Light LDR to study current depends
Physics
23 pag.
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Physics Investigatory
Project
11/25/2016
LIGHT
DEPENDE
NT
RESISTOR
Submitted by
Gopi Nath Sah
Class XII A
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Acknowledgement
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I would like to express my
special thanks of gratitude to
my teacher (Mrs. Alka Chopra)
as well as our principal (R K
Tyagi) who gave me the golden
opportunity to do this
wonderful project on the topic
(Write the topic name), which
also helped me in doing a lot of
Research and i came to know
about so many new things I am
really thankful to them.
Secondly I would also like to
thank my parents and friends
who helped me a lot in finalizing
this project within the limited
time frame.
Gopi Nath Sah
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Bonafide certificate
This is to certify that Gopi Nath Sah of
class XII A has successfully completed the
investigatory project on “TO STUDY
VARIATION OF CURRENT USING A LDR"
under
the guidance of Mrs. Alka
Chopra .This project is absolutely genuine
and doesn't not involve in any kind of
plagiarism. This is in partial fulfillment of
Physics practical examination CBSE 2016.
Department of
Physics
(Mrs Alka
Chopra)
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ACKNOWLEDGEMENT
BONAFIDE CERTIFICATE
i.
ii.
1. INTRODUCTION
2
2. AIM & APPARATUS
3
3. PHOTORESISTOR DISCOVERY
AND MECHANISM
4. PRINCIPLE & THEORY
4-5
5-6
5. BRIEF DESCRIPTION OF
COMPONENTS
6. APPLICATIONS
6-8
9
7. PROCEDURE
10
8. OBSERVATIONS
11-14
9. RESULT & CONCLUSIONS
10. BIBLOGRAPHY
15
16
INDEX
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LIGHT DEPENDENT RESISTANCE
Project Report Physics
INTRODUCTION
In the society, sometimes street lights glow in
day time due to any reason. In mines area people
face many difficulties due to absence of light in
the nights. In frontier and hilly areas, people face
many problems due to damaged street lights.
For solve above these problems, we create a
device in which the lights glow in night and in
day time, they off automatically and don't glow.
Due to use of it, we can solve above problems
and can also save electricity and men's power.
AIM: To study the variations, in current flowing
in a circuit
a variation:-
containing
a
LDR,
because of
(a) In the power of the incandescent lamp, used
to ‘illuminate’ the LDR. (Keeping all the lamps at
a fixed distance).
(b) In the distance of a incandescent lamp, (of
fixed power), used to ‘illuminate’ the LDR.
APPARATUS:
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Light Dependent Resistor(LDR),Connecting Wires,
Source of different power rating(bulbs), Bulb
Holder , Metre scale, Multi Meter Battery.
Photo
discovery
resistor
Photo resistors, or light dependent
resistors have been in use for very
many years. Photo resistors have
been seen in early forms since the
nineteenth
century
when
photoconductivity in selenium was
discovered by Smith in 1873. Since
then
many
variants
of
photoconductive devices have been
made.
Much useful work was conducted by
T. W. Case in 1920 when he published
a paper entitled "Thalofide Cell - a
new photo-electric cell".
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Other substances including PbS, PbSe
and PbTe were studied in the 1930s
and 1940s, and then in 1952, Rollin
and
Simmons
developed
their
photoconductors using silicon and
germanium.
Photoresistor mechanism
A photoresistor or photocell is a component that uses a
photoconductor between two contacts. When this is exposed to
light a change in resistance is noted. Photoconductivity - the
mechanism behind the photoresistor - results from the
generation of mobile carriers when photons are absorbed by
the semiconductor material used for the photoconductor. While
the different types of material used for light dependent resistors
are semiconductors, when used as a photo-resistor, they are
used only as a resistive element and there are no PN junctions.
Accordingly the device is purely passive.
There are two
photoresistor:
types
of
photoconductor
and
hence
 Intrinsic photoresistor: This type of photoresistor
uses a photoconductive material that involves excitation of
charge carriers from the valence bands to the conduction
band.
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 Extrinsic photoresistor: This type of photoresistor
uses a photoconductive material that involves excitation of
charge carriers between an impurity and the valence band
or conduction band. It requires shallow impurity dopants
that are not ionised in the presence of light.
 Extrinisc photoresistors or photocells are generally
designed for long wavelength radiation - often infra-red, but
to avoid thermal generation they need to be operated at
low temperatures.
PRINCIPLE
This project is based on Light Dependent Resistance
(L.D.R.). Light Dependent Resistance [LDR] is a resistance, in
which opposing power of current depends on the presence of
quantity of light present, i.e. the resistance of LDR increases or
decreases, according to quantity of light which falls on it.
If LDR places in darkness, the resistance of LDR increases and
when light falls on it, the resistance of LDR decreases and act
as a conductor. Any LDR in the presence of light and darkness
changes its resistance is depends on the different types of LDR.
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ADVANTAGES
 Collection of parts of the circuit are easily available.
 Accuracy of this circuit is more than accuracy of other
circuits.
 By using laser, it can be used for security purposes.
 It can be used to stop the wastage of electricity.
 The cost of circuit is low.
 This circuit saves the men's power.
USES







It can be used in street lights.
It can be used in mines areas.
It can be used in hilly areas.
By using laser, it can be used for safety purposes.
It can be used in frontier areas.
It can be used in houses.
It can be used in jail lights.
BRIEF DISCRIPTION OF COM PONENTS
1. TRANSISTOR:-When a thin slice of p-type is sandwiched
between two blocks of n-type, then n-p-n transistor is formed. It
consists of emitter, base, and collector. In the project, common emitter
n-p-n transistor ( BC-147 & SL-100) is used.
2. DIODE:- When a p-type and n-type semiconductors are joined a
diode is formed. It conducts when forward biased and does not
conduct when reverse biased. In the project, IN-4007diode is used.
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3. RELAY:- It helps to contact and discontact. In the project, we use
relay of 6 ohms.
4. CARBON RESISTOR:- A carbon resistor has generally four rings
or bands A,B,C and D of different colours corresponding to the value
of resistance. In project, we use carbon resistance of 220 kilo-ohms,
1.5 kilo-ohms and 820 ohms.
5. LDR:- LDR means light dependent resistance which is used to
complete the circuit.
6. TRANSFORMER:- Transformer is
used to convert low alternating voltage Photoresistor
to high alternating voltage by
decreasing the current and vice-versa.
We use a transformer of 6-0-6V for the
circuit.
7. CAPACITOR:- Capacitor is used to
block DC. In the circuit, we use the
capacitor of 220mfd and 1000mfd.
8.BULB:- An electric bulb is connected
to the circuit when LDR comes in the
darkness.
9.PHOTORESISTORA photoresistor (or lightdependent
resistor, LDR,
or photocell) is a light-controlled
variable resistor. The resistance of
a photoresistor decreases with
increasing incident light intensity; in
other
words,
it
Type
Passive
Working Photoconductivity
principle
Electronic symbol
The
symbol
photoresistor
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a
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exhibits photoconductivity. A photoresistor can be applied in
light-sensitive detector circuits, and light- and dark-activated
switching circuits.
A photoresistor is made of a high resistance semiconductor. In
the dark, a photoresistor can have a resistance as high as
several megohms (MΩ), while in the light, a photoresistor canΩ), while in the light, a photoresistor can), while in the light, a photoresistor can
have a resistance as low as a few hundred ohms. If incident
light
on
a
photoresistor
exceeds
a
certain frequency, photons absorbed by the semiconductor give
bound electrons enough energy to jump into the conduction
band. The resulting free electrons (and their hole partners)
conduct electricity, thereby lowering resistance. The resistance
range and sensitivity of a photoresistor can substantially differ
among dissimilar devices. MΩ), while in the light, a photoresistor canoreover, unique photoresistors may
react substantially differently to photons within certain
wavelength bands.
A photoelectric device can be either intrinsic or extrinsic. An
intrinsic semiconductor has its own charge carriers and is not
an efficient semiconductor, for example, silicon. In intrinsic
devices the only available electrons are in the valence band,
and hence the photon must have enough energy to excite the
electron across the entire band gap. Extrinsic devices have
impurities, also called dopants, added whose ground state
energy is closer to the conduction band; since the electrons do
not have as far to jump, lower energy photons (that is, longer
wavelengths and lower frequencies) are sufficient to trigger the
device. If a sample of silicon has some of its atoms replaced by
phosphorus atoms (impurities), there will be extra electrons
available for conduction. This is an example of an extrinsic
semiconductor.
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Applications
The internal components of a photoelectric control for a typical
American streetlight. The photoresistor is facing rightwards, and
controls whether current flows through the heater which opens
the main power contacts. At night, the heater cools, closing the
power contacts, energizing the street light.
Photoresistors come in many types. Inexpensive cadmium
sulphide cells can be found in many consumer items such as
camera light meters, clock radios, alarm devices (as the
detector for a light beam), nightlights, outdoor clocks, solar
street lamps and solar road studs, etc.
Photoresistors can be placed in streetlights to control when the
light is on. Ambient light falling on the photoresistor causes the
streetlight to turn off. Thus energy is saved by ensuring the light
is only on during hours of darkness.
They are also used in some dynamic compressors together with
a small incandescent or neon lamp, or light-emitting diode to
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control gain reduction. A common usage of this application can
be found in many guitar amplifiers that incorporate an
onboard tremolo effect, as the oscillating light patterns control
the level of signal running through the amp circuit.
The use of CdS and CdSe[3] photoresistors is severely restricted
in Europe due to the RoHS ban on cadmium.
Lead sulphide (PbS) and indium antimonide (InSb) LDRs (lightdependent resistors) are used for the mid-infrared spectral
region. Ge:Cu photoconductors are among the best farinfrared detectors available, and are used for infrared
astronomy and infrared spectroscopy.
PROCEDURE
1.
Choose a specific position for the
source and mount it using a holder,
make sure it is stable.
2.
Select the bulb with the lowest
power rating and connect it to the
holder as shown in the figure.
3.
Connect the LDR, battery (6V) and
the multimeter in series.
4.
Set the multimeter to ohm section
and select suitable range and measure
the resistance with a bulb on.
5.
Similarly switch to current section
and move to micro ampere in the
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multimeter. This gives the value of the
current.
6.
Repeat these steps with different
power sources at different distances
and note down observations.
OBSERVATIONS :The experiment has been conducted by using various sources with
different power ratings. Voltage of the battery = 6 V.
OBSERVATIONS TABLE :(a) Variation in current of LDR with lamps of different power,
keeping distance fixed.
S.No.
Distance
between
LDR and
Source(Bulb Resistance(Ω ) Current(mA)
)
Of power
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the source
d(cm)
imputs(W)
1.
10
15
1310
4.58
2.
10
30
770
7.00
3.
10
60
285
21.00
4.
10
100
195
30.00
1.
20
15
2800
2.14
2.
20
60
650
9.00
3.
20
100
435
13.79
1.
30
15
4300
1.4
2.
30
60
1000
6.00
3.
30
100
660
9.00
(b) Variation in current of LDR with distance :-
FOR 15 W POWER SOURCE
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S.No.
Distance between
LDR and the Resistance(Ω )
source d(cm)
Current(µA)
1.
4
1010
5.94
2.
6
1350
4.44
3.
8
1490
4.03
4.
10
1610
3.73
5.
12
1740
3.45
6.
14
1880
3.19
7.
16
2300
2.61
8.
18
2540
2.36
9.
20
2800
2.14
10.
22
3000
2.00
11.
24
3240
1.85
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FOR 60 W POWER SOURCE
Distance between
S.No
LDR and the Resistance(Ω )
.
source d(cm)
Current(mA)
1.
4
105
57
2.
6
180
33
3.
8
230
26
4.
10
280
21
5.
12
360
16
6.
14
440
13
7.
16
500
12
8.
18
575
10
9.
20
675
8.8
10.
22
740
8.1
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11.
24
820
7.3
FOR 100 W POWER SOURCE
Distance between
S.No
LDR and the Resistance(Ω )
.
source d(cm)
Current(mA)
1.
4
80
75
2.
6
130
46
3.
8
170
35
4.
10
205
29
5.
12
270
22
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6.
14
300
20
7.
16
360
16
8.
18
410
14
9.
20
460
13
10.
22
525
11
11.
24
585
10
CONCLUSION & RESULT
1. The LDR resistance decreases with increase in intensity of light
and hence there is an increase in the flow of current.
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2. There is an increase in the current as the distance from the
source decreases.
3. The intensity decreases as the distance from the source
increases
4. The error lies within the experimental limit.
SOURCES OF ERROR
1.
2.
3.
4.
The LDR may not be perpendicular to the source.
Connections may be faulty.
The experiment should be conducted in a dark room.
Measurements should be taken accurately.
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Biblography
1. NCERT CLASS 12 PHYSICS TEXTBOOK
2. www.google.co.in
3. www.wikipedia.com
4. www.yahoo.co.in
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