ELEX 1 COCOON TESTS Flashcards
1
Q
A type of electricity in which charges are moving.
A
Current
2
Q
What is considered as the fourth state of matter?
A
Plasma
3
Q
A particle that retains all the properties of an element is called:
A
Atom
4
Q
Which of the following is considered as positive charge?
A
Protons and nucleus
5
Q
The identity of an element can be found commonly on what part of an atom?
A
Nucleus
6
Q
What is the atomic number of an element with 5 electrons but 4 protons?
A
4
7
Q
What is the mass of an electron?
A
0.91x10^-30 kg
8
Q
An atom has a single proton and a single neutron. The element is:
A
Hydrogen
9
Q
Which of the following shell has the lowest energy level?
A
K
10
Q
How many electrons reside on the P shell of copper?
A
0
11
Q
If the number of electrons on the outermost shell of an atom is 3, then 3 is the:
A
Valence
12
Q
Which of the following valence is the best conductor?
A
2
13
Q
Which of the following is the best conductor?
A
Silver
14
Q
When an atom loses an electron it becomes:
A
Both cation and ion
15
Q
Materials with more free electrons are called:
A
Conductor
16
Q
A material with a valence of exactly 4 is:
A
Semiconductor
17
Q
Insulators don’t easily allow electric current to flow because:
A
None of the choices because the answer is that valence electrons of electrons tend to stay on their orbit
18
Q
It is the band where the outermost electron/s are occupying
A
Valence band
19
Q
Which of the following electrons are the most energetic?
A
Free electrons
20
Q
Where do free electrons exist?
A
Conduction band
21
Q
Which of the following material has the smallest energy gap?
A
Conductor
22
Q
The band that exist between two allowed band is called:
A
Forbidden band
23
Q
As the electron orbits closer to the nucleus, it becomes ________.
A
Less energetic
24
Q
The two forces acting on electrostatics are?
A
Attraction and repulsion
25
Which is true in electrostatics?
None of the choices because electrostatics deals with charges not poles
26
In the first law of Coulomb's Law for electrostatics, the force between charges is:
Attractive or repulsive
27
It states that the force between charges is inversely proportional to the square of the distance between them.
Second Law of Coulomb's Law
28
Permittivity is the ability of a material to _______ the formation of electric field.
Resist
29
Which of the following is unitless?
Relative permittivity
30
It is the field around a charge body.
Electric field
31
Because electric field is invisible, its strength and polarity can be represented with:
Electric lines of force
32
Electric lines of force are polarized from:
Positive to negative
33
An ability of a charged body to attract or repel another charged body expressed in Volts.
Electrical potential
34
The electrical force that attract or repel another charged body expressed in Volts
EMF
35
The difference of potential between two points in an electrical circuit.
Potential difference
36
1 Volt is equivalent to:
1J of work to move 1C of charge
37
A directional movement of charged bodies.
Electrical current
38
1A is equivalent to:
1C of charge passing at a point in 1s
39
Which of the following limits the flow of charge in an electrical circuit?
resistance
40
Which of the following is inversely proportional to Resistance?
diameter of the conductor
41
Which of the following offers a positive temperature coefficient
concrete nail
42
A property of a material to attract iron?
Magnetism
43
The space surrounding a magnet where magnetic forces act.
magnetic field
44
Because magnetic field is invisible, its strength and polarity can be represented with:
magnetic lines of force
45
Magnetic lines of force is polarized from:
North to South
46
Which is true about magnetic poles.
None of the choices because magnetic poles does'nt deal with charges instead it deals with poles
47
The ability of a magnetic material to concentrate magnetic flux.
Permeability
48
Which of the following is the permeability of free space?
1.26x10^-6 H/m
49
Diamagnetic materials has relative permeability:
less than 1
50
Materials which act like magnets when subjected to a magnetic field.
Paramagnetic
51
Which is true about ferromagnetic materials?
u_r >>1
52
The force that tends to push out the magnetic flux in a magnetic circuit.
Magnetomotive force (MMF)
53
1AT is equal to:
1.26 Gilberts (Gb)
54
Magnetic field strength is represented by:
H
55
Oersted is equivalent to:
Gb/cm (Gilberts per centimeter)
56
1Wb is equal to:
1x10^8 lines
57
The number of magnetic lines of force per unit area of a section perpendicular to the direction of flux.
Magnetic flux density (B)
58
Which of the following is a unit of Flux density?
Tesla (T)
59
What is the Law for Electromagnetic Induction?
Faraday's Law
60
States that when a conductor cuts a magnetic flux, the conductor induces its own EMF
1st Law of Faraday
61
Electromagnets are types of magnets made by:
conductor coil with current
62
The totality of magnetic lines of force going out from a magnet.
Magnetic Flux
63
The amount of induced EMF in a coil cutting a magnetic flux is directly proportional to the rate at which the flux is being cut. This is described by:
2nd Law of Faraday
64
The induced EMF is directly proportional to:
number of coil turns
65
Flux rate can be expressed as:
both Wb/s and Mx/s
66
The law that determines the polarity of the induced voltage.
Lenz's Law
67
In the left hand rule for coils, the thumb points to:
The direction of north pole
68
In the left hand rule for current carrying conductors, the thumb points to:
the direction of current
69
In the left hand rule for generators, the thumb points to:
the direction of cutting
70
Lenz's law states that, the magnetic field of the induced current must oppose the:
magnetic field of the flux being cut
71
If a neutral atom loses one of its valence electrons, it becomes a(n)
Both Electrically charged atom and Positive ion
72
Aluminum, with an atomic number of 13, has
Both 3 valence electrons and 13 protons in its nucleus
73
The atomic number of an element is determined by:
The number of protons.
74
In a compound:
There must always be two or more elements.
75
In a metal conductor, such as a copper wire,
Free electrons are the moving charges that provide current
76
Of the following substances, the worst conductor is:
Air
77
If a material has low resistance:
It is a good conductor.
78
Which of the following statements is true?
Both Like charge repel each other and Unlike charge attract each other
79
Which of the following statements is true?
Voltage can exist without current
80
One ampere of current corresponds to
1C/1s
81
What is the output voltage of a battery expends 12J of energy in moving 1.5C of charge?
8V
82
The current which flows when 0.1 coulomb is transferred in 10ms is:
10A
83
A stroke of lightning:
Is a discharge of static electricity
84
In some batteries, chemical energy can be replenished by:
Charging it
85
A positive electric pole:
Has a fewer electrons than the negative pole.
86
The total flux in the core of an electrical machine is 20mWb and its flux density is 1T, The cross-sectional area of the core is:
0.02m^2
87
A coil of 100 turns is wound uniformly on a wooden ring. The ring has a mean circumference of 1m and a uniform cross-sectional area of 10 cm^2. The current in the coil is 1A. The magnetic field strength is:
100 A/m
88
Which of the following statements is false?
The remanence of a ferrous material is measured in ampere/meter
89
Two bar magnets are placed parallelto each other and about 2 cm apart, suct that the south pole of one magnet is adjacent to the north pole of the other. With this arrangement, the magnets will:
Attract each other
90
The tesla (T) is a unit of
flux density
91
A commercial permanent magnet will last indefinitely if it is not subjected to
a strong demagnetizing field, physical shock, and high temperatures
92
If the north (N) pole of a permanent magnet is placed near a piece of soft iron, what is the polarity of the nearest induced pole?
South (S) pole
93
A material that becomes strongly magnetized in the same direction as the magnetizing field is classified as
ferromagnetic
94
1 uWb (MicroWeber) equals
100 Mx (Maxwells)
95
When a small voltage is generated across the width of a conductor carrying current in an external magnetic field, the effect is called
The HALL Effect
96
With an electromagnet,
Both more current and more coil turns mean a stronger magnetic field and if there is no current in the coil, there is no magnetic field
97
When a magnetic flux of 10Wb links with a circuit of 20 turns in 2s, the induced e.m.f. is:
100V
98
A conductor carries a current of 10A at right-angles to a magnetic field having a flux density of 500 mT. If the length of the conductor in the field is 20cm, the force on the conductor is:
1N
99
An electric bell depends for its action on:
an electromagnet
100
The magnetic field due to a current-carrying conductor takes the form of:
concentric circles
101
Which of these can represent magnetomotive force?
The ampere-turn.
102
A coil has 500 turns and carries 75 mA of current. The magnetomotive force will be:
37.5 At
103
The change in the direction of a compass needle, when a current-carrying wire is brought near, is:
Electromagnetic deflection
104
Geomagnetic lines of flux:
Are horizontal at the geomagnetic equator
105
The force between a magnet and a piece of ferromagnetic metal that has not been magnetized:
Is never repulsive.
106
A unit of overall magnetic field quantity is the:
Maxwell
107
An advantage of an electromagnet over a permanent magnet is that:
An electromagnet can be switched on and off.
108
A relay is connected into a circuit so that a device gets a signal only when the relay coil carries a current. The relay is probably:
Normally open
109
A high tape-rcorder motor speed is generally used for:
Video
110
An advantage of a magnetic disk, as compared with magnetic tape, for data storage and retrieval is that:
Data can be stored and retreived more quickly with disks than with tapes.
111
For the current-carrying conductor lying in the magnetic field shown in figure (a) below, the direction of the force on the conductor is: (use conventional current flow and dot means current is towards you)
upwards
112
For the current-carrying conductor lying in the magnetic field shown in figure (b), the direction of the cureent in the conductor is: :(use conventional current flow and dot means current is towards you)
towards the viewer
113
Suppose a certain current in a galvanometer causes the needle to deflect 20 degrees, and then this current is doubled. The needle deflection:
will increase
114
Lines of magnetic flux are said to originate:
At a north magnetic pole
115
If a conductor is horizontal, the current flowing from left to right and the direction of the surrounding magnetic field is from above to below, the force exerted on the conductor is: :(use conventional current flow)
away from the viewer
116
A bar magnet is moved at a steady speed of 1.0 m/s towards a coil of wire which is connected to a center-zero galvanometer. The magnet is now withdrawn along the same path at 0.5 m/s. The deflection of the galvanometer is in the:
opposite direction as previously, with the magnitude of the deflection halved.
117
The point at which a magnetic material loses its ferrromagnetic properties is called the
Curie temperature
118
The flux density in the iron-core of an electromagnet is 0.25 T. When the iron-core is removed, the flux density drops to 62.5 x 10^-6 T. What is the relative permeability of the iron core?
ur= 4000
119
The flux density in the iron-core of an electromagnet is 0.25 T. When the iron-core is removed, the flux density drops to 62.5 x 10^-6 T. What is the relative permeability of the iron core?
ur = 4000
120
The force on an electron travelling at 10^7 m/s in a magnetic field of density 10uT is 1.6 x 10^-17N. The electron has a charge of:
1.6 x 10^-19C
