# DCM 102 ELECTRICAL AND ELECTRONIC PRINCIPLES.

UNIVERSITY EXAMINATIONS: 2014/2015
EXAMINATION FOR THE DIPLOMA IN COMPUTER
MAINTENANCE
DCM 102: ELECTRICAL AND ELECTRONIC PRINCIPLES
DATE: NOVEMBER, 2014 TIME: 1½HOURS

QUESTION ONE
(a) Using a simple diagram explain the free electrons found in materials [6 Marks]
(b) Discuss the three main types of electrical materials [6 Marks]
(c) Calculate the colour code for the following resistor values [4 Marks]
i. 200 Ohms +/-10%
ii. 6.3 KOhms +/-5%
(d) “The total resistance in a parallel circuit is less than that of the smallest resistor in the
network.” Explain. [4 Marks]
QUESTION TWO
(a) Give three instruments used in electronics and the use of each [6 Marks]
(b) Convert the following to the corresponding values [6 Marks]
i. 11000V to KV
ii. 0.0098A to mA
iii. 560000 to KOhms
(c) Given the following colour codes calculate the minimum and maximum values of the
resisitors [6 Marks]
i. red, red, black, gold
ii. green, blue, orange
(d) Give the difference between a circuit breaker and a fuse [2 Marks]
QUESTION THREE
(a) State Ohms Law [2 Marks]
(b) Using simple diagrams compare and contrast series and parallel circuits [4 Marks]
(c) Name 2 types of capacitors, inductors and resistors [6 Marks]
(d) In Q3 (b) above show the various parameters that should be consider when selecting
the devices for an application [3 Marks]
(e) Give the construction and operation of one of the devices in Q3(b)
QUESTION FOUR
(a) List the four main components of an electric circuit [2 Marks]
(b) Define the terms below [6 Marks]
i. current
ii. resistance
iii. power
(c) For the circuit below calculate [12 Marks]
i. total resistance
ii. current through R1, R2 and R6
iii. voltage across R3, R4 and R5
QUESTION FIVE
(a) Briefly explain how dc voltage is produced by dry cells. Neat diagrams may be
drawn. [6 Marks]
(b) Explain the operation of a simple half wave rectifier. The schematic diagram and
waveforms must be drawn. [8 Marks]
(c) Two resistors of equal resistance are connected in series and the current measured
(Is). They are now connected in parallel and total current (Ip) measured. Calculate the