# Introduction to electricity - practice problems

```Chapter1
Lesson 1
Electric current intensity
Use the following constants if needed: ( e = 1.6 X 10-19 C )
1. If an electric current often density 5A passes through a conductor, the
quantity of electric charges that passes through a certain cross-section of
the conductor within 2 seconds equals……
a) 2.5 C
b) 5 C
c) 10 C
d) 20 C
2. The electric current that passes in conductor equals 0.3 A, which means… …
a) The quantity of electric charge that is contained in the conductor is 0.3 C.
b) The quantity of electric charge that passes through a cross-section of the
conductor in 1 S is 0.3 C.
c) The time interval in which a unit charge passes through a cross-section of
the conductor is 0.3 S.
d) The rate of which the electric charges pass through a cross-section of the
conductor is 0.3 C per minute.
3. Which of the following electric circuits shows the conventional direction of
current (I) and the direction of the free electrons motion (e-) correctly?
4. The opposite diagram shows a section of a conductor that carries an electric
current, so which of the following choices shows the relation among current
antennas at the cross sections X, Y and Z?
a) Ix &gt; Iy &gt; Iz
b) Ix = Iy = Iz
c) Ix &lt; Iy &gt; Iz
d) Ix &lt; Iy &lt; Iz
5. The opposite graph represents the relation between the quantity of a
charge (Q) that flows through a cross-section of a conductor in a DC (direct
current) circuit and the time (T), so the intensity of the current is… … ..
a) 2 A.
b) 10 A.
c) 50 A.
d) 250 A.
6. An electric current of antennas 5 mA passes through a wire, so:
(1) the electric charge that passes through a definite cross-section of the
wire in 10 s equals……….
a) 5 x 10-4 C.
b) 0.05 C.
c) 5 C.
d) 2000 C.
(2) The number of electrons that pass through that cross section in the
same time interval is… …
(take: e= 1.6 x 10-19 C)
a) 3.125 x 1017 electrons.
b) 1.25 x 1022 electrons.
c) 8.379 x 1018 electrons.
d) 3.125 x 1019 electrons.
7. The opposite graph represents the relation between the
number of electrons (N) that pass through a certain crosssection of a conductor in an electric circuit and the time (T),
so the graph that represents the relation between the
current and tensity (I) that passes through this conductor
and the time (T) is…
Electric potential difference
8. The potential difference between two points when a work done of 30 J is
required to transfer an electric charge of 10 C between them equals…
a) 0.3 V.
b) 3 V.
c) 30 V.
d) 300 V.
9. The opposite diagram represents a part of an electric circuit containing
device X and the device Y, so if the reading of each equals one unit on its
scale, so…
a)
b)
c)
d)
Device X
Ammeter
Milliammeter
Ammeter
Milliammeter
Device Y
Voltmeter
Voltmeter
Millivoltmeter
Millivoltmeter
10. Coulomb is the amount of electric charge ……………
a) That when passed through a cross-section of a conductor in 5 S, it means
that a current of 50 A has flowed through the conductor.
b) That when passed through a cross-section of a conductor in 50 S, it
means that a current of 0.5 A has flowed through the conductor.
c) Which needs a work done of 5 J to be transferred between two points of
potential difference 0.5 V
d) Which needs a work done of 0.05 J to be transferred between two
points of potential difference 0.05 V
11. Which of the following graphs represents the relation between the
potential difference (V) across the terminals of a conductor that carries a
direct current (DC) and the time (T)?
12. The opposite circuit contains two devices X and Y that are connected
correctly, so which of the following choices represents the measuring unit
of the quantity that measured by device X and the measuring unit of the
quantity that is measured by device Y?
a)
b)
c)
d)
Device X
Coulomb/second
Coulomb/second
Joule/coulomb
Joule/coulomb
Device Y
Volt
Ampere
Volt
Ampere
13. If the work done to transfer a quantity of electric charge of 5 C each 1 S
between two points in a conductor is 100 J, then:
(1) The potential between the two points equals……..
a) 0.05 V.
b) 5 V.
c) 10 V.
d) 20 V.
(2) The flowing electric current intensity through the conductor
equals…….
a) 2.5 A.
b) 5 A.
c) 7 A.
d) 12 A.
(3) The number of electrons that pass between the two points through
2 S equals……….
( where: e = 1.6 x 10-19 C )
a) 4.22 x 1018 electrons.
b) 1.56 x 1019 electrons.
c) 6.25 x 1019 electrons.
d) 1.25 x 1019 electrons.
14. In which of the following cases the arrow represents the correct direction
of the electric current through the resistance between the two points A, B?
Electric resistance and Ohm’s law
15. In which of the following cases the intensity of the current that passes in
resistor R is greater than others?
16. Each of the following diagrams represents a part of an circuit, then in which
of them the ammeter and the voltmeter are correctly connected such that
the resistance of resistor R can be determined using their readings?
17. A potential difference of 12 V is applied between the terminals of a
conductor to move 6.25 x 1018 electrons through a cross-section of this
conductor within two seconds, then the resistance of the conductor is ………
( take: e = 1.6 x 10-19 C )
a) 24 Ω.
b) 12 Ω.
c) 6 Ω.
d) 3.84 Ω.
18. An electric bulb of resistance 1.6 Ω is connected to a 9 V battery, so the number
of electrons that passes through a cross-section of the bulb’s filament every
minute equals …………….
( where: e = 1.6 x 10-19 C )
a) 2.6 x 1019 electrons.
b) 2.9 x 1019 electrons.
c) 2.4 x 1020 electrons.
d) 2.1 x 1021 electrons.
19. A conductor of resistance 10 Ω carries an electric current of intensity 0.5 A. if
an electric current of intensity 1 A passes through the same conductor at
constant temperature, then its resistance equals ………
a) 2.5 Ω.
b) 5 Ω.
c) 10 Ω.
d) 20 Ω.
20. The opposite graph represents the relation between the
potential difference across each of two wires A, B separately and
the current intensity that is passing in each of them, then which
of the two wires has a higher resistance and why?
a)
The wire of the
higher resistance
A
b)
A
c)
B
d)
B
The reason
Because the slop of the line represents the resisitance of the
wire
Because the reciprocal of the slope of the line represents te
resistance of the wire
Because the slop of the line represents the resisitance of the
wire
Because the reciprocal of the slope of the line represents te
resistance of the wire
21. In the opposite electric circuit, what is the factor that should be increased
in order to increase the current intensity through the circuit?
a) The electromotive force of the battery.
b) The length of the connecting wires.
c) The resistance which is taken from R.
d) The temperature of the resistance R.
22. In the opposite circuit, which of the following graphs
represents the relation between:
(1) The reading of the ammeter and the value of the
resistance which is taken from Rv?
(2) The reading of the voltmeter and the value of the resistance which
is taken from Rv?
(3) The reading of the ammeter and the voltmeter when the value of
the resistance which is taken from Rv changes?
Electric power and electric energy
23. Which of the following units isn’t equivalent to watt?
a) J/S.
b) A.V.
c) A2.Ω.
d) Ω2.V.
24. The opposite graph represents the relation between the consumed power
in a conductor and the square of the intensity of the electric current that
passes through it, so the resistance of the conductor equals…….
a) 2 Ω.
b) 5 Ω.
c) 50 Ω.
d) 0.5 Ω.
25. Which of the following graphs represents the relation between the
consumed power (Pw) in a conductor that carries a direct current (DC) and
time (T)?
26. Which of the following graphs represents the relation between the
consumed energy (W) in a conductor that carries a direct current (DC) and
time (T)?
27. For the opposite circuit, which of the following graphs represents
the relation between the consumed power through a resistance Rv
and its value?
28. An electric fan is labelled with (220 V – 100 W) and an electric heater is
labelled with (220 V – 1000 W), then the resistance of the heater is ………..
that of the fan.
a) Equal to.
b) Less than.
c) Larger than.
d) Indeterminable with respect to.
29. Two wires are made of conducting metals, if 1020 electron pass through a
cross-section of the first wire that has resistance R every second and 2 x 1020
electrons pass through a cross-section of the second wire every second wire
which has a resistance 2 R, so the ratio between the consumed power in the
first wire to that in the second wire equals………..
7
1
a)
b) 3
c) 8
d)
3
8
7
The factors on which the electric
resistance depends
30. The resistivity of copper = 1.8 x 10-8 Ω.m, which means that………….
a) The resistance of copper wire that is 1 m long and has a 1 m diameter
equals 1.8 x 10-8 Ω.
b) The resistance of copper wire that is 0.5 m long and has a 0.5 m2 crosssectional area equals 1.8 x 10-8 Ω.
c) The resistance of a unit length of copper equals 1.8 x 10-8 Ω/m.
d) The resistance of a unit volume of copper equals 1.8 x 10-8 Ω/m3.
31. Which of the following graphs represents the variation of resistance (R) of
several copper wires that have the same length versus cross-sectional area
(A)?
32. Which of the following graphs represents the variation of resistivity (ρe) for
a group of wires of different materials versus conductivity (σ)?
33. Which of the following figures represents the relation between the
conductivity (σ) of the material of conductor and its cross-sectional area (A)?
34. Which of the following choices describes what happens to the resistance
of a conductor when increasing its cross-sectional area and why?
a)
The conductor
resistance
Increases
b)
Increases
c)
Decreases
d)
Decreases
The reason
Because increasing the cross-sectional area is considered as
Because increasing the cross-sectional area is considered as
Because increasing the cross-sectional area is considered as
Because increasing the cross-sectional area is considered as
35. If the length of a copper wire is doubled and its cross-sectional are is
decreased to its half, then its resistance………….
a) doubles.
b) Decreases to its half.
d) Decreases to its quarter.
36. A conductor of regular cross-section whose length is 20 m has a resistance
of 180 Ω, so if another conductor of the same material has a length of 5 m
while its cross-sectional area is three times as large as that of the first
conductor, then the resistance of the second conductor equals…………
a) 81 Ω.
b) 27 Ω.
c) 9 Ω.
d) 6 Ω.
37. If three copper wires X, Y and Z have length of 2 m, 4 m and 1 m respectively
while having the same cross-sectional area, then which of the following
graphs represents the ratios of the resistances of the three wires?
38. The opposite table shows
different value of lengths,
cross-sectional area and
resistivities for wires that
materials, so which of these
wires:
1)
2)
3)
4)
Wire length
L (m)
Cross-sectional
area A (cm2)
Resistaitvity
ρe x 10-4 (Ω.m)
10
5
5
0.5
0.1
0.5
0.1
0.5
0.05
0.25
0.5
0.005
(1) Carries a current of intensity 2 A passes when the potential
difference between its terminal equals 10 V?
a) Wire (1).
b) Wire (2).
c) Wire (3).
d) Wire (4).
(2) Gives larger amount of heat than the other wires when the same
current intensity passes in them for the same time interval?
a) Wire (1).
b) Wire (2).
c) Wire (3).
d) Wire (4).
(3) Gives less thermal power than the other wires when each of them
is connected between the same potential difference?
a) Wire (1).
b) Wire (2).
c) Wire (3).
d) Wire (4).
39. A wire of iron which is 3.14 m long and has a radius of 0.5 mm is connected
between the terminals of a 5 V battery. If the resistivity of the iron is 10-7
Ω.m, so the passing electric current intensity in the wire equals………………
(take: π=3.14)
a) 6.2 A.
b) 8.2 A.
c) 9.6 A.
d) 12.5 A.
40. The opposite figure represents an incomplete electric circuit, if you have
four wires of the same material but different in both length and thickness,
each of them is connected separately between the two points (X,Y), then
the ammeter reading becomes maximum when the connected wire is
the…………………..
a) Longest and thickest.
b) Longest and thinnest.
c) Shortest and thickest.
d) Shortest and thinnest.
41. He opposite figure represents the length and cross-sectional areas of four
wires which are made of the same material. So, at the same temperature if
each of them is connected between the same electric potential difference,
the correct order of the wires according to the passing electric current
intensity in each of them is ………………………
a) c &gt; b = d &gt; a.
b) a &gt; b = d &gt; c.
c) b &gt; a = c &gt; d.
d) d &gt; a = c &gt; b.
42. In the opposite electric circuit, when the position of the slider is changed
from position A position B, which of the following choices represents what
happens in the circuit?
The length of the rheostat wire
that carries an electric current
The intensity of the current that
passes in the circuit
Increases
Increases
Decreases
Decreases
Increases
Decreases
Increases
Decreases
a)
b)
c)
d)
43. If the resistivity of copper is 1.8 x 10-8 Ω.m, then which of the following
wires represents a copper wire of a cross-sectional area 10 mm2?
a)
b)
c)
d)
Its length
10 m
10 m
1m
1m
Its resistance
1.8 x 10-8 Ω
0.018 Ω
1.8 x 10-4 Ω
1.8 Ω
44. A wire of length 200 m has resistivity of 3.14&times;10-7 Ω.m, if the wire allows
the flow of 2x1019 electrons per second when it is connected to source of
64V, the radius of the wire equals……………. (take: π = 3.14)
a) 10-1 m.
b) 10-2 m.
c) 10-3 m.
d) 10-4 m.
45. Two wires are of the same material, the length of the second wire equals
double the length of the first wire and its diameter equals the radius of first
wire, so the ratio between the resistance of the second wire and that of the
first wire equals………….
1
8
b) 8.
1
c)
2
d) 2.
a)
46. Two wires are made of copper, the length of the first wire is 10m and it's
mass is 0.1 kg, while those of the other wire are 40 m and 0.2 kg,
respectively, so the ratio between their resistance equals…….…
1
a) 4
1
b)
5
1
c)
7
1
d)
8
47. The opposite figure shows a conducting soiled cuboid where each two
opposite faces of the cuboid can be connected between the terminals of an
electric source and the paths (1), (2) and (3) are the probable pathways
electric currents through the conductor, so in which of these paths the
electric current faces the highest resistance?
a) Path (1).
b) Path (2).
c) Path (3).
d) All paths have the same resistance.
48. When's the length of a conductor has doubled and its cross-sectional area
has decreased to half its original value, then the resistivity of its
material……………
b) Is tripled.
c) Gets halved.
d) Remains unchanged.
49. A wire is 106.3 cm long whose cross-sectional area is 1 mm2 and it's
resistance is 1 Ω, so:
(1) The resistivity of the wire's material equals…………..
a) 9.41 x 10-7 Ω.m.
b) 8.53 x 10-7 Ω.m.
c) 5.71 x 10-6 Ω.m.
d) 6.25 x 10-6 Ω.m.
(2) The conductivity of the wire's material equals…………
a) 1.89 x 106 Ω-1.m-1.
b) 2.35 x 109 Ω-1.m-1.
c) 7.35 x 108 Ω-1.m-1.
d) 1.06 x 106 Ω-1.m-1.
50. Two wires (X) and (Y) that are made of different materials have the same
resistance where the length of wire (X) of double that of wire (Y) and the
radius of wire (X) is double that of wire (Y), so the ratio between the
resistivities of their materials equals…………….
a)
c)
1
4
1
2
b)
d)
1
3
2
1
51. When the length of a metallic wire decreases to its half and its radius
increases to its double, the conductivity of its material………….
a) Increases to the double.
b) Decreases to the half.
c) Remains unchanged.
52. The opposite graph represents the relation between the resistance (R) of a
wire and its length (L). if the cross-sectional area of the wire is 0.1 cm2, so:
(1) The resistivity of the wire’s material (ρe) equals………….
a) 3 x 10-7 Ω.m.
b) 5 x 10-6 Ω.m.
c) 4 x 10-5 Ω.m.
d) 9 x 10-8 Ω.m.
(2) The resistance of a 25 m long section of this wire equals………….
a) 9.25 Ω.
b) 11.3 Ω.
c) 12.5 Ω.
d) 15.9 Ω.
53. The opposite graph represents the
variation of resistance (R) for several wires
with the reciprocal of the cross-sectional
1
area ( ). If the wires are made of the same
A
material and the length of each of them is 12
m, so:
(1) The conductivity of the wire’s material
equals…………..
a) 2 x 105 Ω-1.m-1.
b) 3 x 107 Ω-1.m-1.
c) 4 x 106 Ω-1.m-1.
d) 8 x 109 Ω-1.m-1.
(2) The resistance os a wire of the same material that has the same length
as these wires but of cross-section area 0.0025 cm2 equals………
a) 10 Ω.
b) 11 Ω.
c) 12 Ω.
d) 15 Ω.
54. A wire of length 30 m and cross-sectional area 0.3 cm2 is connected to a DC
source and an ammeter of negligible resistance in a closed circuit, if an
electric current of intensity 2 A passes through the wire when the potential
difference between its terminals is 0.8 V, so the conductivity of the wire
equals………………
a) 19 x 106 Ω-1.m-1.
b) 25 x 105 Ω-1.m-1.
c) 17 x 108 Ω-1.m-1.
d) 23 x 109 Ω-1.m-1.
55. A metal insulated wire of diameter 0.1 mm is made of an alloy, the
resistivity of its material is 5 x 10-7 Ω.m, so the electric conductivity of the
material of that wire and the required length of that wire for obtaining a
resistance of 200 Ω respectively are……….. (take: π = 3.14)
a) 8.13 m, 3 x 107 Ω-1.m-1.
b) 5.13 m, 2 x 106 Ω-1.m-1.
c) 2.19 m, 3 x 107 Ω-1.m-1.
d) 3.14 m, 2 x 106 Ω-1.m-1.
56. The opposite graph represents the variation of the potential difference (V)
between the ends of a wire of length 5 m and cross-sectional area 0.1 mm2
versus the current intensity (I) through the wire, so the conductivity of the
wire’s material equals………
a) 4.1 x 106 Ω-1.m-1.
b) 3.2 x 105 Ω-1.m-1.
c) 2.5 x 106 Ω-1.m-1.
d) 1.6 x 105 Ω-1.m-1.
57. The opposite graph represents the variation of resistance (R) with length
(L) for two copper wires (X) and (Y), so the ration between the crosssectional area of the two wires ( Ax ) is ………………
Ay
a)
c)
1
3
3
1
b)
d)
1
2
√3
1
58. A metallic rod in the shape of a cylinder of cross-sectional area 2 cm2 and
resistance 22.5 Ω is pulled uniformly until its cross-sectional area become
1.5 cm2, so its resistance will be……………
a) 37 Ω.
b) 40 Ω.
c) 52 Ω.
d) 56 Ω.
59. If a metallic wire was drawn regularly until its length has increased to the
duble, then its resistance is ……………..its original value.
a) Doubled.
b) Halved.
d) Quartered.
60. The opposite graph shows the variation of the
electric potential difference with the electric
current intensity in the two wires of the same
material, so:
(1) The cross-sectional area of wire A, if both
wires have the same length and the crosssectional area of wire B is 3 x 10-6 m2,
equals…………
a) 10-6 m2.
b) 9 x 10-6 m2.
c) 3 x 10-6 m2.
d) 12 x 10-8 m2.
(2) The length of wire A, if both have the same cross-sectional area and
the length of wire Bis 3m, equals…………….
a) 1 m.
b) 2 m.
c) 3 m.
d) 9 m.
61. A conductor of length (L) and cross-sectional area A is made of material
of electric conductivity (σ), if a potential difference (V) is applied between
its terminals, a quantity of electric charge (Q) passes through a cross-section
of the conductor within a time interval (T), so which of the following
mathematical relation is correct for this conductor?
σV
V
a) Q =
b) Q = ALT
σALT
σVT
σVAT
c) Q =
d) Q =
AL
L
62. Two wire are of the same length and the same resistance but one of them
is made of copper and the other is made of iron, so the ratio between their
RCu
a)
(ρe)Fe
(ρe)Cu
b)
(ρe)Fe
√(ρe)Cu
c)
√(ρe)Fe
(ρe)Cu
d)
√(ρe)Fe
√(ρe)Cu
63. The opposite diagram shows a section of a conductor whose resistivity is
ρe. if the cross-sectional areas of its two terminals are different, the value of
its resistance is………………
ρeL
A
ρeL
c) Less than
A
a) Equal to
b) Greater than
d) Equal to
ρeL
A
ρeL
2A
64. A power station is connected to a factory 2.5 km away by two wires. If the
potential difference at the station is 240 V and at the factory is 220 V and
the factory is using a current of 80 A, so
(1) The resistance of one meter of the wire equals…………
a) 5 x 10-5 Ω/m.
b) 6 x 10-5 Ω/m.
c) 12 x 10-5 Ω/m.
d) 1 x 10-4 Ω/m.
(2) The radius of the wire if the resistivity of its material is 1.57 x 10-5 Ωm
a) 0.007 m.
b) 0.004 m.
c) 0.05 m.
d) 0.01 m.
65. A solid cube which is made of a conducting material of side length 10 cm is
reshaped to be a cylindrical wire of electric resistance 20Ω, if the resistivity
of the material of the cube is 10-7 Ω.m, so the length of the wire equals
……….. (take: π = 3.14)
a) 340.75 m.
b) 447.21 m.
c) 656.41 m.
d) 523.32 m.
66. A wire of length 2 m is made of material of density 7000 kg/m3, if it has
resistance of 2 Ω and a resistivity of 10-6 Ω.m, so it mass equals………………
a) 0.012 kg.
b) 0.014 kg.
c) 0.016 kg.
d) 0.018 kg.
67. A metal wire of volume 2 x 10-4 m3 and cross-sectional area 4 x 10-5 m2 has
a resistance of 1.25 Ω, so its conductivity equals……………..
a) 103 Ω-1.m-1.
b) 105 Ω-1.m-1.
c) 108 Ω-1.m-1.
d) 107 Ω-1.m-1.
68. The opposite graph represents the variation
of the potential difference (V) across two
wires (X and Y) that have the same length with
the current intensity (I) in both of them at
constant temperature.
If the ratio between the cross-sectional areas
Ax
12
of the two wires (
) equals (
), so the
Ay
25
ratio between the resistivity of their materials
(ρe)x
(
) equals………….
(ρe)y
a)
2
1
b)
1
1
c)
1
4
d)
1
7
69. A wire of length 2 m has across-sectional area of 4 x 10-6 m2 when the
potential difference between the terminal of the wire was 20 V, the
consumed power through the wire was 10 W, so:
(1) The resistivity of the wire’s material equals………………
a) 2 x 10-7 Ω.m.
b) 10-5 Ω.m.
c) 8 x 10-5 Ω.m.
d) 4 x 10-6 Ω.m.
(2) The number of electrons that passthrough a cross-section of the wire
in one minute equals………….
a) 9.741 x 1017 Electrons.
b) 6.435 x 1018 Electrons.
c) 2.314 x 1019 Electrons.
d) 1.875 x 1020 Electrons.
70. Electric bulb A of power 80 W which works on a potential difference of 220
V is used in house lighting and another electric bulb B of power 20 W which
work on a potential difference of 24 V is used in cars, if the filaments of the
two bulbs are made of the same material and have the same length, so the
ratio between the radii of the two filaments ( rA ) equals ……………….
rB
a)
6
55
b)
12
55
c)
24
55
d)
96
55