NCERT Class 10 Science Notes on Electricity
Get FREE Notes of NCERT Class 10 Science Notes on Electricity. Here you will get Class 10 NCERT Science Notes on Electricity of Chapter 12. These notes are prepared by well-experienced teachers which will very helpful for the students for making notes without wasting their precious time, directly you can read notes from here and can prepare for the examination.
Name of Book: SCIENCE TEXTBOOK FOR CLASS X
Published By: NCERT
Chapter: 12
Chapter Name: Electricity
Page Number: 199
Who can Read: Anyone, CBSE, ICSE, STATE & useful for other competitive Exam like NEET, JEE, IIT, CAT, TET, CTET, BANK Exam, Railway Exam, SSC, UPSC, ACS, etc
Also, you can check: Class 10 Advanced Mathematics Solutions Pdf
Brief Introduction:
There is hardly any field where electricity is not needed. Its importance can be felt at once when the electricity of our city breaks down. Here, we shall discuss the basic concepts of electricity.
ELECTRIC CURRENT AND CIRCUIT
We are familiar with air current and water current. We know
that flowing water constitutes water current in rivers. Similarly, if the
electric charge flows through a conductor (for example, through a metallic
wire), we say that there is an electric current in the conductor.
A switch makes a
conducting link between the cell and the bulb.
A continuous and closed path of an electric current is called an electric circuit.
Now, if the circuit is broken anywhere (or the switch of the
torch is turned off), the current stops flowing and the bulb does not glow.
How do we express electric current?
Electric current is expressed by the amount of charge flowing through a particular area in unit time. In other words, it is the rate of flow of electric charges.
Types of Electric Charge:
a) Positive Charge: Electric
current was considered to be the flow of positive charges and the direction of
flow of positive charges was taken to be the direction of electric current.
b) Negative Charge: Electric
circuit the direction of the electric current is taken as opposite to the direction
of the flow of electrons, which are negative charges.
Like or similar
charges repel each other. And unlike charges attract each other.
ELECTRIC CURRENT
An electric current is defined as the amount of charge
flowing through any cross-section of a conductor in unit time.
If a net charge Q flows across any cross-section of a
conductor in time t, then the current I, through the cross-section is
Electric Current (I)=charge (Q)/time (t)
OR I=Q/t
Units of Electric Current:
The SI unit of electric charge is the coulomb (C), which is
equivalent to the charge contained in nearly 6 × 10＾18 electrons. We know that an
electron possesses a negative charge of 1.6 × 10–19 C.
Definitions of Ampere:
Electric current through a conductor is said to be 1 ampere
if a one-coulomb charge flows through any cross-section of the conductor in one
second.
The electric current is expressed by a unit called ampere
(A), named after the French scientist, Andre-Marie Ampere (1775–1836).
Smaller Units of Electric Current:
Quantities of current are expressed in milliampere
1 mA = 10–3 A
or in microampere
1 µA = 10–6 A
What is Ammeter ??
An instrument called an ammeter measures electric
current in a circuit.
It is always
connected in series in a circuit through which the current is to be measured.
ELECTRIC CIRCUIT:
An electric circuit
is a closed conducting path containing a source of potential difference or
electric energy and a device or element utilizing the electric energy.
ELECTRIC POTENTIAL:
We define the electric potential difference between two
points in an electric circuit carrying some current as the work done to move a
unit charge from one point to the other –
Potential difference (V) between two points = Work done
(W)/Charge (Q)
V=W/Q
The SI unit of electric potential difference is volt (V),
named after Alessandro Volta (1745–1827), an Italian physicist.
One volt is the potential difference between two points in a
current-carrying conductor when 1 joule of work is done to move a charge of 1
coulomb from one point to the other.
1 volt=1 joule/1 columb
The potential difference is measured by means of an instrument called the voltmeter.
The voltmeter is always connected in parallel across the points between which the potential difference is to be measured.
CIRCUIT DIAGRAM:
We know that an electric circuit, comprises a cell (or a
battery), a plug key, electrical component(s), and connecting wires. It is
often convenient to draw a schematic diagram, in which different components of
the circuit are represented by the symbols conveniently used.
OHM’S LAW:
State Ohm's law?: The potential difference, V, across the ends of a given
metallic wire in an electric circuit is directly proportional to the current
flowing through it, provided its temperature remains the same. This is called Ohm’s law. In other words –
V∝ I
or V/I = constant = R
or V =IR
R is a constant for the given metallic wire at a given
temperature and is called its resistance.
What is Resistance ???
It is the property of a conductor to resist the flow of
charges through it. Its SI unit is the ohm, represented by the Greek letter Ω.
According to Ohm’s law, R=V/I
If the potential difference across the two ends of a
conductor is 1 V and the current through it is 1 A, then the resistance R, of
the conductors 1 Ω. That is, 1 ohm=1 volt/1 ampere
So get I=V/R
It is obvious from I=V/R that the current through a resistor
is inversely proportional to its resistance. If the resistance is doubled the
current gets halved.
In many practical cases, it is necessary to increase or
decrease the current in an electric circuit. A component used to regulate
current without changing the voltage source is called variable resistance.
In an electric circuit, a device called rheostat is often
used to change the resistance in the circuit.
FACTORS ON WHICH THE RESISTANCE OF A CONDUCTOR DEPENDS:
On applying Ohm’s law we observe that the resistance of the
conductor depends
(i) on its length,
(ii) on its area of cross-section, and
(iii) on the nature of its material.
Precise measurements have shown that the resistance of a uniform metallic conductor is directly proportional to its length (l) and inversely
proportional to the area of cross-section (A).
That is, R ∝ l (i) and
R ∝ 1/A (ii)
Combining Eqs. (i) and (ii) we get,
R ∝ l /A
or, R = ρ l /A
where ρ (rho) is a constant of proportionality and is called
the electrical resistivity of the material of the conductor. The SI unit of
resistivity is Ω m.
Electric current through a conductor is said to be 1 ampere if a one-coulomb charge flows through any cross-section of the conductor in one second.
The electric current is expressed by a unit called ampere (A), named after the French scientist, Andre-Marie Ampere (1775–1836).
3. Calculate the number of electrons constituting one coulomb of charge.
Answer: One electron possesses a charge of 1.6 × 10–19 C, i.e.,1.6 × 10–19 C of charge is contained in 1 electron.
∴ 1 C of charge is contained in 1/1.6 × 10–19 C= 6.25 × 10^18 C electrons.
Therefore, 6 × 10^18 electrons constitute one coulomb of charge.
Example 12.2 How much work is done in moving a charge of 2 C across two points having a potential difference of 12 V?
Solution: The amount of charge Q, that flows between two points at potential difference V (= 12 V) is 2 C.
Thus, the amount of work W, done in moving the charge [from Eq. (12.2)] is
W = VQ = 12 V × 2 C = 24 J.
INTEXT QUESTIONS || Page No. 202
1. Name a device that helps to maintain a potential difference across a conductor.
A source of electricity such as cell, battery, power supply, etc helps to maintain a potential difference across a conductor.
2. What is meant by saying that the potential difference between two points is 1 V?
Answer: One volt is the potential difference between two points in a current-carrying conductor when 1 joule of work is done to move a charge of 1 coulomb from one point to the other.
1 volt=1 joule/1 columb
3. How much energy is given to each coulomb of charge passing through a 6 V battery?
Answer: The amount of charge Q, that flows between two points at potential difference V (= 6 V) is 1 C.
Thus, the amount of work W, done in moving the charge [from Eq. (12.2)] is
Work Done, W = VQ = 6 V × 1 C = 6 J.
∴ 6 J of energy is given to each coulomb of charge passing through a battery of 6 V.
Example 12.3 (a) How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω?
(b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 Ω?
Solution:(a) We are given V = 220 V; R = 1200 Ω.
From Eq. (12.6), we have the current I = 220 V/1200 Ω = 0.18 A.
(b) We are given, V = 220 V, R = 100 Ω.
From Eq. (12.6), we have the current I = 220 V/100 Ω = 2.2 A.
Note the difference of current drawn by an electric bulb and electric heater from the same 220 V source!
Example 12.4 The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V?
Solution We are given, potential difference V = 60 V, current I = 4 A.
According to Ohm’s law,
R=V/I = 60 V/ 4 A = 15 Ω
When the potential difference is increased to 120 V the current is given by
current = I=V/R = 120 V / 15 Ω = 8 A
The current through the heater becomes 8 A.
Example 12.5 Resistance of a metal wire of length 1 m is 26 Ω at 20°C. If the diameter of the wire is 0.3 mm, what will be the resistivity of the metal at that temperature? Using Table 12.2, predict the material of the wire.
Solution: We are given the resistance R of the wire = 26 Ω, the diameter d = 0.3 mm = 3 × 10-4 m, and the length l of the wire = 1 m.
Therefore, from Eq. (12.10), the resistivity of the given metallic wire is
ρ = (RA/l) = (R π d^2/4l)
Substitution of values in this gives
ρ = 1.84 × 10–6 Ω m
The resistivity of the metal at 20°C is 1.84 × 10–6 Ω m.
From Table 12.2, we see that this is the resistivity of manganese.
INTEXT QUESTIONS || Page No. 204
1. On what factors does the resistance of a conductor depend?
Answer: On applying Ohm’s law we observe that the resistance of the conductor depends
(i) on its length,
(ii) on its area of cross-section, and
(iii) on the nature of its material.
2. Will current flow more easily through a thick wire or a thin wire of the same material, when connected to the same source? Why?
Answer: R = ρ l /A
where Resistivity of the material of the wire
l= Length of the wire
A = Area of a cross-section of the wire
Resistance is inversely proportional to the area of the cross-section of the wire.
Thicker the wire, lower is the resistance of the wire, and vice-versa. Therefore, current can flow more easily through a thick wire than a thin wire.
3. Let the resistance of an electrical component remains constant while the potential difference across the two ends of the component decreases to half of its former value. What change will occur in the current through it?
Answer: The change in the current flowing through the component is given by Ohm's law as,
V = IR
I = V / R
where R = resistance of the electrical component
V = Potential difference
I = Current
The potential difference is reduced to half, keeping resistance constant.
Let the new resistance be R and the new amount of current be I.
Therefore, from Ohm's law, we obtain the amount of new current.
I'= V' / R' = (V / 2)/ R = 1/ 2 ｘ (V / R ) = I / 2
Therefore, the amount of current flowing through the electrical component is reduced by half.
0 Comments