Current Electricity ICSE Class-10 Concise Physics Selina Solutions Chapter-8 . We Provide Step by Step Answer of Exercise-8(A), MCQs-8(A), Numericals-8(A), Exe-8(B), MCQ-8(B), Num-8(B) Exe-8(C), MCQ-8(C) and Num-8(C) Questions of Exercise-8 Current Electricity ICSE Class-10. Visit official Website CISCE for detail information about ICSE Board Class-10.
Board | ICSE |
Publications | Selina Publication |
Subject | Physics |
Class | 10th |
Chapter-8 | Current Electricity (Exercise 8A) |
Book Name | Concise |
Topics | Solution of Exercise-8(A), MCQs-8(A), Numericals-8(A), Exe-8(B), MCQ-8(B), Num-8(B) Exe-8(C), MCQ-8(C) and Num-8(C) |
Academic Session | 2021-2022 |
Current Electricity ICSE Class-10 Concise Physics Selina Solutions Chapter-8
-: Select Exercise :-
Exercise-8(A), MCQs-8(A), Numericals-8(A),
Exe-8(B), MCQ-8(B), Num-8(B) Exe-8(C), MCQ-8(C) and Num-8(C)
How to Solve Numericals of Current Electricity ICSE Class-10
Current Electricity deals with ohm’s law, concepts of E.M.F., Potential Difference, resistance, resistances in series and parallel; internal resistance also deals in Current Electricity. Concepts of P.D. Current Electricity in Physics of Chapter 8 and resistance and charge. Simple Numerical Problems using the above relations in Current Electricity.
“Current Electricity” Selina Solutions ICSE Physics , Exercise – 8 (A)
Page 186
Question 1
Define the term current and state its S.I. unit.
Answer 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 it’s S.I. unit.
Answer 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.
Answer 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’.
Answer 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.
Question 5
(a) State whether the current is a scalar or vector? What does the direction of current convey?
(b) State whether the potential is a scalar or vector? What does the positive and negative sign of potential convey?
Answer 5
(a) Current is a scalar quantity. The direction of current conveys that the flow of electrons is opposite to the direction of flow of current.
(b) Potential is also a scalar quantity. The positive sign of potential conveys that work has to be done on the positive test charge against the repulsive force due to the positive charge in bringing it from infinity. The negative sign of potential conveys that work is done on the negative test charge by the attractive force.
Question 6
Define the term resistance. State it’s S.I. unit.
Answer 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
(a) Name the particles which are responsible for the flow of current in a metallic wire.
(b) Explain the flow of current in a metallic wire on the basis of movement of the particles named by you above in part
(c) What is the cause of resistance offered by the metallic wire in the flow of current through it?
Answer 7
(a) Particles responsible for the flow of current in a metallic wire are free electrons.
(b) In metals, free electrons are the moving charges that result in the conduction of electricity. If ‘n’ electrons pass through the metallic conductor in time ‘t’, then the total charge that has flown is given by Q (charge) = n x e (charge on an electron).
(c) A metal includes free electrons and fixed positive ions.
Positive ions give away their valence electrons and thus attain a positive charge.
Electrons are free for movement, but positive ions do not move; thus, when a potential difference is applied across the circuit, and when free electrons begin to move, they collide with these fixed ions.
This collision is the major cause of resistance offered by the metallic wire in the flow of current through it.
Question 8 (Current Electricity ICSE Class-10 Concise)
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.
Answer 8
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 9
(a) Name and state the law which relates the potential difference and current in a conductor.
(b) What is the necessary condition for a conductor to obey the law named above in part (a)?
Answer 9
(a)The law is called Ohm’s law. It states that the current flowing through the conductor is directly proportional to the potential difference across the ends of a conductor given the temperature remains constant.
(b) Temperature should remain constant.
Question 10
(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?
Answer 10
(a)
(b) Slope of VI graph represents the resistance.
Question 11
Draw an I – V graph for a linear resistor. What does its slope represent?
Answer 11
The slope of I-V graph (= ) is equal to the reciprocal of the resistance of the conductor, i.e.
Question 12
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?
Answer 12
Ohmic Resistor: An ohmic resistor is a resistor that obeys Ohm’s law. For example: all metallic conductors (such as silver, aluminium, copper, iron etc.)
From above graph resistance is determined in the form of slope.
Question 13
What are non-ohmic resistors? Give one example and draw a graph to show its current-voltage relationship.
Answer 13
The conductors which do not obey Ohm’s Law are called non-ohmic resistors. Example: diode valve.
Question 14 (Current Electricity ICSE Class-10 Concise)
Give two differences between an ohmic and non-ohmic resistor.
Answer 14
(1) Ohmic resistor obeys ohm’s law i.e., V/I is constant for all values of V or I; whereas Non-ohmic resistor does not obey ohm’s law i.e., V/I is not same for all values of V or I.
(2) In Ohmic resistor, V-I graph is linear in nature whereas in non-ohmic resistor, V-I graph is non-linear in nature.
Question 15
Fig. 8.10 below shows the I-V curves for two resistors. Identify the ohmic and non-ohmic resistors. Give a reason for your answer.
Answer 15
Ohmic : (b), Non-Ohmic : (a)
Only for (a) the I-V graph is a straight line or linear while for (a), the graph is a curve.
Question 16
Draw a V – I graph for a conductor at two different temperatures. What conclusion do you draw from your graph for the variation of resistance of conductor with temperature?
Answer 16
In the above graph, T1 T2. The straight line A is steeper than the line B, which leads us to conclude that the resistance of conductor is more at high temperature T1 than at low temperature T2. Thus, we can say that resistance of a conductor increases with the increase in temperature.
Question 17
(a) How does the resistance of a wire depend on its radius? Explain your answer.
(b) Two copper wires are of same length, but one is thicker than the other. Which will have more resistance?
Answer 17
(a) Resistance of a wire is inversely proportional to the area of cross-section of the wire.
This means if a wire of same length, but of double radius is taken, its resistance is found to be one-fourth.
(b) Resistance is directly proportional to the length and inversely proportional to the area of cross-section. The thicker wire has more area, and hence the resistance of the other wire will be more than that of the thicker wire.
Question 18
How does the resistance of a wire depend on its length? Give a reason of your answer.
Answer 18
Resistance of a wire is directly proportional to the length of the wire.
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 19
How does the resistance of a metallic wire depend on its temperature? Explain with reason.
Answer 19
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 20
Two wires, one of copper and other of iron, are of the same length and same radius. Which will have more resistance? Give reason.
Answer 20
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 21
Name three factors on which the resistance of a wire depends and state how it is affected by the factors stated by you?
Answer 21
(i) Resistance of a wire is directly proportional to the length of the wire means with the increase in length resistance also increases.
(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.
(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 22 (Current Electricity ICSE Class-10 Concise)
Define the term specific resistance and state its S.I. unit.
Answer 22
The resistivity of a material is the resistance of a wire of that material of unit length and unit area of cross-section. Its S.I. unit is ohm metre.
Question 23
Write an expression connecting the resistance of a wire and specific resistance of its material. State the meaning of symbols used.
Answer 23
Expression :
– resistivity
R – resistance
l – length of conductor
A – area of cross- section
Question 24
State the order of specific resistance of (i) a metal, (ii) a semiconductor and (iii) an insulator.
Answer 24
Metal < Semiconductor < Insulator
Question 25
(a) Name two factors on which the specific resistance of a wire depends?
(b) Two wires A and B are made of copper. The wire A is long and thin while the wire B is Short and thick. Which will have more specific resistance ?
Answer 25
(a) The specific resistance of a wire depends on the material of the substance and the temperature of the substance.
(b) Specific resistance depends on the material of the wire and not its dimensions. Hence, both the wires will have the same specific resistance .
Page 187
Question 26
Name a substance of which the specific resistance remains almost unchanged by the increase in temperature.
Answer 26
Manganin
Question 27
How does specific resistance of a semi-conductor change with the increase in temperature?
Answer 27
Specific resistance of a semiconductor decreases with increase in temperature.
Question 28
How does (a) resistance, and (b) specific resistance of a wire depend on its (i) length, and (ii) radius?
Answer 28
Resistance is directly proportional to the length and inversely proportional to the square of radius. Specific resistance is independent on the dimensions of a wire.
Question 29
(a) Name the material used for making the connection wires. Give reason for your answer.
(b) Why should a connection wire be thick?
Answer 29
(a) The materials used for making connection wires are copper or aluminium. These materials are chosen because they have small specific resistance.
(b) A connection wire should be thick so that it offers negligible resistance to the flow of current through the circuit.
Question 30
Name a material which is used for making the standard resistor. Give a reason for your answer.
Answer 30
Manganin is used for making the standard resistor because its resistivity is quite large and the effect of change in temperature on their resistance is negligible.
Question 31
Name the material used for making a fuse wire. Give a reason.
Answer 31
Generally fuse wire is made of an alloy of lead and tin because its resistivity is high and melting point is low.
Question 32
Name the material used for:
(i) Filament of an electric bulb
(ii) Heating element of a room heater
Answer 32
(i) A wire made of tungsten is used for filament of electric bulb because it has a high melting point and high resistivity.
(ii) A nichrome wire is used as a heating element for a room heater because the resistivity of nichrome is high and increase in its value with increase in temperature is high.
Question 33 (Current Electricity ICSE Class-10 Concise)
What is a superconductor? Give one example of it.
Answer 33
A superconductor is a substance of zero resistance at a very low temperature. Example: Mercury at 4.2 K.
Question 34
A substance has zero resistance below 1 K. What is such a substance called?
Answer 34
Superconductor
Chapter 8 (A) MULTIPLE CHOICE TYPE Current Electricity Selina Physics Solutions
Page 187
Question 1
Which of the following is an ohmic resistance ?
(a) LED
(b) junction diode
(c) filament of a bulb
(d) nichrome wire
Answer 1
(d) nichrome wire
Question 2
For which of the following substances, resistance decreases with the increase in the temperature?
(a) copper
(b) mercury
(c) carbon
(d) platinum
Answer 2
(c) carbon
Numericals – 8 (A) “Current Electricity” Selina Physics Solutions ,
Page 187
Question 1
In a conductor 6.25 × electrons flow from its end A to B in 2 s. Find the current flowing through the conductor (e = 1.6 × C)
Answer 1
Number of electrons flowing through the conductor,
N = 6.25 × 1016 electrons
Time taken, t = 2 s
Given, e = 1.6 × 10-19 c
Let I be the current flowing through the conductor.
Then, I = net
∴ I = (6.25×1016)(1.6×10-19)2 =5×10-jA
Or, I = 5 mA
Thus, 5 Ma current flows from B to A.
Question 2
A current of 1.6 mA flows through a conductor. If charge on an electron is – 1.6 × coulomb, find the number of electrons that will pass each second through the cross section of that conductor.
Answer 2
Current , I =1.6 mA = 1.6 × A
Charge, Q = – 1.6 × coulomb
t = 1 sec
I = Q/t
Q = I x t
Q = 1.6 × × 1
No. of electrons = 1.6 × /1.6 ×
=
Question 3
Answer 3
Current (I) = 0.2 A
Resistance (R) = 20 ohm
Potential Difference (V) = ?
According to Ohm’s Law :
V = IR
V = 0.2 × 20 = 4 V
Question 4
An electric bulb draws 1.2 A current at 6.0 V. Find the resistance of filament of bulb while glowing.
Answer 4
Current (I) = 1.2 A
Potential Difference/Voltage (V) = 6.0 V
Resistance (R) = ?
According to Ohm’s Law :
V=IR
Then R = V/I
R = 6 / 1.2
R = 5 Ohm
Question 5
A car bulb connected to a 12 volt battery draws 2 A current when glowing. What is the resistance of the filament of the bulb? Will the resistance be more same or less when the bulb is not glowing?
Answer 5
Potential Difference/Voltage (V) = 12 V
Current (I) = 2 A
Resistance (R) = ?
According to Ohm’s Law :
V=IR
Then R = V/I
R = 12 / 2
R = 6 Ohm
Resistance will be less when the bulb is not glowing.
Question 6 (Current Electricity ICSE Class-10 Concise)
Calculate the current flowing through a wire of resistance 5 Ω connected to a battery of potential difference 3 V.
Answer 6
Potential Difference/Voltage (V) = 3 V
Resistance (R) = 5 ohm
Current (I) = ?
According to Ohm’s Law :
V=IR
Then I = V/R
I = 3/5 = 0.6 A
Question 7
In an experiment of verification of Ohm’s law following observations are obtained.
potential
difference V (in volt) |
0.5 | 1.0 | 1.5 | 2.0 | 2.5 |
current I ( in ampere) | 0.2 | 0.4 | 0.6 | 0.8 | 1.0 |
Draw a characteristic V –I graph and use this graph to find:
(a) the potential difference V when the current I is 0.5 A,
(b) the current I when the potential difference V is 0.75 V,
(c) the resistance in circuit.
Answer 7
(a) 1.25 V
(b) 0.3 A
(c) The graph is linear so resistance can be found from any value of the given table. For instance:
When V = 2.5 Volt
Current is I = 1.0 amp
According to ohm’s law :
R = V/I
R = 2.5/1.0 = 2.5 ohm
Question 8
Two wires of the same material and same length have radii r1 and r2 respectively compare: (i) their resistances, (ii) their resistivities.
Answer 8
(i) For wire of radius
Question 9 (Current Electricity ICSE Class-10 Concise)
A given wire of resistance 1 Ω is stretched to double its length. What will be its new resistance?
Answer 9
Let ‘I’ be the length and ‘a’ be the area of cross – section
of the resistor with resistance, R = 1Ω
when the wire is stretched to double its length,
the new length I’ = 2I and the new area of cross section,
a’ = a/2
∴ Resistance (R’) =
p=I′a′=p2Ia⁄2∴ R = 4p
Ia=4R∴ R = 4 × 1 = 4 Ω
Question 10
A wire of resistance 3 ohm resistance and length 10 cm is stretched to length 30 cm. Assuming that it has a uniform cross section, what will be its new resistance?
Answer 10
Resistance (R) = 3 ohm
Length l = 10 cm
New Length (l’) = 30 cm = 3 × l
R =
p 1A New Resistance :
With stretching length will increase and area of cross-section will decrease in the same order
R’ =
p 3A⁄3 Therefore,
R’ =
9 p 1/A=9 R
R’ = 9× 3 = 27Ω
Question 11
A wire of resistance 9 ohm having 30 cm is tripled on itself. What is its new resistance?
Answer 11
Resistance (R) = 9 ohm
Length l = 30 cm
New Length (l) = 30 cm = 3/l = 10 cm
Question 12 (Current Electricity ICSE Class-10 Concise)
What length of copper wire of resistivity 1.7 × 10-8 ? m and radius 1 mm is required so that its resistance is 1??
Answer 12
Resistance (R) = 1 ohm
Resistivity (ρ) = 1.7 x 10-8 ohm metre
Radius (r) = 1 mm = 10-3 m
Length (l) = ?
Question 13
The filament of a bulb takes a current 100 mA when potential difference across it is 0.2 V. When the potential difference across it becomes 1.0 V, the current becomes 400 mA. Calculate the resistance of filament in each case and account for the difference.
Answer 13
According to Ohm’s law,
Resistance of the wire increases with increase in temperature. So the difference arises because the temperature of the filament increased.
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