In what equipment is a photon radiated when an electron leaves a hole ?
? LED? Photo-cell? Photo diode
What is the maximum number of electrons in shell N of an atom?
? 18? 32? 16
When an atom loses or gains an electron it is called ?
? a molecule? an ion? a current
The valence electron is ?
? the electron in outer shell of atom? the electron in inner shell of atom? a positive electron
Faraday's Law States that?
? the magnitude of the EMF is directly proportional to the magnetic flux? the magnitude of the EMF is indirectly proportional to the magnetic flux? the magnitude of the EMF is directly proportional to the rate of change of flux
Which of the following is 1 Amp?
? 1000 kA? 1000 mA? 1000 μA
Ohm's law states that ?
? resistance = current divided by e.m.f? current = e.m.f. divided by resistance? e.m.f. = current divided by resistance
The SI unit of work is ?
? Joules per metre? Kilogram metres-force? Joules per second (Watts)
Electromotive force is measured in?
? Watts? Ohms? Volts
The basis for transformer operation in the use of alternating current is mutual?
? inductance? capacitance? reactance
The S.I. unit of magnetic flux density is the ?
? Tesla? Weber? Henry
A shunt is used with?
? a voltmeter? an ammeter? an ohmmeter
The symbol for flux density is?
? MMF? H? B
One purpose of the commutator is to ?
? switch the direction of current flow every two cycles? switch the direction of current flow every cycle? switch the direction of the current flow every half cycle
The rotating part of a motor/generator is called ?
? commutator? armature? yoke
What is the purpose of the capacitor used in a single phase AC motor ?
? Smoothing? Provides a high starting torque? Changing direction of motor
In a two-phase induction motor there are ?
? 2 poles? 3 poles? 4 poles
In a synchronous motor, when the motor is running the slip is?
? 5%? 0%? 100%
In a 3 phase motor, if 1 phase is lost, the motor ?
? runs at 2 thirds speed? runs at 1 third speed? remains at the same speed
An AC generator is rated at 30 kVA at 0.8 Power Factor: this means that the maximum continuous output should not exceed?
? 30 KW? 24 KW? 37.5 KW
Delta wound line current is ?
? root 3 * phase current? equal to phase current? less than the phase current
Power factor of a generator is ?
? sin ø? tan ø? cos ø
The 'A' phase of a three phase power system is colour coded?
? blue? red? yellow
In a 2 phase generator, how far apart are the windings electrically?
? 90°? 180°? 45°
Band pass filter in a circuit?
? allows frequencies above a cut-off frequency to pass? allows frequencies below a cut-off frequency to pass? only allows a narrow band of frequency to pass
A capacitor in series and inductor in parallel make what kind of filter?
? Band pass? High pass? Low pass
Which is a high-pass filter ?
? Π type with series C and L? L type with series C and shunt L? L type with series L and shunt C
Aircraft autotransformers are of what type?
? Open core? Twin core? Laminated core
A 3-phase star-delta wound transformer gives?
? 30° phase shift? 90° phase shift? no phase shift
An autotransformer windings are?
? wired in parallel? on separate formers? connected
What causes a transformer to be noisy ?
? High coil resistance? An air gap in the core? High core losses
Which of the following would be used to calculate transformer turns ratio?
? primary turns ÷ secondary turns? primary turns × secondary turns? secondary turns ÷ primary turns
Eddy currents in a transformer can be reduced by ?
? laminations? using a single solid piece of metal? using a special non metallic material
A step up transformer has ?
? three windings? one winding? two windings
In this circuit applied voltage is ?
? V = IXL? V = IXC? V = I/R
The Sine wave signals of a circular time base are ?
? phase separated by 90°? in phase? phase separated by 180°
The controlling wave in a CRT is ?
? sawtooth? sinusoidal? square
If the frequency is increased in an AC circuit of pure resistance, the effect is?
? increased resistance? decreased resistance? nothing
The average value of 100 volts peak AC is ?
? 141.4 volts? 63.7 volts? 70.7 volts
Frequency (Hz) is the number of cycles per ?
? minute? revolution? second
A parallel circuit at resonance has?
? maximum impedance? zero impedance? minimum impedance
Prolonged reactive sparking in a DC generator could damage the?
? pole pieces? commutator? armature
Lines of magnetic flux pass from ?
? South to North? East to West? North to South
The unit of flux is the ?
? Weber? Ampere turns? Ampere turns / metre
The lines of magnetic flux from a magnet will?
? attract each other? repel each other? have no effect upon each other
Ferromagnetic materials can be magnetized ?
? within a band of temperatures? above a certain temperature? below a certain temperature
One microfarad is?
? 1 * 10-6 farads? 1 * 1012 farads? 1 * 10-12 farads
A capacitor has Brown, Black and Orange bands. It's value is ?
? 10 picofarads? 10 nanofarads? 100 picofarads
The charge on a capacitor is expressed as?
? the ratio Q/V? the product Q * V? the product C * V
One Picofarad is ?
? 1 * 1012 farad? 1 * 10-6 farad? 1 * 10-12 farad
In a power circuit, the purpose of an inductor is?
? to dampen power surges? to dampen current surges? to dampen voltage Surges
A thyristor ?
? has a positive temperature coefficient? if energized on, will switch on a circuit? if energized on, will switch off a circuit