Physics

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RESISTANCE IN SERIES

at components in such a way that the current has to
force its way first through R1 and then through R2.
This is known as a series circuit.

If R1 is 100k ohm and R2 is also 100k ohm then total
value is 200k ohm. Since the current has to force its
way through first one resistor and then the other, this
combining of the two values to produce an effective
value equal to their sum is really what one would
expect. In fact the total resistance of a series resistor
circuit is always equal to the sum of the resistor
values, regardless of the number of resistor present
in the circuit.

This can be expressed by the equation
RT = R1 + R2 + R3 + R4 +…………
where RT is the total resistance and R1, R2, R3 etc.
are the individual resistance values in the circuit.
RESISTANCE IN PARALLEL
If the two resistances connected across the each
other then we say they are connected in parallel.

If two 200kilo ohm resistances connected in parallel
then total combined value is 100kilo ohm.

The equation for calculating the combined resistance
of a parallel resistance is

1/RT = 1/R1 + 1/R2 + 1/R3 +………

If we take a simple example, say two 8ohm resistors
and one 4ohm resistor in parallel. This gives
1      =         1          =   1 = 2ohm
1/8+1/8+1/4       0.125+0.125+0.25     0.5

One would expect the combined resistance of circuit
is less than the value of lowest resistance connected
in parallel. If 100 ohm and 100 k ohm resistance
connected in parallel then total value is less than
100ohm.
CIRCUIT WORKING
In this model we show the working of resistance in series
and parallel circuit with the help of Dc bulb. Here we use 3
volt Dc battery and few resistances. We use one 470 ohm
resistance in single and two 470 ohm is series circuit and
two 470 ohm in parallel circuit.

We use one L.E.D. with connecting probe to check the flow
of current through resistance. If resistance is more, then
output current is low and light of L.E.D. is also dim.

We check the light of L.E.D. through three combinations.
1. Single 470 ohm resistance.
2. 470 ohms resistances in series.
3. 470 ohms resistances in parallel.

Two 470 ohms in series becomes 940 ohm.

Two 470 ohms in parallel becomes 235 ohm.

Intensity of light in parallel circuit is much higher than the
other two circuits.

If we use voltmeter in place of L.E.D. Then we see the
actual position of the voltage drop in the series and
parallel circuit.
COMPONENTS DETAILS

1.L.E.D.

2.RESISTANCE (470 ohm)

3.BATTERY

4. CONNECTED WIRE
Resistor is an electronics component whose
resistance value tells us about the opposition it
offers to the flow of electrical current. Resistance is
measured in ohms, kilo-ohm and mega-ohm.

Mega ohm = 1000 K ohm = 1000 000 ohm.

TYPES OF RESISTORS
Carbon composition, carbon film metal film and wire
wound resistor’s are the popular types of fixed
resistors. In carbon film resistors, the resistive
element is a relatively thin layer of carbon film
painted or deposited on a ceramic or glass tube.
These are usually available in the resistance range of
1ohm to 100ohm and percentage tolerance
specification of +5%, +2%, +1% and +0.5%. In
metal film resistors, the resistive element is a film of
metal, metal alloy or metal oxide. In wire wound
resistor’s the resistive element is a length of wire
wound in one or more than one layers on an
insulating case.
IMPORTANT RESISTOR SPECIFICATIONS

Resistance Value, Percentage Tolerance and
Wattage Rating are the more popular
specifications of fixed resistors. For all practical
purposes a resistor is almost a completely defined
with these three specifications. Less common
specifications include the voltage rating, the
temperature co-efficient of resistance and voltage
co-efficient of resistance.

It is expressed in ohms, kilo-ohms or mega-ohms.
Tolerance of a resistor is the permissible plus or
minus deviation in the resistance value. Metal film
resistor offers only 1% tolerance, carbon
resistance offer 5% to 10% tolerance. Wattage
rating of a resistor should be so chosen that it be
about twice the power that is likely to be dissipated
when used in the circuit.
CIRCUIT DIAGRAM
INTRODUCTION

RESISTANCE IN SERIES AND PARALLEL

Resistances are used to limit the current in circuits.
How well a material conducts electricity in termed
conductance but it is more normal to measure the
ability of a conductor in terms of how much it
opposes a current flow rather than how easily it
permits a current flow. The opposition to a current
flow is termed resistance and it is measured in
Ohms.

OHM’S LAW

Ohm’s law gives an exact mathematical
relationship between resistances, current, voltage.
If quantities for any two of these are known, a
quantity for the third can be calculated.
OHM’S Law is
AIM

RESISTANCE IN SERIES

AND PARALLEL
This is to certify that PRADEEP of XII-B
Roll No 6669512
Rao Tula Ram Govt. Sarvodya Vidhyalya,
Surhera, New Delhi

CERTIFICATE
has worked under my supervision on the project

RESISTANCE IN SERIES

AND PARALLEL”

The project has been successfully completed and
submitted her under my guidance.
ACKNOWLEDGEMENT

It is my duty to record my sincere thanks
and deep sense of gratitude to my
respected teacher ……….………………
for her valuable guidance, interest and
constant     encouragement      for   the
fulfillment of the project.

I am also highly obliged to our Lab
Teacher ……………..who provided me
the required apparatus and materials.