Calculate the power dissipated a resistance of 12 ohms connected to a 10v power supply.
8.33 watts
6.22 watts
5.92 watts
9.93 watts
The current in a coil changes from 5 amperes to 2 amperes in 50mS and induces a voltage of 30v into the coil. Calculate the value of the inductance of the coil.
0.1H
0.5H
1.1H
3H
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
A pure inductance 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 is used for underground power distribution?
MIMS
PILCSWA
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
Which one of the following is the most common earthing system in the UK?
TNC-S
TN-S
TN-C
TT
How is the primary earth connection made on a TT earthing system?
metallic sheath of the supply cable
earth rod into the ground
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
Calculate the synchronous speed of the rotating magnetic field in a 4-pole synchronous motor on 50Hz supply?
1500rpm
750rpm
3000rpm
1200rpm
How are the electrical connections made to the rotor of a 3-phase wound rotor induction motor?
commutator
slip rings
direct connection
via magnetic connection
What are the running characteristics of a 3-phase cage-rotor induction motor under constant load?
it runs above synchronous speed
it runs at synchronous speed
it runs at various speeds
it runs at constant speed
How can the direction of rotation be changed on a single phase capacitor start induction motor?
reverse the connections to the start winding
reverse the supply connections to the motor
reverse the capacitor connections
add a capacitor in parallel to the supply
What type of machine is a capacitor start capacitor run motor?
3-phase machine
synchronous machine
wound rotor machine
single phase machine
By what method are small 3-phase cage rotor induction motors started?
star/delta starter
DOL starter
rotor resistance starter
autotransformer starter
Newton is the SI unit for ?
force
pressure
mass
gravity
kilogram is the SI unit for ?
mass
pressure
weight
gravity
what is the SI unit for 'length' or 'distance'?
metre
millimetre
kilometre
feet/inches
Calculate the number of seconds in 12 minutes, 5 seconds.
720 seconds
725 seconds
695 seconds
700 seconds
What is the SI unit of measure for 'potential difference' or 'p.d' ?
amp
watt
weber
volt
What is the SI unit of measure for 'electromotive force' or EMF ?
newton
watt
weber
volt
What term is used to describe the 'amount of matter contained in a body' ?
mass
weight
force
compression
What type of force 'holds matter together' ?
cohesive force
compressive force
centrifugal force
shearing force
What type of force 'pushes matter together' ?
cohesive force
compressive force
centrifugal force
shearing force
What type of force 'acts away from the centres of two rotating masses' ?
cohesive force
compressive force
centrifugal force
shearing force
What type of force 'moves the face of one material over another material' ?
friction force
compressive force
centrifugal force
shearing force
What SI unit of measure is used for the 'rate that work is done'?
joule
watt
velocity
newtons per square metre
A 30 ohm resistance and a coil with inductance of 40 ohms are connected in series to a 100v 50Hz supply. Calculate the total impedance for the circuit.
70 ohms
50 ohms
10 ohms
170 ohms
A 30 ohm resistance and a coil with inductance of 40 ohms are connected in series to a 100v 50Hz supply. Calculate the total current for the circuit.
4 amps
2 amps
2.4 amps
4.8 amps
A 30 ohm resistance and a coil with inductance of 40 ohms are connected in series to a 100v 50Hz supply. Calculate the power-factor for the circuit.
0.64
0.60
0.68
0.66
A 30 ohm resistance and a coil with inductance of 40 ohms are connected in series to a 100v 50Hz supply. Calculate the 'true power' for the circuit.
80w
120w
100w
140w
A 10 ohm, a 30 ohm and a 12 ohm resistor are connected in series. Calculate the total resistance for the circuit.
52 ohms
62 ohms
50 ohms
48 ohms
A 1 ohm and a 4 ohm resistor are connected in parallel. Calculate the total resistance for the circuit.
0.8 ohms
0.2 ohms
5 ohms
1.25 ohms
A 10 ohm, a 30 ohm and a 12 ohm resistor are connected in series to a 10v d.c supply. Calculate the total current for the circuit.
0.19 amps
0.72 amps
1.5 amps
0.42 amps
A 1 ohm and a 4 ohm resistor are connected in parallel to a 10v d.c supply. Calculate the total current for the circuit.
12.5 amps
2 amps
1.25 amps
21.2 amps
What component can be added to large inductive loads to improve the 'power factor'?
inductors
capacitors
resistors
reactors
Current in an inductive AC circuit will......?
lead the supply voltage
lag behind the supply voltage
remain in unity with the supply voltage
become DC
An AC voltage has a peak voltage of 325v. Calculate the RMS voltage.
229.8v
206.9v
165.6v
189.8v
An AC voltage has a peak voltage of 325v. Calculate the AVERAGE voltage.
229.8v
206.9v
165.6v
189.8v
A lighting source emits 5000Cd and is 4m above a surface. Calculate the illuminance (lux) directly below the light source.
313 lux
1250 lux
223 lux
302 lux
A lighting source emits 5000Cd and is 4m above a surface. Calculate the illuminance (lux) 3m along the surface from directly below the light source.