2.  A continuous conducting path consisting of wires and other
resistance (like Bulb) and a switch, between the two terminals of a
cell or a battery along with an the electric current flows, is called an
electric circuit.
 An electric current is a flow of electric charge. Electric charge flows
when there is voltage present across a conductor.
 In electric circuits this charge is often carried by moving electrons in
a wire.
 The SI unit for measuring an electric current is the ampere, which is
the flow of electric charges through a surface at the rate of one
coulomb per second. I=Q/T
 Electric current can be measured using an ammeter.
 The conventional symbol for current is (I) .

3. Potential Difference
 Potential Difference (p.d) between two point s in an
electric circuit is defined as the work done in moving a
unit charge from one point to the other point.
 It is represented by the symbol ‘V’.
 Potential difference= Work done/Quantity of charge
moved V=W/Q
 1V=1W/1C
 The p.d is measured by an means of an instrument
called voltmeter. It has a high resistance so that it
takes negligible current from the circuit.
 It is connected parallel to the circuit.

4. Common symbols used in a circuit diagram

5.  Ohm's law states that the current through a
conductor between two points is directly proportional to the
potential difference across the two points at a constant temperature.
 Introducing the constant of proportionality, the resistance, one
arrives at the usual mathematical equation that describes this
relationship: V=IR
 I∝V ; V∝I ; I=V/R
 If p.d across the ends of a conductor is doubled then the I also
doubles & if the p.d is halved then the current also becomes half.
 If the resistance is doubled then the current gets halved, and if the
resistance is halved the current gets doubled.
 It is represented by a symbol omega, Ω.
 V-I graph is a straight line graph.

6.  Electric resistance of a conductor depends on the following factors:
 Effect of length of the conductor
 Effect of area of cross –Section of the conductor
 Effect of nature of material of the conductor
 Effect of temperature

7. Resistivity
Derive the formula for resistivity:
 R∝l –(1) ; R∝1/A–(2)
From (1) &(2)
R∝l/A; R=𝜌𝐿/𝐴; where 𝜌(𝑟ℎ𝑜)
 𝜌 =
RA
L
 The resistivity of a substance is numerically equal
to the resistance of a rod of that substance which
is 1 metre long
and 1 metre in cross section.
 𝜌 = 𝑜ℎ𝑚 × 𝑚𝑒𝑡𝑟𝑒 2/metre

8.  The resistivity of a substance does not depends upon its length &
thickness.
 It depends on the nature & the temperature.
 Good conductors of electricity have low resistivity and a poor
conductor has high resistivity.
 Silver has the lowest resistivity, which means that silver offers the
least resistance to the flow of current through it.
 The resistivities of alloys are much higher than those of pure metals
(from which they are made).
 The resistivity of semi-conductor like silicon is in-between those of
conductors and insulators, and decreases on ≤temp.

10.  When resistances are connected in series then the total resistances is:
 Req =R1 +R2 +R3 +….+Rn
 Disadvantages of series combination:
1. In series circuit, if one appliance stops working due to some defect, then all
other appliances also stop working because the whole circuit is broken.
2. In series circuit, all the appliances have only one switch due to which they
cannot be turned on or off separately.
3. In series circuit, the appliances do not get the same voltage (220V) as that of
the power supply because the voltage is shared by all the appliances because
the voltage is shared by the appliances. The appliances get less voltage and do
not work properly.
4. In the series connection of electric appliances, the overall resistances of the
circuit increase too much due to which the current from the power supply is
low.

11.  When resistances are connected in parallel then the total
resistances is:
 Advantages of parallel combination are:
1. In a parallel circuit, if one electrical appliance stops working due to some defect
then all the other appliance keeps working normally.
2. In a parallel circuit , each electric appliance has its own switch due to which it can
be turned on and off independently, without affecting the other appliances .
3. In a parallel circuit , each electric appliance gets the same voltage (220V) as that
of the power supply line. Due to this all appliance will work properly
4. In the parallel connection of electrical appliances, the overall resistance of the
household circuit is reduced due to which the current from the power supply line
is high.

12.  Electric power is the electric work done per unit time.
 Power =𝑊𝑜𝑟𝑘 𝐷𝑜𝑛𝑒 𝑇𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 : P=W/t
 SI unit of electric power is Watt (W).
 The power of 1 watt is a rate of working of 1Joule per second.
 Other formulae: P=V×I -(1)
 Electric power =p.d×Current
 1W= 1Volt×1 Ampere
 By Ohms law P=I2×R -(2)
 P in terms of V and R P=V2/R -(3)
 Power is inversely proportional to the resistance.
 Commercial unit of Power is Kilowatt-hour.

13.  When an electric current is passed through a high resistance wire, like
Nichrome, the resistance wire becomes very hot and produces heat. This
is called the Heating Effect Of Electric current.
 It is obtained by the transformation of electric energy into heat energy
 H=I2×R × t implies that the heat produced in a wire is directly
proportional to : square of current; resistance of wire ; Time…
 Applications: 1.Heating effect of electric current is used in bulbs to
produce light.
 It is utilized in electric fuse for protecting household wiring and electrical
appliances.
 It is utilized in the working of electrical heating appliances such as
electric iron, Kettle, toaster and many more….

14. Made By: Vivek sharma
Of :X-B
Roll No.-17