Electric current is described as a flow of
Which one of the following identifies the sources of an electromotive force?
Atomic, magnetic, thermal
Chemical, atomic, thermal
Chemical, magnetic, thermal
Chemical, magnetic, atomic
When the current passing through a conductor is increased, the conductor’s temperature will:
The SI unit Henry is used for
Ohm is the SI unit of measurement for:
The SI unit for frequency is the
Resistance, potential difference and electrical current are expressed in the same order as units of:
Ohms, Volts, Amperes
Ohms, Watts, Amperes
Ohms, Volts, Watts
Watts, Volts, Ohms
Transpose the formula Z² = R² + X² to make R² the subject.
R² = X² – Z²
R² = Z² – X²
R² = Z² + X²
R² = X² x Z²
If the resistivity of aluminium is 2.65 x 10 -8 /metre, the resistance of a 65 metre length of 16mm2 aluminium conductor is:
For the circuit shown, the total resistance is:
For the circuit shown, the power dissipated by the 15Ω resistor is:
The power dissipated in the circuit shown on the right would be:
When measuring current flow in a d.c. circuit, an ammeter must be connected:
using a rectifier
using a VT
in series with the load
in parallel with the load
Instrument B in the figure on the right measures the:
voltage drop caused by R2
voltage drop caused by R3
current through R1
current through R2
The strength of the magnetic flux produced when current flows in a conductor can be increased by:
increasing the current
decreasing the current
reversing the current
using alternating current
Which one of the following shows the correct poles of the electromagnet when current flows in the direction shown?
What would be the effect on magnetic flux for the two equal, current-carrying conductors shown?
The magnetic field would halve in strength, flowing in opposite directions
The magnetic fields around each of the conductors would rotate independently
The magnetic fields around the conductors would cancel each other out
The magnetic field around the conductors would double in strength and flow in the same direction
A conductor of a simple alternator is 0.4m long and cuts a magnetic field with a magnetic flux density of 1.5 tesla at a velocity of 30m/s. The EMF induced in the conductor will be:
Which one of the following is the supply frequency if a sine wave has a periodic time of 20 milliseconds?
Refer to the figure shown. What does value A indicate?
Average value of the waveform
Periodic time of the waveform
RMS value of the waveform
Peak amplitude of the waveform
Which one of the following quantities can be described as a force?
The formula shown is used to determine the force required given mass and acceleration. Which one of the following would be the acceleration for a mass of 20kg having a force of 10N applied? F = m x a
The power required to raise a mass of 8kg across a distance of 10m in 40 seconds is approximately:
A motor produces an output of 1.2kW when the input is 1.4kW; its efficiency is:
When used to ‘inch’ heavy equipment across the floor, a crowbar is being:
Which one of the following instruments would be used to measure the line voltage for the star connected load?
In a four-wire, three phase system the phase voltage is 220v. The line voltage will be:
Which one of the following is the phase voltage for a star connected load if the line voltage is 400V?
Which one of the following instruments would be used to measure the line current for the delta connected load?
The line current feeding a delta load is 52A. The delta phase current will be:
The phase current in a delta load is 10A. The line current will be:
A balanced three phase star connected load draws a line current of 24A per phase. Which of the following is the approximate value of neutral current?
A d.c. motor in which the current remains constant in the field winding but varies in the armature winding is called:
a compound machine
an armature machine
a shunt machine
a series machine
If a single loop of wire connected to a commutator is rotated in a permanent magnetic field, the voltage measured at the commutator will be:
The diagram shows a simple motor, indicating the field poles and direction of current flow. In which one of the following directions would the conductor move?
In a 400v to 4,000v step-up transformer the ratio of primary to secondary turns ratio will be:
Which one of the following components would cause current and voltage to behave as indicated in the sine wave shown?
The power triangle shown gives the relationship between powers in an a.c. circuit. Which one of the following is the unit used to measure Apparent power?
A circuit dissipates 3kW at a power factor of 0.7 when connected to a 230V a.c. supply. The current flowing in the circuit will be:
Power factor correction in circuits having lagging power factors can be achieved by connecting:
inductors across the load
resistors across the load
resistors in series with the load
capacitors across the load