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2. Electric Current and Circuit
Electric Potential & Potential Difference
Circuit Diagram
Ohm’s Law
Factors on which the Resistance of a
conductor Depends -Resistance & Resistivity
Resistance of a System of Resistors-
Series/Parallel
Heating Effects of Current
Electric Power

3. It is a form of Energy made up of charges
that can produce light, heat or motion
Static electricity – electric charges at rest
Current electricity – electric charges -
motion

4. Flow of electric charge constitutes
electric current

5.  Other examples –
 glass rod rubbed with silk cloth
 An ebonite rod rubber with woolen cloth

6.  Positive Charge
 Negative Charge
 Property of Electric Charges:
Opposite charges attract each other
Similar charges repel each other

13.  SI unit of electric charge is coulomb which is
denoted by C
 One Coulomb is that quantity of electric
charge which exerts a force of 9 x 109
Newton's on an equal charge placed at a
distance of 1 metre from it.

14.  Q = n x e
where –
Q – charge in coulombs
n- number of electrons(integer)
e – charge of one electron = 1.6 x 10 -19 C
So, 1 C = n x 1.6 x 10 -19 C
n = 1C/1.6 x10 -19 C
n = 6.25 x 1018 electrons
Hence, we can say that one coulomb of electric
charge contains 6.25 x 10 18 electrons

18.  Flow of electric charge constitutes electric
current
 Definition: Electric current is expressed by
the amount of charge flowing through a
particular area in unit time.
 It is the rate of flow of electric charges.
 Denoted by I

19.  The magnitude of an electric current is defined
as the amount of electrons passing through a
cross-sectional area of the wire within a given
interval of time.
 Current = amount of electrons flowing through
the cross-section of the wire
 I = Q/ t
 Where,
 I – amount of current
 Q- amount of electrons flowing through a cross section
 t- time taken

22.  The SI unit of current is Ampere, named after the great
physicist, Andre Marie Ampere
 Since the SI unit of charge is coulomb and that of time
is second, we define 1 ampere as:
 1 ampere is 1 coulomb of charge flowing through a
conductor in one second.
 1 A = 1 C/ 1 s
 or 1 C = 1A x 1S
 So, 1 coulomb can be defined as the amount of charge
that passes through a conductor when 1 ampere
current flows through the conductor for 1 second.

23.  An ammeter is used to measure the
electric current in a circuit. It is always
connected in series.

24.  The smaller units of current are
expressed in milliampere (mA)
and micro ampere(µA). The
relation is given by:
 1mA = 10-3 A
 1µA = 10-6A

26.  So, Direction of current for
- Electronic current is – from –ve to +ve
- Conventional current – from +ve to -ve

27.  What does an electric current mean?
 Define the unit of current.
 Calculate the number of electrons
constituting one coulomb of charge.
 An electric bulb draws a current of 0.25 A for
20 min. calculate the amount of electric
charge that flows through the circuit.
 Calculate the current in a circuit if 500 C of
charge passes through it in 10 min.
 An electric iron draws a current of 0.6 A when
the voltage is 100 volt. Calculate the amount
of electric charge flowing through it in one
hour.

28.  Why do we get electric shock, if we touch a live
wire?
 Birds sitting on a live wire, does not get
electrocuted, why?

30.  Electric potential at a point in an electric
field is defined as the work done in
moving a unit positive charge from infinity
to that point.
 It is denoted by V
 Its unit is Volt
 A potential of 1 volt at a point means that
1 joule of work is done in moving 1 unit
positive charge(1 C) from infinity to that
point.

31.  The difference in electric potential between two
points is known as potential difference.
 The potential difference between two points in
an electric circuit is defined as the amount of
work done in moving a unit charge from one
point to the other point.
 So,
Potential difference = Work done
Quantity of charge moved

32. V = W/ Q
 Where,
 V –potential difference
 W – work done
 Q – Quantity of charge moved

33.  SI unit of potential difference is volt and
denoted by V
 The potential difference between two points is
said to be 1 volt if 1 joule of work is done in
moving 1 coulomb of electric charge from one
point to the other.
 So, 1 volt = 1 joule/ 1 coulomb
 Or 1 V = 1J/ 1C

34.  Potential difference is measured by means of
an instrument called voltmeter
 Voltmeter is always connected in parallel
 Voltmeter has high resistance

35.  Name a device that helps to maintain a
potential difference across a conductor.
 What is meant by saying that the potential
difference between two points is 1 V?
 How much work is done in moving a charge
of 2C across two points having a potential
difference 12V?
 How much work is done in moving a charge
of 2 coulombs from a point at 118 volts to a
point at 128 volts?
 How much energy is given to each coulomb
of charge passing through a 6 V battery?

36.  A continuous conducting path consisting
of wires and other resistances( like electric
bulb etc )and a switch, between the two
terminals of a cell or a battery along which
an electric current flows, is called a circuit.

38.  A diagram which indicates how different
components in a circuit have been connected
by using the electrical symbols for the
components, is called a circuit diagram

42.  The ratio of V/I is same i.e. a constant
value.
 The graph drawn between V-I is a straight
line that passes through the origin of the
graph, showing that current is directly
proportional to the potential difference.

43.  States that:
 The potential difference, V , across
the ends of a given metallic wire in an
electric circuit is directly proportional
to the current, I, flowing through it,
provided its temperature remains the
same(constant)

44.  V α I
 V = Constant x I
 V/ I = R
 Where V = Potential difference
 I = Electric current
 R = Resistance

45.  Resistance is the property of a conductor due to
which it opposes the flow of current flowing
through it.
R = V/I
 The unit of resistance is Ohm represented by Ω
 If the potential difference V is 1 volt and the
current I is 1 ampere, then resistance R is 1 ohm.
 1 ohm = 1 volt/ 1 ampere
 So, 1 ohm is the resistance of a conductor such
that when a potential difference of 1 volt is applied
to its ends, a current of 1 ampere flows through it.

46.  I = V/R
 So,
 The current is directly proportional to pd and
 The current is inversely proportional to resistance.
 Thus if pd is doubled, the current flowing will be
doubled and if pd is halved, the current also gets
halved.
 But current is inversely proportional to resistance,
so if resistance is doubled then current gets halved
and if resistance is halved, then the current gets
doubled.

47.  State Ohm’s Law. How it can be verified
experimentally.
 How much current will an electric bulb draw
from a 220 V source, if the resistance of the
bulb filament is 1200 ohm?
 How much current will an electric heater coil
draw from a 220 V source, if the resistance of
the heater coil is 100 ohm?
 The potential difference between the
terminals of an electric heater is 60V 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.

48.  Potential difference between two points of a
wire carrying 2 ampere current is 0.1 volt.
Calculate the resistance between these
points.
 A current of 5 A is flowing through a resistor
of 15 ohm. Calculate the potential difference
between the ends of the resistor.
 Q 3 of text book pg 209
 Q 8 of text book pg 221