1) Electricity is a form of energy that can be produced from other types of energy like chemical reactions or mechanical rotation. It has advantages like being clean, flexible, efficient, and allowing for easier transmission. 2) An electric circuit consists of a power source, load, switches, and other elements connected by wires. Resistors, rheostats, and resistance boxes in a circuit are made of materials like manganin and constantan. 3) Ohm's law states that the current through a conductor is directly proportional to the potential difference across it, provided the physical conditions stay the same. The resistance of a conductor depends on its length, cross-sectional area, and the material it is

1. Pritish Dixit
Roll No- 25

2. Electricity
 Electricity is one of the forms of energy and it can be
produced from other types of energy, such as the energy
of a chemical reaction or of mechanical rotation of
dynamo.
 Its great advantages are:
> cleanness
> flexibility
> efficiency
> easier transmission

3. Electric Circuit
 A source of electric power ( a battery or an AC
source), load and switches and other elements
connected together by wires form an electric circuit .

4.  Resistors, Rheostats and Resistance Boxes consist of wires
which are generally made of alloys such as manganin and
constantan.
VARIABLE RESISTOR
RESISTOR
RHEOSTAT
R
RESISTANCE BOX

5. OHM’S LAW
 Ohm’s Law states that if physical conditions like temperature
etc., of a conductor are kept unchanged, the strength of
current flowing through it is directly proportional to the
potential difference across the ends.
 If V=potential difference across the ends of a conductor
I=strength of the current flowing through the conductor
According to ohm’s law,
or V=RI
where R is a constant of proportionality whose value
depends on size, nature of the material and temperature of
the conductor.

6. RESISTANCE
 The resistance of a conductor is the ratio of the potential
difference across its ends to the strength of the strength
of the current flowing through it.
 Resistance =
 Unit of resistance: The SI unit is the practical unit of
resistance and is called ohm. It is represented by the
symbol Ω.

7. Factors on which resistance depends
 Length(l). If the length of the conductor increases, the
electrons have to travel a longer distance and as a result
of this, its resistance increases.
 Cross-sectional area (A).If the cross-sectional area of the
conductor decreases, the electrons find it more difficult
to pass through it and resistance increases.
where is a constant of proportionality and is called is
called resistivity.

9. Combination of resistors in series
 A number of resistors are said to be connected in series if
these are joined end to end and the same current flows
through each of them when a potential difference is
applied across the combination.
 In series combination, the equivalent resistance is equal
to the sum of individual resistances and is greater than
any individual resistance.

10.  Let us consider a circuit in which three resistors R1, R2 and R3 are connected in
series with a battery of potential difference V. The potential difference V is equal
to the sum of potential differences V1, V2, and V3. That is the total potential
difference across a combination of resistors in series is equal to the sum of
potential difference across the individual resistors. That is,
V = V1 + V2 + V3 ------------ (i)
 Applying the Ohm’s law to the entire circuit,
V = I Rs. ------------------- (ii)
On applying Ohm’s law to the three resistors separately,
V1 = I R1; V2 = I R2; and V3 = I R3. ------------------- (iii)
From the equations (i ),(ii) and (iii)
I Rs = I R1 + I R2 + I R3 implies that
Rs = R1 +R2 + R3.

11. Combination of resistors in parallel
 A number of resistors are said to be connected in parallel if
one end of each resistor is connected to one point and the
other end is connected to another point so that the
potential difference across each resistor is the same and is
equal to the applied potential difference between the two
points.
 In parallel combination, the reciprocal of the equivalent
resistance is equal to the sum of the reciprocals of the
individual resistances and is smaller than any individual
resistance.

12.  Consider the arrangement of three resistors joined in parallel with a battery. It is
observed that the total current I, is equal to the sum of the separate currents
through each branch of the combination.
I = I1 + I2 + I3 --------------- (i)
 On applying Ohm’s law to each resistor,
I1 = V/R1 ; I2 = V/R2 ; and I3 = V/R3 --------------- (iii)
From the equations (i), (ii) and (iii)
V/Rp = V/R1 + V/R2 + V/R3
or 1/Rp = 1/R1 + 1/R2 + 1/R3 .