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EAL ELEC3/008: Principles of electrical science

Total questions: 99

Worksheet time: 52mins

Name
Class
Date
1.

Solve the following calculation –20 ÷ –4

a)

–5

b)

5

c)

8

d)

6

2.

Which of the following is correct?

a)

22 kW = 22 × 10³ = 22,000 W

b)

22kW = 22 × 10³ = 2200 W

c)

22 kW = 22 × 10¹ = 22,000 W

d)

22 kW = 22 × 10² = 220,000 W

3.

Work out angle A.

a)

53.1°

b)

36.87°

c)

38.65°

d)

90°

4.

What is the result of the following calculation 20 + 4 × 3 = ?

a)

72

b)

32

c)

83

d)

64

5.

What is the result of the following calculation (42 × 4) + (6 ÷ 3) -2 = ?

a)

42

b)

56

c)

420

d)

168

6.

What is the result of the following calculation 10000 × 100?

a)

100,000

b)

1000

c)

10,000

d)

1,000,000.

7.

What is the result of 83 ?

a)

8

b)

24

c)

512

d)

16

8.

What is the resulting fraction?

a)

b)

c)

d)

9.

Transpose the equation in order to find I

a)

b)

c)

d)

10.

What kind of angle is shown here?

a)

right angle

b)

straight line

c)

obtuse

d)

acute.

11.

If a = 4, c = 8, b = ?

a)
6.92
b)

8.94

c)

48

d)

80

12.

Calculate the mean, median and mode of the following numbers: 4, 8, 7, 2, 6, 8

a)

mean = 5.83; median= 4.5; mode= 8

b)

mean = 5; median= 9; mode= 8

c)

mean = 5.83; median= 6.5; mode= 8

d)

mean = 5.83; median= 9.5; mode= 7

13.

What kind of triangle is shown?

a)

scalene

b)

right angle

c)

equilateral

d)

isosceles

14.

Lighting circuits are permitted 3% allowance regarding the amount of voltage that can be dropped. What is 3% of 230 V?

a)

11.5 V

b)

12 V

c)

1.304 V

d)

6.9 V

15.

Solve the following 3³ × 3⁶.

a)

3³

b)

3¹⁸

c)

3¹²

d)

3⁹

16.

What kind of electronic devices conduct when gated and are used in motor control applications?

a)

diode

b)

transistor

c)

diac

d)

thyristor

17.

What kind of device changes its resistance with a corresponding temperature change?

a)

thyristor

b)

triac

c)

thermistor

d)

transistor

18.

A reed switch uses which effect of electricity?

a)

heat

b)

chemical

c)

magnetism

d)

fusion

19.

Which component is appropriate to be used to stop heat damage to a relay?

a)

diode

b)

capacitor

c)

transistor

d)

resistor

20.

Which of the following is correct?

a)

diode = rectifier

b)

capacitor = rectifier

c)

transistor = rectifier

d)

resistor = rectifier

21.

Which of the following is correct?

a)

diodes are used as transformers

b)

capacitors are used in smoothing circuits

c)

transistors are used as electronic switches

d)

resistors are used as amplifiers

22.

If a diode is forward biased then it will pass current from:

a)

cathode to anode

b)

anode to cathode

c)

base to collector

d)

gate to anode

23.

An inverter:

a)

changes a sinusoidal waveform to direct current

b)

changes d.c. to a.c.

c)

changes a.c. to d.c.

d)

changes light to electricity

24.

What kind of electronic device combines two zener diodes and will allow current flow in either direction once it reaches a certain value?

a)

diode

b)

transistor

c)

diac

d)

thyristor

25.

NPN and PNP are types of?

a)

diode

b)

transistor

c)

diac

d)

thyristor

26.

What kind of device reduces its resistance when light falls on it, allowing current to flow?

a)

photo cell

b)

zener diode

c)

light emitting diode

d)

light dependent resistor

27.

What kind of device converts light energy into electrical energy and is used in burglar alarms?

a)

photo cell

b)

zener diode

c)

light emitting diode

d)

light dependent resistor

28.

What kind of semi-conductor device acts like a thyristor but allows current flow in either direction when it is gated?

a)

diac

b)

zener diode

c)

thyristor

d)

triac

29.

If three capacitors are connected in parallel and are rated at 34 μF, 24 μF and 17 μF, calculate the total capacitance of the circuit.

a)
75 μF
b)

17.5 µF

c)

175 µF

d)

0.75 µF

30.

If two capacitors are connected in series and are both rated at 10 μF, calculate the total capacitance of the circuit.

a)
5 μF
b)

7 µF

c)

15 µF

d)

20 µF

31.

What kind of rectification circuit would produce the output shown?

a)

partial rectification

b)

single diode

c)

half-wave rectification

d)

full wave rectification

32.

What kind of rectification circuit would produce the output shown?

a)

partial rectification

b)

single diode

c)

half-wave rectification

d)

full wave rectification

33.

An electronic device that emits red, green, or yellow light when a current of about 10 mA flows through it is a:

a)

light dependent resistor (LDR)

b)

light-emitting diode (LED)

c)

semiconductor diode

d)

thermistor

34.

What kind of capacitor is polarized?

a)

flux capacitor

b)

electric capacitor

c)

electrolytic capacitor

d)

polaroid capacitor

35.

The opposition to current flow in an a.c. resistive circuit is called:

a)

resistance

b)

inductance

c)

reactance

d)

impedance

36.

The opposition to current flow in an a.c. capacitive or inductive current is called:

a)

resistance

b)

inductance

c)

reactance

d)

impedance

37.

The total opposition to current flow in any a.c. circuit is called:

a)

resistance

b)

inductance

c)

reactance

d)

impedance

38.

An a.c. series circuit has an inductive reactance of 4 Ω and a resistance of 3 Ω. The impedance of this circuit will be:

a)

5 Ω

b)

7 Ω

c)

12 Ω

d)

25 Ω

39.

An a.c. series circuit has a capacitive reactance of 12 Ω and a resistance of 9 Ω. The impedance of this current will be:

a)

3 Ω

b)

15 Ω

c)

20 Ω

d)

108 Ω

40.

The inductive reactance of a 100 mH coil when connected to a 50 Hz supply will be:

a)

5 Ω

b)

20 Ω

c)

31.42 Ω

d)

31.42 kΩ

41.

The capacitive reactance of a 100 μF capacitor when connected to a 50 Hz supply will be:

a)

5 Ω

b)

20 Ω

c)

31.8 Ω

d)

31.8 kΩ

42.

A circuit with poor power factor causes:

a)

the supply voltage to fall

b)

the supply voltage to increase

c)

more current consumption from the supply

d)

less current consumption from the supply

43.

If uncorrected, poor power factor means the circuit conductors have to be:

a)

made smaller

b)

made bigger

c)

made longer

d)

made shorter

44.

Calculate the design current in a domestic single phase supply that has a power rating of 5 kW and operates with a power factor of 0.8.

a)

17.39 A

b)

27.17 A

c)

46 A

d)

36.8 A

45.

Calculate the circuit current in a three-phase supply (400 V) that has a power rating of 5 kW and operates with a power factor of 0.8.

a)

9.02 A

b)

12.5 A

c)

15.6 A

d)

7.21 A

46.

The effect of an inductor is to cause the current in a circuit to:

a)

be in phase with the voltage

b)

lead the voltage

c)

lag the voltage

d)

double the voltage

47.

Which of the following is used to improve power factor?

a)

resistor

b)

inductor

c)

capacitor

d)

transformer

48.

In order to carry out bulk correction of power factor, where is the correction item fitted?

a)

across the line conductor

b)

across the supply

c)

across the neutral

d)

across each individual load

49.

A disadvantage of using synchronous motors to correct for power factor is:

a)

system uses more voltage

b)

system uses more current

c)

the cost of synchronous motors

d)

the cost of capacitors

50.

Impedance is represented by:

a)

R

b)

Z

c)

XL

d)

XC

51.

Power factor is shown through which relationship?

a)

sine (s = O/H)

b)

cosine (A/H)

c)

tangent (T = O/A)

d)

cosine^-1

52.

Which of the following represents perfect power factor?

a)

1

b)

0.99

c)

0.5

d)

0

53.

Given that Cos = R/Z if the resistance is 10 Ω and the impedance is 10.2 Ω, work out the power factor.

(a)  

54.

A star connected system has a line current of 3 A. Work out the phase current.

a)

3.5 A

b)

6 A

c)

3 A

d)

16 A

55.

A star connected system has a line voltage of 600 V. Work out the phase voltage.

a)

3.5 kV

b)

346 V

c)

250 V

d)

346 kV

56.

A delta connected system has a line voltage of 600 V. Work out the phase voltage.

a)

600 V

b)

346 V

c)

600 mV

d)

346 kV

57.

A delta connected system has a phase current of 30 A. Work out the line current.

a)

30 A

b)

51.96 A

c)

45 A

d)

16 A

58.

A GLS lamp is associated with:

a)

regeneration effect

b)

incandescence

c)

poor colour rendering

d)

being very inefficient

59.

A tungsten halogen lamp is associated with:

a)

regeneration effect

b)

incandescence

c)

poor colour rendering

d)

goes from blue to nearly white

60.

A fluorescent lamp is associated with:

a)

power factor correction capacitor

b)

incandescence

c)

choke

d)

starter

61.

The amount of light reflected on to a surface at any angle from the light source is calculated by using the:

a)

inverse-square law

b)

maintenance factor

c)

cosine law

d)

lumen method

62.

The intensity of a light is measured in:

a)

candela

b)

flux

c)

candarel

d)

lux

63.

What advantage does the inclusion of the halogen gas have inside a tungsten lamp?

a)

increases life expectancy

b)

increases ceramic

c)

enhances power factor

d)

produces a regeneration effect

64.

What kind of lamps are often used in street lighting?

a)

low-pressure mercury

b)

cfl

c)

low-pressure sodium

d)

high-pressure sodium

65.

When a GLS lamp is at the end of its life, what often happens?

a)

high circuit current, protective device operates

b)

low circuit current, protective device operates

c)

high circuit current, protective device remains set

d)

low circuit current, protective device remains set

66.

What is the common name for a low-pressure mercury vapour lamp?

a)

spot lamp

b)

fluorescent lamp

c)

high frequency

d)

low tungsten

67.

Why is there a capacitor connected across the supply terminals of a fluorescent lamp?

a)

it improves efficiency

b)

it assists with electromagnetic interference

c)

it reduces power factor issues

d)

it reduces starting currents

68.

The light output of a high-pressure mercury vapour lamp is:

a)

blue white but cold light with fairly good colour rendering

b)

very yellow light with poor colour rendering

c)

warm yellow light with good colour rendering

d)

cold white light with very good colour rendering properties, making it suitable for colour photography.

69.

The light output of a high-pressure sodium lamp is:

a)

blue white but cold light with fairly good colour rendering

b)

very yellow light with poor colour rendering

c)

warm yellow light with good colour rendering but can also be white

d)

cold white light with very good colour rendering properties, making it suitable for colour photography.

70.

The light output of a metal halide lamp is:

a)

blue white but cold light with fairly good colour rendering

b)

very yellow light with poor colour rendering

c)

warm yellow light with good colour rendering

d)

cold white light with very good colour rendering properties, making it suitable for colour photography.

71.

The light output of a low-pressure sodium lamp is:

a)

blue white but cold light with fairly good colour rendering

b)

very yellow light with poor colour rendering

c)

warm yellow light with good colour rendering

d)

cold white light with very good colour rendering properties, making it suitable for colour photography.

72.

What changes UV light to visible white light inside a fluorescent lamp?

a)

the gas

b)

the starter

c)

the phosphorous inside

d)

the power factor capacitor

73.

Which of the following is a measure of how well a light source produces visible light?

a)

luminous efficacy

b)

glass efficiency

c)

phosphorous efficiency

d)

luminous efficiency

74.

With reference to the Inverse Square Law, if you move an object from 3 m to 6 m what would happen to the amount of light that is reflected on the surface?

a)

decrease

b)

decrease by a factor of 2

c)

decrease by a factor of 4

d)

decrease by a factor of 8

75.

A street lamp has a luminous intensity of 2000 cd and is suspended 5 m above the ground. The illuminance on the pavement below the lamp will be:

a)

40 lx

b)

80 lx

c)

400 lx

d)

800 lx

76.

Which of the following motors can be used with either a.c. or d.c. supply?

a)

d.c. series

b)

shunt

c)

universal

d)

compound

77.

Applications for series d.c. motor include:

a)

an electric train

b)

a microwave oven

c)

a central heating pump

d)

an electric drill

78.

Which of the following applies to a d.c. shunt motor?

a)

provides high starting torque

b)

constant speed irrespective of the load

c)

used where speed is not important

d)

used in electric drills

79.

Which of the following applies to a d.c. compound motor?

a)

provides low starting torque

b)

can provide constant speed

c)

can provide high starting torque

d)

used with elevators

80.

One application for an a.c. induction motor is:

a)

an electric train

b)

a microwave oven

c)

a central heating pump

d)

an electric drill

81.

One application for a shaded pole a.c. motor is:

a)

an electric train

b)

a microwave oven

c)

a central heating pump

d)

an electric drill

82.

Which of the following motors is the cheapest?

a)

capacitor start

b)

capacitor start/run

c)

permanent split capacitor (PSC) motors

d)

split phase

83.

Which of the following motors has low starting currents, low starting torques and no starting mechanism?

a)

capacitor start

b)

d.c. series

c)

permanent split capacitor (PSC) motors

d)

split phase

84.

Which of the following motors is used on fans, gate operators, garage-door openers?

a)

capacitor start

b)

d.c. series

c)

permanent split capacitor (PSC) motors

d)

split phase

85.

Which of the following motors is used to start loads that are hard to start such as lathes, compressors and small conveyor systems?

a)

capacitor start

b)

capacitor start/run

c)

permanent split capacitor (PSC) motors

d)

split phase

86.

Which of the following would be dangerous to start up without load?

a)

capacitor start

b)

d.c. series

c)

permanent split capacitor (PSC) motors

d)

split phase

87.

Capacitor-start capacitor-run induction motors are usually:

a)

three-phase machines

b)

single phase machines

c)

synchronous machines

d)

shaded pole machines

88.

Squirrel cage motors are:

a)

three-phase machines

b)

single phase machines

c)

asynchronous machines

d)

constant speed

89.

Which of the following would be used to start up motors <5 kW?

a)

direct-on-line starter

b)

star delta starter

c)

rotor-resistance starter

d)

autotransformer starter

90.

Which of the following would be used to start up motors with a rating of 5 kW to 20 kW but against either light or no load?

a)

direct-on-line starter

b)

star delta starter

c)

rotor-resistance starter

d)

autotransformer starter

91.

Which of the following would be used on motors involved with heavy loads?

a)

direct-on-line starter

b)

star delta starter

c)

rotor-resistance starter

d)

autotransformer starter

92.

Which of the following is used to start up squirrel cage motors?

a)

direct-on-line starter

b)

star delta starter

c)

rotor-resistance starter

d)

autotransformer starter

93.

An electric motor is connected to a motor starter to:

a)

improve the efficiency of the motor

b)

provide the initial starting torque for the motor

c)

reduce heavy starting currents

d)

provide overload and no-volt protection.

94.

An electromagnetic device that can operate one or several contacts is known as:

a)

a transformer

b)

a diode

c)

a relay

d)

an inductor

95.

An electromagnetic device that uses a small electrical signal to switch a much larger power circuit is known as:

a)

a transformer

b)

a diode

c)

a relay

d)

an inductor

96.

An electromagnetic device used in switching heavy duty current applications is known as:

a)

a transformer

b)

a diode

c)

a contactor

d)

an inductor

97.

A relay is made up of:

a)

switch and contacts

b)

solenoid and contacts

c)

spring and contactor

d)

field and contactor

98.

A component that is magnetized only when an electric current flows through it is called:

a)

a switch

b)

a permanent magnet

c)

an electromagnet

d)

a motor

99.

Which effect of electricity is used by an inductor?

a)

magnetic

b)

heat

c)

chemical

d)

light

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