301 Revision questions and answers new 2013.pptx

7/28/2019 301 Revision questions and answers new 2013.pptx

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301 Revision

Jan 2013


2/24

The speed of a d.c shunt machine can be variedby placing a variable resistor in series with the

field winding. The speed will increase when the

a/ resistance is increasedb/ resistance is decreasedc/ resistance is disconnectedd/ load is increased


3/24

Thermal trips in direct online motor starters areto provide protection against

a/ short circuitb/ starting overloadc/ open circuitd/ continuous overload


4/24

A single phase a.c series motor is constructedwith

a/ field and armature windings connected inseries by a commutatorb/ a cage rotor short circuited

c/ field windings connected in seriesd/ stator and rotor windings connected inseries by slip-rings


5/24

The rotor conductors of a three phase cagerotor induction motor are constructed of solid

conductors

a/ shorted at each end by rings b/ connected to the supply by a commutatorc/ connected to the supply by slip ringsd/ forming a star connection


6/24

An eight pole 50Hz three phase induction motorhas a synchronous speed of

a/ 50 r/sb/ 25 r/sc/ 12.5 r/sd/ 6.25 r/s


7/24

If a single loop of wire forms the armature of asimple d.c generator, the emf generated in one

of the coil is given by the formulaa/ e = 2 60

NP

b/ e = 2 N60 P c/ e = 2 NP

60d/ e = 2 NP

60


8/24

A 4 pole 3 phase generator is to produce a 50 Hzoutput. It must be driven at a speed of

a/ 16.6 r/sb/ 20 r/sc/ 25 r/sd/ 50 r/s


9/24

In a single phase installation, short circuitcurrent flows when the impedance between the

phase and neutral is

a/ greater than 100 M ohmsb/ less than 1 M ohmc/ less than 100 M ohmsd/ negligible


10/24

BS88-3 fuses are often used for the protection of motor circuits because this type of fuse

a/ can discriminate between overload andstarting currents b/ can withstand high current overloads for longperiods

c/ will disconnect the circuit quickly if a very smalloverload occursd/ is cheaper than a BS 3036 fuse


11/24

When connecting an electric motor to anearthed conduit system using flexible conduit,the CPC for the motor must be provided by

a/ the flexible conduit itself b/ a separate conductor installed within the

flexible conduitc/ a separate conductor and local earth rodd/ the motor fixing bolts


12/24

In the TN-S supply system, the earthingconductor is connected between the main

earthing terminal and the

a/ earth electrodeb/ incoming cable sheathc/ water piped/ incoming neutral


13/24

In a 3 phase and neutral TT system, the mainisolator must be able to disconnect from thesupply the

a/ three phase conductors and neutral conductor b/ three phase conductors only

c/ neutral conductor onlyd/ three phase, neutral and earthing conductors


14/24

A short circuit fault in the primary winding of anauto transformer can cause the

a/ secondary voltage to oppose the primaryvoltageb/ secondary voltage to appear across theprimary terminalsc/ primary voltage to appear across thesecondary terminalsd/ primary voltage to become less than thesecondary voltage


15/24

Busbar trunking used to supply electricity todifferent floors in a multi-story building is

referred to as a

a/ vertical riserb/ rising mainc/ electrical riserd/ rising supply


16/24

The supergrid operates at a voltage of

a/ 33kVb/ 132kVc/ 275kVd/ 400kV


17/24

A silicon chip on which a number of diodes andtransistors are formed is called

a/ an integrated circuit b/ transistor diode/chipc/ multi semi-conductord/ discrete circuit


18/24

When a single semi-conductor diode isconnected across an a.c supply having a peakvalue of 10V, the peak inverse voltage (PIV)

across the diode is

a/ 7.071Vb/ 14.14Vc/ 20Vd/ 40V


19/24

A series a.c circuit has a resistance of 10 ohms,inductive reactance 5 ohms and capacitivereactance 2 ohms. The impedance of the

combination is

a/ 0.427 ohmsb/ 4.27 ohmsc/ 8.3 ohmsd/ 10.44 ohms (approx)


20/24

When a capacitor, inductor and resistor areconnected in series across an a.c supply the

impedance of the circuit is given by whatformula?


21/24

When a circuit having a resistance and inductance isconnected to an a.c supply, a current of 10A flows.If the in phase component of current is 6A the

power factor of the circuit is

a/ 0.5b/ 0.6c/ 0.8d/ 0.9


22/24

The relationship between the potentialdifference (V) the charge (Q) and a capacitance

C is

a/ Q = C/Vb/ C = V/Q c/ Q = CVd/ C = QV


23/24

Two coils have a mutual inductance of 100 microhenries. When the current in the primary coilchanges at the rate of 1000A/s, the e.m.f

induced in the secondary coil is

a/ 0.01Vb/ 0.1Vc/ 1.0Vd/ 10V


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The resistance of a material at constanttemperature is calculated using what formula?

R = p la

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301 Revision questions and answers new 2013.pptx