Answer ALL questions. Look for any feedback given if you get an answer incorrect. Keep choosing an answer until you get it correct. CORRECT or INCORRECT answers are indicated at the TOP of the page. A score is given at the TOP of the page when the exercise has been completed.
What term is used to describe the ability of a capacitor to store a charge?
capacitance
charge
volume
capacitive reactance
Calculate the inductive reactance of a coil with inductance of 0.1H, connected to a 50Hz AC supply.
314.2 ohms
0.3142 ohms
3.142 ohms
31.42 ohms
What is the effect of an inductive load on an AC supply?
power factor lag
power factor lead
power factor unity
no effect
An inductive load with 10 ohms inductive reactance is connected to a 100v 50 Hz AC supply. Calculate the power dissipated in the circuit (ignoring any conductor resistance.)
1kW
100W
0kW
1W
The peak-to-peak voltage of a sinusoidal waveform is?
0.5 x peak
peak
2 x peak
4 x peak
Which electronic component has the function of detecting changes in light levels?
photo transistor
opto coupler
fibre optic cable
thyristor
A 3-phase 4-wire balanced load is connected to a 3-phase 4-wire supply. Each phase draws 65A from the supply. Calculate the neutral current?
0A
65A
195A
6.15A
What cable type was commonly used for underground power distribution?
MIMS
PILC
LSF
HOFR
A transformer has 1000v (V pri) and 200v (V sec). If current (pri) is 5A, calculate the secondary current.
5A
25A
1A
10A
What is the primary function of an isolator?
to make/break current only
to make/break voltage and current
to act an an on-load device
to act as an off-load device
How is the primary earth connection made on a TN-S earthing system?
direct connection to the earth using an earth electrode
metallic sheath of the supply cable
combined earth/neutral conductor
utilisation of water and gas pipes
Under what fault conditions does a RCD operate?
phase to earth fault
phase to neutral fault
open circuit fault in a phase conductor
open circuit in an earth conductor
What is the primary function of a fuse?
to protect circuit conductors from damage
to protect against electric shock
to protect appliances connected in the circuit
to protect against motor start-up currents
which one of the following makes use of the 'chemical' effect of electricity
motor
battery
thermo-couple
transformer
which one of the following makes use of the 'thermal' effect of electricity
motor
electric kettle
chromium plating
transformer
which one of the following makes use of the 'magnetic' effect of electricity
motor
electric kettle
chromium plating
transformer
calculate the total resistance for two 28 ohm resistors connected in series
56 ohms
65 ohms
28 ohms
zero ohms
calculate the total resistance for two 28 ohm resistors connected in parallel
56 ohms
14 ohms
28 ohms
zero ohms
calculate the current flow in a 10v DC circuit with a resistance of 8 ohms
18 A
2 A
1.25 A
2.25 A
an AC circuit is supplied at 230v 50Hz. If the impedance of the circuit is 0.9 ohms, calculate the prospective short-circuit current for the circuit.
256A
1150A
207A
10350A
calculate the inductive reactance of a 10mH coil connected to a 100v AC supply at 50Hz
100 ohms
42.4 ohms
3.14 ohms
56.2 ohms
a circuit is supplied at 230v 50Hz and draws 10A from the supply with a power-factor = 0.8. Calculate the 'apparent power' for the circuit
2300VA
1840VA
184VA
zero VA
a circuit is supplied at 230v 50Hz and draws 10A from the supply with a power-factor = 0.8. Calculate the 'true power' for the circuit