (i)        impedance;
           (ii)       reactance.
                                                '3.14Q.Q.          31 S· s.n. son.
r __ ..-J(OO)---1 f--r-=_::J--i---'
                                                       XL                   Xc                    R
.I II'
                L-- ___________________ ~ rv'\.- __________ -J
ioov, 50Hz
Fig. 3
(b) In Fig. 3, calculate the:
           (i)        impedance;
           (ii)       current, 1.

_____________________________________________________________________________________________________

Observation

The expected answers were:
            (a)(i)        Impedance is the total opposition afforded by an electric circuit to
the passage of alternating current.
                   (ii)     Reactance is the opposition afforded by a pure inductor or pure
capacitor to the passage of alternating current.
(b)(i) Impedance, Z = .JR2 + (XL - XC)2
= .J502 + (3.14 - 318.5)2
Impedance, Z = 319.3 Q
                  (ii)      Current, I = ¥
100
=--
319.29
Current, I = 0.313 A
306

The question was on Alternating Current Circuit Theory. It was well
attempted by candidates. The candidates' performance was reported to be
good.