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M3 quiz Kempy

Total questions: 62

Worksheet time: 1hrs 19mins

Name
Class
Date
1.

When capacitors is arrange in series (3 capacitors), the equivalent capacitance C is

a)

C = C1 + C2 + C3

b)

1/C = 1/C1 + 1/C2 + 1/C3

c)

C = QV1 + QV2 + QV3

d)

C = CR1 + CR2 + CR3

2.

Connecting capacitors in parallel effectively causes the _____ ________

a)

distance between the plates , increase

b)

distance between the plates , decrease

c)

plate area increase

d)

plate area decrease

3.
Capacitors well hold a charge until
a)
the applied voltage drops to zero
b)
5 time constants
c)
an external discharge path is provided
d)
1 time constant
4.
Capacitance is inversely proportional to 
a)
a charge
b)
dielectric thickness 
c)
plate area
d)
applied voltage
5.
When a capacitor discharges
a)
current reverses direction compared to the charge current
b)
it acts like a DC open
c)
the electrostatic charge remains 
d)
plate voltage increases
6.
The amount of charge that a capacitor can accept is determined by 
a)
It's capacity C=Q/V
b)
the plate area
c)
the dielectric thickness
d)
all of the above
7.

Which of the graphs below shows the characteristics for the circuit shown?

a)
b)
c)
d)
e)
8.

Which of these circuit symbols represents a band pass filter

a)
b)
c)
d)
e)
9.

Which of these circuit symbols represents a high pass filter

a)
b)
c)
d)
e)
10.

The critical frequency is defined as the point at which the response drops ________ from the passband.

a)

- 3 db

b)

-20 db

c)

-6 db

d)

- 40 db

11.

A ________ filter significantly attenuates all frequencies below fc and passes all frequencies above fc.

a)

Low pass

b)

High Pass

c)

Band Pass

d)

Band Stop

12.

What kind of filter is shown in the figure ?

a)

Low Pass Filter

b)

High Pass Filter

c)

Band pass filter

13.

-------------------- is a circuit which can be designed to modify , reshape or reject all undesired frequencies .

a)

Filter

b)

oscillator

c)

Amplifier

d)

Rectifier

14.

which of these circuits matches its equivalent schematic symbol?

a)

b)

c)

d)

15.

The force exerted by a magnetic field depends on 3 things. What is the 3rd?

1) Magnetic flux density 2) Current 3) ...

(a)  

16.

What is the unit of magnetic flux density?

(a)  

17.

What is the unit of magnetic flux density?

(a)  

18.

What happens if you cut a magnet in half?

a)

Nothing

b)

The magnets repel

c)

There will be two magnets

19.
What can demagnetize a magnet?
a)
A. high altitudes
b)
B. high temperatures
c)
C. low altitudes 
d)
D. low temperatures
20.

A magnet is dropped through a coil connected to a millivoltmeter as shown. The voltmeter needle moves to the right showing a positive reading.


Which of these will make the voltmeter move to the left?

a)

Drop the south pole through first

b)

Add more turns to the coil

c)

Move the magnet slowly through the coil

d)

Use a stronger magnet

21.

A magnet is dropped through a coil connected to a millivoltmeter as shown. The voltmeter needle moves to the right showing a positive reading.


Which of these will make the voltmeter reading smaller but still positive?

a)

Drop the south pole through first

b)

Add more turns to the coil

c)

Move the magnet slowly through the coil

d)

Use a stronger magnet

22.

The force on a wire can be made stronger in several ways. Which one of these will not work?

a)

Increase the current

b)

Use stronger magnets

c)

Use a coil with many turns

d)

Make the wire thicker

23.

The diagram shows a coil of wire with a current flowing through it in the direction shown by the arrows. The coil is between 2 magnets as shown.


Using Fleming's Left hand Rule, which way will the coil move?

a)

upwards

b)

downwards

c)

rotate clockwise

d)

rotate anticlockwise

24.

Some magnets are easily magnetised when placed in a magnetic field, and then quickly lose their magnetism once the field is removed. These materials are used in electromagnets, and are called...

a)

soft magnetic materials

b)

hard magnetic materials

c)

temporary magnets

d)

partial magnets

25.

Which of these is not a magnetic material?

a)

aluminium

b)

steel

c)

nickel

d)

iron

26.
Which of the following may be done to increase the force felt during the motor effect?
a)
Increase the current, length of wire in the field or the strength of the magnetic 
b)
Increase the voltage, length of wire in the field or the strength of the magnetic 
c)
Increase the current, increase the voltage or increase the strength of the magnetic field
d)
Increase the resistance in the wire or increase the magnetic field strength
27.
The current in the green wire flows from the left to the right. What direction does the wire move?
a)
Up 
b)
Down
c)
Into the page
d)
Out of the page
28.
Which rule do we use to predict the direction a current carrying wire will move in a magnetic field?
a)
Fleming's Left Hand Rule
b)
Fleming's Right Hand Rule
c)
Faraday's Left Hand Rule
d)
Faraday's Right Hand Rule
29.
Why does a compass needle point north?
a)
The compass is a bar magnet
b)
Because north is up
c)
Because it's magic
d)
It lines up with the Earth's magnetic field
30.
Which two methods may be employed for speed control of DC machines?
a)
Current control and reactance control
b)
Voltage control and inductance control
c)
Voltage control and field control
31.
Where are compensating windings located in DC machines?
a)
In parallel with the interpoles
b)
On the commutator
c)
Within the main poles
d)

Within the armature windings

32.
What is the cause of reactive sparking?
a)
The meeting of the coils and brushes within the neutral zone.
b)
The meeting of the coils and brushes outside the neutral zone.
c)
The positioning of the brushes on the magnetic neutral axis.
d)

Poor contact of the bushes with the commutator

33.
What is armature reaction?
a)
The impact of the armature cross-field on the main field.
b)
The back EMF produced in the armature.
c)
The reaction to the torque produced by the stator.
d)

Impact of the resistive force of the load on the armature angle with reference tot he main field

34.
How is the excitation winding and the armature winding connected in a Shunt Wound DC Motor?
a)
Series
b)
Crossed
c)
Intermittent
d)
Parallel
e)

Series-parallel

35.
Which part provides the power supply for the armature in a DC machine?
a)
Excitation winding
b)
Pole shoe
c)
Commutator
d)

The rotating rectifying diode pack.

36.
How is the rotation direction of a DC machine changed?
a)
By interchanging the supply leads.
b)
By reversing the current direction in the armature winding or the excitation winding.
c)
By reversing the current direction in the stator winding.
d)

By increasing the frequency of the supply voltage

37.
What is the purpose of the excitation winding in a DC machine?
a)
To generate a static magnetic field in the stator.
b)
To generate a static magnetic field in the rotor.
c)
To increase the output power.
d)

To generate a Rotating Magnetic Field (RMF) in the stator

38.

With reference to Torque in a dc machine:


The magnitude of the force is proportional to

a)

The strength of the magnetic field, Flux Density,

The current in the conductor,

The length of the conductor influenced by the magnetic field.

b)

The value of back emf,

The current in the conductor,

The length of the conductor influenced by the magnetic field.

c)

The value of back emf,

The current in the field windings,

The length of the conductor influenced by the magnetic field.

d)

The value of back emf,

The current in the conductor,

The number of poles on the stator.

39.

How can Back emf be calculated

a)

Eb=Vs−IaRaE_b=V_s-I_aR_a

b)

Eb=Vs+IaRaE_b=V_s+I_aR_a

c)

Eb=VsIaRaE_b=\frac{V_s}{I_aR_a}

d)

Vs=EbIaRaV_s=\frac{E_b}{I_aR_a}

40.

Which of these statements are true regarding the laminated iron core in a Rotor?

Select 1 or more answers.

a)

It holds the armature winding in slots

b)

It forms part of the magnetic circuit

c)

It increases the eddy currents in the armature, therefore increases the magnetic flux

d)

It forms part of the electric circuit

e)

It forms the return path for the magnetic field

41.

What component is represented by label K

a)

Armature Windings

b)

Commutator

c)

Pole Piece

d)

Drive shaft

e)

Yoke

42.

What is the purpose of the commutator?

a)

To reverse the current in the armature

b)

To reverse the current in the field windings

c)

To protect the slip ring from damage

d)

To allow constant motion of the rotor

e)

To allow the motor to be used as a generator

43.

What is the advantage of a series field motor?

a)
Low starting torque and inability to operate at variable speeds
b)
High starting torque and inability to operate at variable speeds
c)
Low starting torque and ability to operate at fixed speed
d)
High starting torque and ability to operate at variable speeds
44.

What is the advantage of a shunt field motor?

a)
It has a high efficiency at low speeds
b)
It is not affected by changes in the load
c)
It requires less maintenance
d)

It maintains constant speed even when the load changes.

45.

What type of motor is best suited as a starter motor?

a)

Shunt field motor

b)

Series field motor

c)

Compound motor

d)
Stepper motor
46.

How is the direction of rotation in a dc machine changed?

a)
By increasing the resistance in the circuit
b)
By reducing the number of windings in the armature
c)
By adding more voltage to the circuit
d)
By reversing the polarity of the applied voltage or by reversing the connections to the field winding or armature.
47.

what is the purpose of the excitation winding in a dc machine?

a)
To increase the machine's weight
b)
To cool down the machine
c)
To create the magnetic field necessary for the operation of the machine.
d)
To reduce the efficiency of the machine
48.

Why are interpoles fitted to main poles of DC machines?

a)
To increase armature reaction and commutation problems.
b)
To reduce armature reaction and commutation problems.
c)
To decrease the efficiency of the machine.
d)
To make the machine more prone to overheating.
49.

Which component in a dc machine machine provides the power supply for the armature?

a)

Transformer and rotating diode pack

b)
Commutator and brushes
c)

Excitation winding

d)

Field winding

50.

What effect would increasing the armature current have on the armature cross field?

a)
Reverse
b)
No effect
c)
Weaken
d)
Strengthen
51.

What does a commutator do in a dc machine?

a)
Increases the speed of the armature
b)
Regulates the voltage in the field windings
c)
Controls the temperature of the machine
d)
Reverses the direction of current in the armature windings
52.

What does a commutator do in a dc machine?

a)
Increases the speed of the armature
b)
Regulates the voltage in the field windings
c)
Controls the temperature of the machine
d)
Reverses the direction of current in the armature windings
53.

What does a commutator do in a dc machine?

a)
Increases the speed of the armature
b)
Regulates the voltage in the field windings
c)
Controls the temperature of the machine
d)
Reverses the direction of current in the armature windings
54.

If the frequency of the ac supply is increased what would happen to the value of the inductive reactance (XL) within a series LR circuit

a)

XL would increase

b)

XL would decrease

c)

XL would remain the same

55.

If the frequency of the ac supply is increased what would happen to the value of the capacitive reactance (XC) within a series LR circuit

a)

XC would increase

b)

XC would decrease

c)

XC would remain the same

56.

What is the relationship between the peak voltage (Vp) and the root mean square voltage (Vrms) in a sinusoidal wave?

a)

Vp = √2 * Vrms

b)

Vp = 2 * Vrms

c)

Vp = 0.5 * Vrms

d)

Vp = Vrms

57.

on the graph showing a sinusoidal wave, what is being represented by the letter a?

a)

Vp-p

b)

Vp

c)

Vmean

d)

Vrms

58.

What is the main characteristic that distinguishes AC from DC?

a)

In AC the amount (size) of voltage remains constant.

b)

In AC the direction (polarity) of current remains constant.

c)

In AC the amount (size) of both voltage and current changes with time.

d)

In AC the direction (polarity) of both voltage and current changes with time.

59.

Which statement accurately describes common AC?

a)

The changes in voltage and current never repeat.

b)

The average voltage and current are always positive.

c)

The voltage and current vary sinusoidally with time.

d)

The current remains constant over time.

60.

What is the unit of frequency?

a)
Hertz (Hz)
b)

Volt (V)

c)

Watt (W)

d)

Seconds (s)

61.

What is the amplitude of an AC waveform?

a)

The average value of voltage or current over a full cycle.

b)

The peak value of voltage or current.

c)

The instantaneous value of voltage or current.

d)

The root mean square value of voltage or current.

62.

What defines a square waveform?

a)

It rises quickly to a particular amplitude, remains constant for a time period, and drops fast at the end.

b)

It is a waveform with a symmetrical shape and equal rise and fall times.

c)

It oscillates between positive and negative peak values.

d)

It has a steady rate of change of voltage over each half cycle.

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