General Theory Study Prep – Questions With Solutions
What would the power factor be with these readings taken from a single
phase AC inductive circuit (230V - 11A - 2024W) Right Ans - 0.8
P (real/true power in W) / S (apparent power in VA) = P.F
What is the definition of the term impedance as applied to an AC circuit?
Right Ans - The total opposition (in Ohms) to the current flow in an AC circuit.
What is pull-out torque when applied to an AC induction motor? Right Ans
- The maximum value of torque the motor can produce.
What are the two main functions of the ballast in a fluorescent light fitting?
Right Ans - Provide a starting voltage
&
Limit current in the circuit.
What is the maximum resistance for the main earthing conductor? Right
Ans - No more than 0.5 Ohms.
A single-phase low voltage electrical installation has an earth fault loop
impedance of 0.2 Ohms when measured at the switchboard.
Calculate the prospective short circuit current. Right Ans - 1150 A
(230VAC / 0.2 Ohms = 1150 A)
A plug-in electric heater is designed for use on a 230/240 VAC supply.
The heater's resistance reads 26 Ohms when tested at the plug.
What is the supply voltage if the power dissipated is 2035W? Right Ans -
230V
, (2035W / 230VAC = 8.85A)
(2035W / 8.85A = 230VAC)
How does a single-phase AC permanently split capacity motor differ from a
single-phase AC capacitor start motor? Right Ans - It has no centrifugal
switch.
What do the figures AC80KA mean on an HRC fuse cartridge? Right Ans -
Alternating current 80000A maximum that the fuse can safely interrupt.
State the meaning of the term close excess current protection. Right Ans -
Will operate at 1.5 times rating within four hours.
Which single-phase AC induction motor would be best suited for a garage
door opening-closing operation? Right Ans - Permanent split capacitor
motor.
Define the term peak inverse voltage as applied to a semiconductor device.
Right Ans - Maximum voltage the semiconductor device can withstand in
reverse bias.
State the minimum resistance of an electrical installation that does not
contains MIMS heating elements. Right Ans - 1 M Ohms
A 6 pole 50Hz motor has a slip of 5%.
What speed does the motor run? Right Ans - 950 RPM
(60sec x 50Hz = 3000RPM
3000RPM / 3 pairs = 1000RPM
1000RPM x 0.05 = 50%slip
1000RPM - 50%slip = 950RPM).
What does BJT stand for when applied to semiconductors? Right Ans - No-
Polar Junction Transistor.
In what form is the voltage output from a PWM converter? Right Ans - A
series of rectangular pulses.
What would the power factor be with these readings taken from a single
phase AC inductive circuit (230V - 11A - 2024W) Right Ans - 0.8
P (real/true power in W) / S (apparent power in VA) = P.F
What is the definition of the term impedance as applied to an AC circuit?
Right Ans - The total opposition (in Ohms) to the current flow in an AC circuit.
What is pull-out torque when applied to an AC induction motor? Right Ans
- The maximum value of torque the motor can produce.
What are the two main functions of the ballast in a fluorescent light fitting?
Right Ans - Provide a starting voltage
&
Limit current in the circuit.
What is the maximum resistance for the main earthing conductor? Right
Ans - No more than 0.5 Ohms.
A single-phase low voltage electrical installation has an earth fault loop
impedance of 0.2 Ohms when measured at the switchboard.
Calculate the prospective short circuit current. Right Ans - 1150 A
(230VAC / 0.2 Ohms = 1150 A)
A plug-in electric heater is designed for use on a 230/240 VAC supply.
The heater's resistance reads 26 Ohms when tested at the plug.
What is the supply voltage if the power dissipated is 2035W? Right Ans -
230V
, (2035W / 230VAC = 8.85A)
(2035W / 8.85A = 230VAC)
How does a single-phase AC permanently split capacity motor differ from a
single-phase AC capacitor start motor? Right Ans - It has no centrifugal
switch.
What do the figures AC80KA mean on an HRC fuse cartridge? Right Ans -
Alternating current 80000A maximum that the fuse can safely interrupt.
State the meaning of the term close excess current protection. Right Ans -
Will operate at 1.5 times rating within four hours.
Which single-phase AC induction motor would be best suited for a garage
door opening-closing operation? Right Ans - Permanent split capacitor
motor.
Define the term peak inverse voltage as applied to a semiconductor device.
Right Ans - Maximum voltage the semiconductor device can withstand in
reverse bias.
State the minimum resistance of an electrical installation that does not
contains MIMS heating elements. Right Ans - 1 M Ohms
A 6 pole 50Hz motor has a slip of 5%.
What speed does the motor run? Right Ans - 950 RPM
(60sec x 50Hz = 3000RPM
3000RPM / 3 pairs = 1000RPM
1000RPM x 0.05 = 50%slip
1000RPM - 50%slip = 950RPM).
What does BJT stand for when applied to semiconductors? Right Ans - No-
Polar Junction Transistor.
In what form is the voltage output from a PWM converter? Right Ans - A
series of rectangular pulses.
