問題一覧
1
Changing the rate of current flow in a coil causes a voltage to be induced in the same coil. This effect is known as
self inductance
2
A permanent magnet
requires no external power source
3
The periodic time of an AC waveform is
the time taken for completion of one cycle
4
Which component causes the circuit current to lead the voltage
capacitor
5
The max percentage of space which may be occupied by the cables within a trunking system is
45%
6
All the conductors associated with a particular circuit should be contained in the same steel conduit to
minimise induced eddy currents
7
Which of the following is the best method of fixing a metal socket outlet box to a masonry surface
plastic plug and screw
8
In a three phase supply system the phase angle between each phase is
120°
9
It is common practice to install more than one lighting circuit in a building because
some lighting will be available should one circuit fail
10
If the capacitor is connected across the mains in a fluorescent fitting becomes disconnected the lamp
will light normally
11
Mineral insulated cables are sometimes provided with an overall covering of pvc to
prevent corrosion of the copper sheath
12
In agricultural and horticultural premises the type of sockets used
shall comply with EN60309
13
Once a single phase capacitor start motor is running at rated speed the start winding
is taken out of circuit by a centrifugal switch
14
The thermal overload in a motor control circuit should be set at
the full load current of the motor
15
The second digit in the IP system indicates the degree of protection against
ingress of water
16
Which of the following will change the direction of rotation of a three phase induction motor
change over any two of the three phases
17
Which of the following is a three phase induction motor
a delta connected induction motor
18
Which is a single phase induction motor
a capacitor start, capacitor run motor
19
The normally closed auxiliary contact on the thermal overload on a motor control circuit forms part of the
control circuit
20
A thermal overload protective device is operated by an increase in
current
21
The power on the indicator lamp belongs to the
signal circuit
22
The symbol for inductance is
xL
23
A conductor is made to move between north and south poles of a permanent (horse shoe) magnet, cutting the lines of force and inducing and emf into the conductor
dynamic induction
24
Frequency in AC means
the number of cycles passed in one second
25
Which represents a full cycle of ac
360°
26
Which formula expresses the relationship between voltage and current
Vp/Vs=Is/Ip
27
The efficiency of a transformer is
98%
28
Transformers are categorized as follows
class 1 and class 2 equipment
29
Continuity test of pvc should read
infinity
30
Flourescent lamps are also known as low pressure mercury vapour lamps. What is the life expectancy of these lamps
8,000 to 12,000 hrs
31
Another name of a ballast used in a fluorescent light is
a choke
32
A capacitor is installed in the starter unit for the purpose of
radio interference suppression
33
XPLE insulated cable is suitable for use between the temperature of
-25 and +75 degrees
34
The CSA of the protective conductor in NYM-J cable is
equal to the csa of the current carrying conductors
35
The first number of the IP system indicates protection
against the ingress of foreign bodies
36
Overload currents of short duration occur when
a motor is starting
37
A single phase induction motor that delays the flow of its starting current in its run winding relative to the flow of current in its start winding is called
a split phase induction motor
38
The overload of a DOL motor control circuit should be set at
the full load current of the motor
39
The MCB type used on motor control circuit is
type c
40
Which part of the motor control circuit does the float level switch belong
control circuit
41
A transformer core is laminated to reduce
iron loss