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Revision Electrisity part 1
الأربعاء 11 فبراير 2015, 21:07
Revision Electrisity part 1
FIRST; Definitions 0f the basic concepts
A- Questions in this part are dealing with the basic concepts. The student has to write the scientific meaning corresponding to the concept in each case.
1- The work done in joule to transfer unit charge (one coulomb) between two points.
The potential difference between two points
2- The voltage difference between the two terminals of the cell when no current passes through the circuit(the current vanishes)
The e.m.f of the source
3- The potential deference across the two terminals of a conductor carries current of intensity one ampere.
The resistance of conductor.
4- The current intensity flowing through a conductor is directly proportional to the potential difference across its terminals, at constant temperature.
Ohm’s law
5- The resistance of a wire 1 m long whose cross sectional area 1 m2.
Resistivety of the conducting material
6- The reciprocal of the resistivety of the conducting material.
Electrical conductivity
7- The potential difference across the combination of resistors must be equal to the sum of the potential difference across each resistor.
Kirchhoff’s law
8- The potential difference between two points when work equals 1J is done to transfer a quantity of charge 1 coulomb between them.
The volt (S.I unit of pot.diff.)
9- The resistance of a conductor that supports a current of 1A when the voltage difference between its terminals equals 1volt.
Ohm(SI unit of resistance)
10- The current intensity when a quantity of charge 1columb pass
through a given cross-sectional of a circuit in one sec.
Ampere (SI unit of current intensity)
B-What is meant by
1- The copper resistivety =1.8 x 10-8Ωm. ……………………….
The resistance of a copper wire 1 m long whose cross sectional area 1 m2=1.8 x 10-8Ω
2- The electric conductivity of a material 4 Ω-1m-1.
The reciprocal of the resistivety of the wire made from copper =4 Ω-1m-1
3-The voltage difference between two points =20 volt………….
The work done in joule to transfer a charge of one coulomb between two points. =20 j
4-The electromotive force of an electric cell =1.5 Volt ………….
The total wok done to transfer unit charge throughout the electric circuit inside and outside the cell = 1.5 j
5-The work done to transfer an electric charge of 8 coulomb in an electric circuit between two points = 64 joule. ………………
The potential difference across the two terminals of a conductor carries current of intensity one ampere = 10 volt
Second; Choose the correct answer from those between brackets and write it in your answer paper:
In the electrical circuit illustrated in the figure, the reading of the ammeters A1,A2 respectively are……
a-4A, 2A b – 1A, 4A, c- 4A ,3A
If the E.M.F of a cell equals 8 volt, its terminal voltage when a current is flowing through its circuit equals … a-8 volt b– less than 8 c– greater than 8 volt
.
If the E.M.F of a cell equals 1.5 volt, its terminal voltage when no current is flowing through its circuit equals …
a-1.5 volt b– less than c–greater than 1.5
Two resistors. are connected in parallel. One of them equals 1 ohm. Their equivalent resistance is
a-greater than1Ω b – equal to1Ω c- smaller than 1Ω.
Two resistors are connected in a circuit as shown. the total resistance of the resistors is
a-less than 2W. b-between 2W and 3W. c- less than 3W .
The unit equivalent to Coulomb / second is:
a-Volt b – Ampere c- Ohm d- Farad]
.
In the electric circuit shown in the figure, if the reading of the ammeter (A1) was 1.2 ampere then the reading of the ammeter (A2) equal
….
( a-0.8A 0.4A c-1.2A)
.
8-In the electric circuit shown in the figure. If the reading of the ammeter(A) is 5 ampere and the current passing through the resistance R1, is 2 ampere then the value of the resistance R2, Is.—–
a-4W. b- 3W. c- 6W .
9-Four lamps 6W each are connected in parallel. The combination is connected to a 12V battery with a negligible internal resistance: The total resistance of the lamps equals……………
a)2/3W b) 24W c)3/2W d) 12W
10-Using the same data given in the previous question The current in each lamp is…………………………………
a) 3/2A b) 2A c) 2/3
11-When the circuit shown is connected, the 6V lamp glows. What happens to the brightness of the lamp when switch S is closed?
a-it becomes dimmer. b-it becomes brighter.
c-it goes off. d-it remains the same
In the circuit shown in the figure the switch S is open. When the switch is closed the reading of the ammeter changes from
0.5A to 1A b- 1A to 0.5A c- 1A to 2A
A cylindrical piece of a soft electrically-conducting material has resistance R. it is rolled out so that its length is doubled but its volume stays constant.
What is its new resistance?
a b-R c-2R d-4R
lf the length of a resistor is doubled and its cross-sectional area is decreased to one half, then its resistance becomes
a-Double its value b-4 times its value c-fixed
In which circuit from (a) to (e) will the current in R1 be different from that in R2?
D
In which circuit (a) to (e) is the effective resistance smallest?
D
In which circuit will the voltage across R1 be smaller than the resistance R2?
A
18-In the opposite fig the reading of ammeter is …..ampere
a-3/4 b-2 c1/2
Third; Important Give Reasons :
When no current passing through the electrical circuit the electromotive force of a battery equals the potential difference between its terminals.
Since the electromotive force of a battery is given by (VB= V+Ir ) therefore when no current passes through the circuit (the key is switched off ) the term Ir = 0 . Hence the potential difference between its terminals becomes equal to the electromotive force.
The electric conductivity of a conductor is considered as physical property to the material of such conductor ……
Because it depends on the type of the material and differ from one material to other at the same temperature.
Work must be done to transfer electric charges from one point to another.
Due to the existence of the potential difference between them .
Efficiency of the battery increases by the decrease of its internal resistance.
As , the efficiency of the battery is given by( V/V_B ×100=R/(R+r)×100) For that , when the internal resistance of the battery decrease the efficiency of the battery increase also, the lost of the work done (wasted energy) is reduced during operation.
In electric circuits connected in parallel, thick wires are used at the ends of the battery, but at the ends of each resistor less thick wires are used.
Because the current intensity in parallel circuits is greater at the input and output compared to the current in each branch.
The electrical conductivity of copper is high.
As the resistivity of copper is small
Connection of electrical devices in home in parallel. or The home electric devices are not connected in series.
In order to maintain the potential difference constant and increase the intensity of current across the devices. also, if a device is cut off, the other still operate.
Fourth; important Comparisons
The electrical conductivity and the resistivity from the point of view the definition of each , write the mathematical relation & the units.
Resistance and resistivity from the point of view the unit of each .
FIRST; Definitions 0f the basic concepts
A- Questions in this part are dealing with the basic concepts. The student has to write the scientific meaning corresponding to the concept in each case.
1- The work done in joule to transfer unit charge (one coulomb) between two points.
The potential difference between two points
2- The voltage difference between the two terminals of the cell when no current passes through the circuit(the current vanishes)
The e.m.f of the source
3- The potential deference across the two terminals of a conductor carries current of intensity one ampere.
The resistance of conductor.
4- The current intensity flowing through a conductor is directly proportional to the potential difference across its terminals, at constant temperature.
Ohm’s law
5- The resistance of a wire 1 m long whose cross sectional area 1 m2.
Resistivety of the conducting material
6- The reciprocal of the resistivety of the conducting material.
Electrical conductivity
7- The potential difference across the combination of resistors must be equal to the sum of the potential difference across each resistor.
Kirchhoff’s law
8- The potential difference between two points when work equals 1J is done to transfer a quantity of charge 1 coulomb between them.
The volt (S.I unit of pot.diff.)
9- The resistance of a conductor that supports a current of 1A when the voltage difference between its terminals equals 1volt.
Ohm(SI unit of resistance)
10- The current intensity when a quantity of charge 1columb pass
through a given cross-sectional of a circuit in one sec.
Ampere (SI unit of current intensity)
B-What is meant by
1- The copper resistivety =1.8 x 10-8Ωm. ……………………….
The resistance of a copper wire 1 m long whose cross sectional area 1 m2=1.8 x 10-8Ω
2- The electric conductivity of a material 4 Ω-1m-1.
The reciprocal of the resistivety of the wire made from copper =4 Ω-1m-1
3-The voltage difference between two points =20 volt………….
The work done in joule to transfer a charge of one coulomb between two points. =20 j
4-The electromotive force of an electric cell =1.5 Volt ………….
The total wok done to transfer unit charge throughout the electric circuit inside and outside the cell = 1.5 j
5-The work done to transfer an electric charge of 8 coulomb in an electric circuit between two points = 64 joule. ………………
The potential difference across the two terminals of a conductor carries current of intensity one ampere = 10 volt
Second; Choose the correct answer from those between brackets and write it in your answer paper:
In the electrical circuit illustrated in the figure, the reading of the ammeters A1,A2 respectively are……
a-4A, 2A b – 1A, 4A, c- 4A ,3A
If the E.M.F of a cell equals 8 volt, its terminal voltage when a current is flowing through its circuit equals … a-8 volt b– less than 8 c– greater than 8 volt
.
If the E.M.F of a cell equals 1.5 volt, its terminal voltage when no current is flowing through its circuit equals …
a-1.5 volt b– less than c–greater than 1.5
Two resistors. are connected in parallel. One of them equals 1 ohm. Their equivalent resistance is
a-greater than1Ω b – equal to1Ω c- smaller than 1Ω.
Two resistors are connected in a circuit as shown. the total resistance of the resistors is
a-less than 2W. b-between 2W and 3W. c- less than 3W .
The unit equivalent to Coulomb / second is:
a-Volt b – Ampere c- Ohm d- Farad]
.
In the electric circuit shown in the figure, if the reading of the ammeter (A1) was 1.2 ampere then the reading of the ammeter (A2) equal
….
( a-0.8A 0.4A c-1.2A)
.
8-In the electric circuit shown in the figure. If the reading of the ammeter(A) is 5 ampere and the current passing through the resistance R1, is 2 ampere then the value of the resistance R2, Is.—–
a-4W. b- 3W. c- 6W .
9-Four lamps 6W each are connected in parallel. The combination is connected to a 12V battery with a negligible internal resistance: The total resistance of the lamps equals……………
a)2/3W b) 24W c)3/2W d) 12W
10-Using the same data given in the previous question The current in each lamp is…………………………………
a) 3/2A b) 2A c) 2/3
11-When the circuit shown is connected, the 6V lamp glows. What happens to the brightness of the lamp when switch S is closed?
a-it becomes dimmer. b-it becomes brighter.
c-it goes off. d-it remains the same
In the circuit shown in the figure the switch S is open. When the switch is closed the reading of the ammeter changes from
0.5A to 1A b- 1A to 0.5A c- 1A to 2A
A cylindrical piece of a soft electrically-conducting material has resistance R. it is rolled out so that its length is doubled but its volume stays constant.
What is its new resistance?
a b-R c-2R d-4R
lf the length of a resistor is doubled and its cross-sectional area is decreased to one half, then its resistance becomes
a-Double its value b-4 times its value c-fixed
In which circuit from (a) to (e) will the current in R1 be different from that in R2?
D
In which circuit (a) to (e) is the effective resistance smallest?
D
In which circuit will the voltage across R1 be smaller than the resistance R2?
A
18-In the opposite fig the reading of ammeter is …..ampere
a-3/4 b-2 c1/2
Third; Important Give Reasons :
When no current passing through the electrical circuit the electromotive force of a battery equals the potential difference between its terminals.
Since the electromotive force of a battery is given by (VB= V+Ir ) therefore when no current passes through the circuit (the key is switched off ) the term Ir = 0 . Hence the potential difference between its terminals becomes equal to the electromotive force.
The electric conductivity of a conductor is considered as physical property to the material of such conductor ……
Because it depends on the type of the material and differ from one material to other at the same temperature.
Work must be done to transfer electric charges from one point to another.
Due to the existence of the potential difference between them .
Efficiency of the battery increases by the decrease of its internal resistance.
As , the efficiency of the battery is given by( V/V_B ×100=R/(R+r)×100) For that , when the internal resistance of the battery decrease the efficiency of the battery increase also, the lost of the work done (wasted energy) is reduced during operation.
In electric circuits connected in parallel, thick wires are used at the ends of the battery, but at the ends of each resistor less thick wires are used.
Because the current intensity in parallel circuits is greater at the input and output compared to the current in each branch.
The electrical conductivity of copper is high.
As the resistivity of copper is small
Connection of electrical devices in home in parallel. or The home electric devices are not connected in series.
In order to maintain the potential difference constant and increase the intensity of current across the devices. also, if a device is cut off, the other still operate.
Fourth; important Comparisons
The electrical conductivity and the resistivity from the point of view the definition of each , write the mathematical relation & the units.
Resistance and resistivity from the point of view the unit of each .
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