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Title: Physics chapter 1 notes
Description: This is the summary note of physics chapter 1
Description: This is the summary note of physics chapter 1
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CHAPTER – 12
ELECTRICITY
Think life without “electricity” in this modern society
...
Since we are science student, so it
is necessary to understand the basic concept behind the word “electricity”
Charge®
(q)
It is a very small particles present in an atom it can be either negative (electron) or
positive (proton)
“Coulomb” is the SI unit of charge, represented by C
...
6 ´
n=
Q
1
=
–19
e
1
...
2 ´
10
16
18
n=6´
10 electron
Current (I)
Rate of flow of net charge is called current
...
by A
...
1A =
1C
1s
124
X-Science
In an electric circuit the electric current flow in the opposite direction of the flow of
electron (–ve charge) conventionally
...
Small quantity of current are expressed in
–3
mA (milli Ampere) = 10 A
–6
uA (micro Ampere) = 10 A
Ammeter– It is an instrument used to measure the electric current in a circuit
...
It has
low resistance
...
Bulb
The arrow shows the direction
of electric current in circuit
...
Battery
(Having 3 cells)
The electron can only flow when there is difference of electric pressure
...
In case of electric current, the flow of charge is made possible due to chemical
action with in a cell that generates the potential difference across the terminals of
the cell
...
Electric potential Difference– It is defined as the work done in carrying a unit
charge from one point to another between the two points of an electric circuits
...
by “V”
V=
W
Q
125
X-Science
One Volt ®
When 1 Joule of work is done to carry one coulomb (1C) of charge
from one point to another of a current carrying conductor then the potential
difference is send to be IV
...
It is always
connected in parallel across the points between which the potential difference is to
be measured
...
Symbols for some commonly used instrument in circuit diagrams
+
(1) Cell
(2) Battery
–
+
–
(3) Key (switch) open
OR
(4) Key (Close)
OR
(5) Joint wire
(6) Wires with no join
(7) Bulb
+
(8) Ammeter
+
(9) Voltmeter
126
A
V
–
–
X-Science
Georg Simon Ohm (physicist) 1787 – 1854
Found the relationship between the current (I) flowing through a conductor and
potential difference (V) across the terminals of a conductor using the circuit
diagram
...
Resistance– It is the property of a conductor that opposes the flow of current
...
V = IR
\
R= V
I
1 Ohm or 1 W
= 1V
1A
127
X-Science
Rheostate–
As we know that
V = IR
{
Shows that current through
\
1= V
conductor resistor is inversely
R
proportional is its resistance
}
So to increase or decrease the current accordingly in the circuit a component is
used is called “Rheostat”, that regulates the current without changing potential
difference
...
FACTORS ON WHICH RESISTANCE OF A CONDUCTOR DEPENDS–
(1) On its length (l)
(2) On its cross sectional area (A)
(3) On the nature of material
(Resistance)
Ra
l
1
Ra
A
l
Ra
A
R= l
A
(Directly prop
...
11
...
l
Since R =
Its SI unit is W
m
A
R
...
m2
\
==
l
m
\
SI unit of =
W
m
...
128
X-Science
Resistantly of a material vary with temperature
Resistivity of an alloy (homogeneous mixture of metals) is generally higher than
of its constituent metals
...
For example “Tungsten” as filament of electric bulb
...
R1
R2
R3
V1
V2
V3
I
+
–
V
Ohm’s low stated
V = IR
The current (I) flowing through the resistance in series will remain same, where as
the potential difference (V) across each resistor will be different
...
Resistance in Parallel (Minimum Effective Resistance)
Let us take three R1, R2 and R3, that are connected in parallel in the electric circuit
...
Disadvantage of series connection in on electric circuit :–
1
...
TV, bulb, fan
...
2
...
Hence, to overcome this problem we generally use parallel circuit
...
Battery or Cell
(Chemical reaction in
it will produce potential
difference at its
two terminals)
Rest of energy of source is
converted into heat, that
raises the temperature
of gadget
...
130
X-Science
Mathematical Expression :–
Let us suppose that current (I) is flowing through a resistor of resistance (R) for the
time (t)
...
W
V= Q
\
Work done in morning the charge Q will be
W = VQ
W
Then power, P = t [Rate of change of work done]
VQ
= t
Q
P = VI
I= t
– (1)
Heat energy supplied by the source for time t will be
Energy or Work
H=P´
t
P=
– (2)
time
Put equation (i) in equation (2)
H = VIt
= (IR) It
\
V = IR Ohm’s Law]
2
H = I Rt
This is known as Joule’s Law
The law stated that the heat produced in a resistor is
(i) directly proportional to square of the current(I)
(ii) directly proportional to resistance (R) for given current
(iii) directly proportional to time (t) for which current flow through resistor
...
(2) It is also used in bulb to produce light
...
pt = 3380°C)
...
The wire of fuse is made of an alloy of metals for ex Aluminium Copper, Iron
131
X-Science
lead etc
...
pt and high resistivity, fuse is always
connected in series circuit
...
This melts the fuse wire and break the
circuit
...
for
various operation depending upon the power of appliance using
...
54A
In this case a 5A fuse is required
...
P = VI
or P = I2R
2
V
or P =
R
( V = IR Ohm’s Law)
( I= V )
R
or P = Electrical Energy (E)
time (t)
SI unit of electric power is “Watt” (W)
...
P = VI
1 Watt = 1 Volt ´
1 Ampere
29 Electrical Energy–
P= E
t
E – Electrical Energy
t – time
\
E=P´
t
132
X-Science
SI unit of electrical energy = Ws or J
Commercial unit of electrical energy = KWh or One unit
E=P´
t
\
KWh = 1KW ´
h
= 1000W ´
3600 s
5
= 36 ´
10 Ws
= 3
...
6 ´
106J
One horse power = 746W
133
X-Science
EXERCISE
(Question Bank)
Very Short Answers (1 Mark)
1
...
What is the conventional direction of flow of current?
3
...
On what factors does the resistance of a conductor depend?
5
...
6
...
Why the filament of bulb has high melting point?
8
...
What is the relationship between power, current and potential difference
(Ans : P = VI)
10
...
Draw a schematic diagram of a circuit consisting of a battery of six cell of
1
...
2
...
Draw the graph between V&I?
3
...
A wire of length L and R is stretched so that its length’s doubled and the area
of cross section is halved
...
134
X-Science
5
...
Does it require fuse of 5A, give reason?
6
...
On what factor the resistance of conductor depends give its mathematical
expression
...
3mm?
2
...
(1)
Calculate total effective resistance
(2)
The total current through the circuit
...
Three resistance of 2W
, 3W
and 5W
are connected in the electric circuit
Title: Physics chapter 1 notes
Description: This is the summary note of physics chapter 1
Description: This is the summary note of physics chapter 1