Selina Textbook Solutions: Current Electricity | Physics Class 10 ICSE PDF Download

 Page 1


Class X Chapter 8 – Current Electricity  Physics  
 
 
EXERCISE (8 A) 
 
Question 1:  
Define the term current and state its S.I unit. 
Solution 1: 
Current is defined as the rate of flow of charge. 
I = Q/t 
Its S.I. unit is Ampere. 
 
 
Question 2: 
Define the term electric potential. State its S.I. unit. 
Solution 2: 
Electric potential at a point is defined as the amount of work done in bringing a unit positive 
charge from infinity to that point. Its unit is the volt. 
 
 
Question 3: 
How is the electric potential difference between the two points defined? State its S.I. unit. 
Solution 3: 
The potential difference between two points is equal to the work done in moving a unit positive 
charge from one point to the other. 
It's S.I. unit is Volt. 
 
 
Question 4: 
Explain the statement ‘the potential difference between two points is 1 volt’. 
Solution 4: 
One volt is the potential difference between two points in an electric circuit when 1 joule of 
work is done to move charge of 1 coulomb from one point to other. 
 
 
 
 
 
Page 2


Class X Chapter 8 – Current Electricity  Physics  
 
 
EXERCISE (8 A) 
 
Question 1:  
Define the term current and state its S.I unit. 
Solution 1: 
Current is defined as the rate of flow of charge. 
I = Q/t 
Its S.I. unit is Ampere. 
 
 
Question 2: 
Define the term electric potential. State its S.I. unit. 
Solution 2: 
Electric potential at a point is defined as the amount of work done in bringing a unit positive 
charge from infinity to that point. Its unit is the volt. 
 
 
Question 3: 
How is the electric potential difference between the two points defined? State its S.I. unit. 
Solution 3: 
The potential difference between two points is equal to the work done in moving a unit positive 
charge from one point to the other. 
It's S.I. unit is Volt. 
 
 
Question 4: 
Explain the statement ‘the potential difference between two points is 1 volt’. 
Solution 4: 
One volt is the potential difference between two points in an electric circuit when 1 joule of 
work is done to move charge of 1 coulomb from one point to other. 
 
 
 
 
 
Class X Chapter 8 – Current Electricity  Physics  
 
 
 
 
Question 5: 
Explain the analogy between the flow of charge (or current) in a conductor under a potential 
difference with the free fall of a body under gravity. 
Solution 5: 
If a body is free to fall, on releasing it from a height, it falls downwards towards the earth's 
surface. For, this one end has to be at higher level and other at lower level, so that gravity could 
effect on this difference and body could freely fall. Same way to make flow of the charge through 
a conductor, the gravity of course has no role of play; there should be difference of electric 
potential. This difference gives the flow of charge in a conductor. 
 
 
Question 6: 
Define the term resistance. State its S.I. unit. 
Solution 6: 
It is the property of a conductor to resist the flow of charges through it. It's S.I. unit is Ohm. 
 
 
Question 7: 
Name the particles which are responsible for the flow of current in a metal. Explain the flow of 
current in a metal on the basis of movement of the particles name by you. 
Solution 7: 
In a metal, the charges responsible for the flow of current are the free electrons. The direction 
of flow of current is conventionally taken opposite to the direction of motion of electrons. 
 
 
Question 8: 
How does the resistance of a wire depend on its radius? Explain your answer. 
Solution 8: 
Resistance of a wire is inversely proportional to the area of cross-section of the wire. 
R ? 
1
?? 
R ? 
1
?? ?? 2
 
This means if a wire of same length, but of double radius is taken, its resistance is found to be 
one-fourth. 
 
 
Page 3


Class X Chapter 8 – Current Electricity  Physics  
 
 
EXERCISE (8 A) 
 
Question 1:  
Define the term current and state its S.I unit. 
Solution 1: 
Current is defined as the rate of flow of charge. 
I = Q/t 
Its S.I. unit is Ampere. 
 
 
Question 2: 
Define the term electric potential. State its S.I. unit. 
Solution 2: 
Electric potential at a point is defined as the amount of work done in bringing a unit positive 
charge from infinity to that point. Its unit is the volt. 
 
 
Question 3: 
How is the electric potential difference between the two points defined? State its S.I. unit. 
Solution 3: 
The potential difference between two points is equal to the work done in moving a unit positive 
charge from one point to the other. 
It's S.I. unit is Volt. 
 
 
Question 4: 
Explain the statement ‘the potential difference between two points is 1 volt’. 
Solution 4: 
One volt is the potential difference between two points in an electric circuit when 1 joule of 
work is done to move charge of 1 coulomb from one point to other. 
 
 
 
 
 
Class X Chapter 8 – Current Electricity  Physics  
 
 
 
 
Question 5: 
Explain the analogy between the flow of charge (or current) in a conductor under a potential 
difference with the free fall of a body under gravity. 
Solution 5: 
If a body is free to fall, on releasing it from a height, it falls downwards towards the earth's 
surface. For, this one end has to be at higher level and other at lower level, so that gravity could 
effect on this difference and body could freely fall. Same way to make flow of the charge through 
a conductor, the gravity of course has no role of play; there should be difference of electric 
potential. This difference gives the flow of charge in a conductor. 
 
 
Question 6: 
Define the term resistance. State its S.I. unit. 
Solution 6: 
It is the property of a conductor to resist the flow of charges through it. It's S.I. unit is Ohm. 
 
 
Question 7: 
Name the particles which are responsible for the flow of current in a metal. Explain the flow of 
current in a metal on the basis of movement of the particles name by you. 
Solution 7: 
In a metal, the charges responsible for the flow of current are the free electrons. The direction 
of flow of current is conventionally taken opposite to the direction of motion of electrons. 
 
 
Question 8: 
How does the resistance of a wire depend on its radius? Explain your answer. 
Solution 8: 
Resistance of a wire is inversely proportional to the area of cross-section of the wire. 
R ? 
1
?? 
R ? 
1
?? ?? 2
 
This means if a wire of same length, but of double radius is taken, its resistance is found to be 
one-fourth. 
 
 
Class X Chapter 8 – Current Electricity  Physics  
 
 
 
 
 
Question 9: 
How does the resistance of a wire depend on its length? Give a reason for your answer with 
reason. 
Solution 9: 
Resistance of a wire is directly proportional to the length of the wire. 
R ? I 
The resistance of a conductor depends on the number of collisions which the electrons suffer 
with the fixed positive ions while moving from one end to the other end of the conductor. 
Obviously the number of collisions will be more in a longer conductor as compared to a shorter 
conductor. Therefore, a longer conductor offers more resistance. 
 
 
Question 10: 
How does the resistance of a metallic wire depend on its temperature? Explain with reason. 
Solution 10: 
With the increase in temperature of conductor, both the random motion of electrons and the 
amplitude of vibration of fixed positive ions increase. As a result, the number of collisions 
increases. Hence, the resistance of a conductor increases with the increase in its temperature. 
The resistance of filament of a bulb is more when it is glowing (i.e., when it is at a high 
temperature) as compared to when it is not glowing (i.e., when it is cold). 
 
 
Question 11: 
Two wires one of copper and other of iron, are of the same length and same radius. Which will 
have more resistance? Give reason. 
Solution 11: 
Iron wire will have more resistance than copper wire of the same length and same radius because 
resistivity of iron is more than that of copper. 
  
 
Question 12: 
Name three factors on which resistance of a given wire depends and state how is it affected by 
the factors stated by you. 
Solution 12: 
(i) Resistance of a wire is directly proportional to the length of the wire means with the increase 
in length resistance also increases. 
Page 4


Class X Chapter 8 – Current Electricity  Physics  
 
 
EXERCISE (8 A) 
 
Question 1:  
Define the term current and state its S.I unit. 
Solution 1: 
Current is defined as the rate of flow of charge. 
I = Q/t 
Its S.I. unit is Ampere. 
 
 
Question 2: 
Define the term electric potential. State its S.I. unit. 
Solution 2: 
Electric potential at a point is defined as the amount of work done in bringing a unit positive 
charge from infinity to that point. Its unit is the volt. 
 
 
Question 3: 
How is the electric potential difference between the two points defined? State its S.I. unit. 
Solution 3: 
The potential difference between two points is equal to the work done in moving a unit positive 
charge from one point to the other. 
It's S.I. unit is Volt. 
 
 
Question 4: 
Explain the statement ‘the potential difference between two points is 1 volt’. 
Solution 4: 
One volt is the potential difference between two points in an electric circuit when 1 joule of 
work is done to move charge of 1 coulomb from one point to other. 
 
 
 
 
 
Class X Chapter 8 – Current Electricity  Physics  
 
 
 
 
Question 5: 
Explain the analogy between the flow of charge (or current) in a conductor under a potential 
difference with the free fall of a body under gravity. 
Solution 5: 
If a body is free to fall, on releasing it from a height, it falls downwards towards the earth's 
surface. For, this one end has to be at higher level and other at lower level, so that gravity could 
effect on this difference and body could freely fall. Same way to make flow of the charge through 
a conductor, the gravity of course has no role of play; there should be difference of electric 
potential. This difference gives the flow of charge in a conductor. 
 
 
Question 6: 
Define the term resistance. State its S.I. unit. 
Solution 6: 
It is the property of a conductor to resist the flow of charges through it. It's S.I. unit is Ohm. 
 
 
Question 7: 
Name the particles which are responsible for the flow of current in a metal. Explain the flow of 
current in a metal on the basis of movement of the particles name by you. 
Solution 7: 
In a metal, the charges responsible for the flow of current are the free electrons. The direction 
of flow of current is conventionally taken opposite to the direction of motion of electrons. 
 
 
Question 8: 
How does the resistance of a wire depend on its radius? Explain your answer. 
Solution 8: 
Resistance of a wire is inversely proportional to the area of cross-section of the wire. 
R ? 
1
?? 
R ? 
1
?? ?? 2
 
This means if a wire of same length, but of double radius is taken, its resistance is found to be 
one-fourth. 
 
 
Class X Chapter 8 – Current Electricity  Physics  
 
 
 
 
 
Question 9: 
How does the resistance of a wire depend on its length? Give a reason for your answer with 
reason. 
Solution 9: 
Resistance of a wire is directly proportional to the length of the wire. 
R ? I 
The resistance of a conductor depends on the number of collisions which the electrons suffer 
with the fixed positive ions while moving from one end to the other end of the conductor. 
Obviously the number of collisions will be more in a longer conductor as compared to a shorter 
conductor. Therefore, a longer conductor offers more resistance. 
 
 
Question 10: 
How does the resistance of a metallic wire depend on its temperature? Explain with reason. 
Solution 10: 
With the increase in temperature of conductor, both the random motion of electrons and the 
amplitude of vibration of fixed positive ions increase. As a result, the number of collisions 
increases. Hence, the resistance of a conductor increases with the increase in its temperature. 
The resistance of filament of a bulb is more when it is glowing (i.e., when it is at a high 
temperature) as compared to when it is not glowing (i.e., when it is cold). 
 
 
Question 11: 
Two wires one of copper and other of iron, are of the same length and same radius. Which will 
have more resistance? Give reason. 
Solution 11: 
Iron wire will have more resistance than copper wire of the same length and same radius because 
resistivity of iron is more than that of copper. 
  
 
Question 12: 
Name three factors on which resistance of a given wire depends and state how is it affected by 
the factors stated by you. 
Solution 12: 
(i) Resistance of a wire is directly proportional to the length of the wire means with the increase 
in length resistance also increases. 
Class X Chapter 8 – Current Electricity  Physics  
 
 
 
 
R ? I 
(ii) Resistance of a wire is inversely proportional to the area of cross-section of the wire. If area 
of cross-section of the wire is more, then resistance will be less and vice versa. 
R ? 
1
?? 
(iii) Resistance increases with the increase in temperature since with increase in temperature the 
number of collisions increases. 
(iv) Resistance depends on the nature of conductor because different substances have different 
concentration of free electrons. Substances such as silver, copper etc. offer less resistance and 
are called good conductors; but substances such as rubber, glass etc. offer very high resistance 
and are called insulators. 
 
 
Question 13: 
State Ohm’s law and draw a neat labelled circuit diagram containing a battery, a key, a voltmeter, 
an ammeter, a rheostat and an unknown resistance to verify it. 
Solution 13: 
It states that electric current flowing through a metallic wire is directly proportional to the 
potential difference V across its ends provided its temperature remains the same. This is called 
Ohm's law. 
V = IR 
 
 
 
Question 14: 
What is the necessary condition for a conductor to obey Ohm’s law? 
Solution 14: 
Ohm's law is obeyed only when the physical conditions and the temperature of the conductor 
remain constant. 
 
 
Page 5


Class X Chapter 8 – Current Electricity  Physics  
 
 
EXERCISE (8 A) 
 
Question 1:  
Define the term current and state its S.I unit. 
Solution 1: 
Current is defined as the rate of flow of charge. 
I = Q/t 
Its S.I. unit is Ampere. 
 
 
Question 2: 
Define the term electric potential. State its S.I. unit. 
Solution 2: 
Electric potential at a point is defined as the amount of work done in bringing a unit positive 
charge from infinity to that point. Its unit is the volt. 
 
 
Question 3: 
How is the electric potential difference between the two points defined? State its S.I. unit. 
Solution 3: 
The potential difference between two points is equal to the work done in moving a unit positive 
charge from one point to the other. 
It's S.I. unit is Volt. 
 
 
Question 4: 
Explain the statement ‘the potential difference between two points is 1 volt’. 
Solution 4: 
One volt is the potential difference between two points in an electric circuit when 1 joule of 
work is done to move charge of 1 coulomb from one point to other. 
 
 
 
 
 
Class X Chapter 8 – Current Electricity  Physics  
 
 
 
 
Question 5: 
Explain the analogy between the flow of charge (or current) in a conductor under a potential 
difference with the free fall of a body under gravity. 
Solution 5: 
If a body is free to fall, on releasing it from a height, it falls downwards towards the earth's 
surface. For, this one end has to be at higher level and other at lower level, so that gravity could 
effect on this difference and body could freely fall. Same way to make flow of the charge through 
a conductor, the gravity of course has no role of play; there should be difference of electric 
potential. This difference gives the flow of charge in a conductor. 
 
 
Question 6: 
Define the term resistance. State its S.I. unit. 
Solution 6: 
It is the property of a conductor to resist the flow of charges through it. It's S.I. unit is Ohm. 
 
 
Question 7: 
Name the particles which are responsible for the flow of current in a metal. Explain the flow of 
current in a metal on the basis of movement of the particles name by you. 
Solution 7: 
In a metal, the charges responsible for the flow of current are the free electrons. The direction 
of flow of current is conventionally taken opposite to the direction of motion of electrons. 
 
 
Question 8: 
How does the resistance of a wire depend on its radius? Explain your answer. 
Solution 8: 
Resistance of a wire is inversely proportional to the area of cross-section of the wire. 
R ? 
1
?? 
R ? 
1
?? ?? 2
 
This means if a wire of same length, but of double radius is taken, its resistance is found to be 
one-fourth. 
 
 
Class X Chapter 8 – Current Electricity  Physics  
 
 
 
 
 
Question 9: 
How does the resistance of a wire depend on its length? Give a reason for your answer with 
reason. 
Solution 9: 
Resistance of a wire is directly proportional to the length of the wire. 
R ? I 
The resistance of a conductor depends on the number of collisions which the electrons suffer 
with the fixed positive ions while moving from one end to the other end of the conductor. 
Obviously the number of collisions will be more in a longer conductor as compared to a shorter 
conductor. Therefore, a longer conductor offers more resistance. 
 
 
Question 10: 
How does the resistance of a metallic wire depend on its temperature? Explain with reason. 
Solution 10: 
With the increase in temperature of conductor, both the random motion of electrons and the 
amplitude of vibration of fixed positive ions increase. As a result, the number of collisions 
increases. Hence, the resistance of a conductor increases with the increase in its temperature. 
The resistance of filament of a bulb is more when it is glowing (i.e., when it is at a high 
temperature) as compared to when it is not glowing (i.e., when it is cold). 
 
 
Question 11: 
Two wires one of copper and other of iron, are of the same length and same radius. Which will 
have more resistance? Give reason. 
Solution 11: 
Iron wire will have more resistance than copper wire of the same length and same radius because 
resistivity of iron is more than that of copper. 
  
 
Question 12: 
Name three factors on which resistance of a given wire depends and state how is it affected by 
the factors stated by you. 
Solution 12: 
(i) Resistance of a wire is directly proportional to the length of the wire means with the increase 
in length resistance also increases. 
Class X Chapter 8 – Current Electricity  Physics  
 
 
 
 
R ? I 
(ii) Resistance of a wire is inversely proportional to the area of cross-section of the wire. If area 
of cross-section of the wire is more, then resistance will be less and vice versa. 
R ? 
1
?? 
(iii) Resistance increases with the increase in temperature since with increase in temperature the 
number of collisions increases. 
(iv) Resistance depends on the nature of conductor because different substances have different 
concentration of free electrons. Substances such as silver, copper etc. offer less resistance and 
are called good conductors; but substances such as rubber, glass etc. offer very high resistance 
and are called insulators. 
 
 
Question 13: 
State Ohm’s law and draw a neat labelled circuit diagram containing a battery, a key, a voltmeter, 
an ammeter, a rheostat and an unknown resistance to verify it. 
Solution 13: 
It states that electric current flowing through a metallic wire is directly proportional to the 
potential difference V across its ends provided its temperature remains the same. This is called 
Ohm's law. 
V = IR 
 
 
 
Question 14: 
What is the necessary condition for a conductor to obey Ohm’s law? 
Solution 14: 
Ohm's law is obeyed only when the physical conditions and the temperature of the conductor 
remain constant. 
 
 
Class X Chapter 8 – Current Electricity  Physics  
 
 
 
 
Question 15: 
(a) draw a V-I graph for a conductor obeying Ohm’s law. (b) what does the slope of V–I graph 
for a conductor represent?                              
Solution 15: 
 
Slope of V-I graph represents the Resistance. 
 
 
Question 16: 
Draw a I – V graph for a linear resistor. What does its slope represent? 
Solution 16: 
 
The slope of I-V graph (= 
?I
??
 ) is equal to the reciprocal of the resistance of the conductor, i.e. 
Slope = 
?
??
?
= 
1
Resistance of conductor
 = Conductance  
 
 
 
Question 17: 
What is an ohmic resistor? Give one example of an ohmic resistor. Draw a graph to show its 
current voltage relationship. How is the resistance of the resistor determined from this graph.