(1) Chiranjeet Samantaray completed an investigatory project on studying the variation of current using a light dependent resistor (LDR) under the guidance of his physics teacher. (2) The project investigated how the current in a circuit containing an LDR varies with changes in the power and distance of an incandescent light source illuminating the LDR. (3) The results showed that the LDR resistance decreases and current increases with higher light intensity from decreasing the distance or increasing the power of the light source.
Study Of oxalte ion in guava fruit at different stages of ripeningPrince Warade
guava is sweet,juicy,light or dark green coulured fruit.we will learn to test for the presence of oxalate ions in the guava fruit and how its amount varies during different stages of ripening.
Physics investigatory project for class 12 on the topic " to estimate charge induced on two styro foam / pith balls separated by a distance "
Just change the name and cover page.
This is the investigatory project on aids. for biology class 12. or can be used for educational purpose. this covers all important topics with good images. if you like this follow me on my instagram @vishal2782003
Class 12 CBSE Biology Investigatory project on the topic "Drug Addiction" which includes the appropriate format and content for the CBSE practical examinations.
TOPIC-To investigate the relation between the ratio of :-1. Input and outpu...CHMURLIDHAR
TOPIC-To investigate the relation between the ratio of :-1. Input and output voltage.2. Number of turnings in the secondary coil and primary coil of a self made transformer.
Study Of oxalte ion in guava fruit at different stages of ripeningPrince Warade
guava is sweet,juicy,light or dark green coulured fruit.we will learn to test for the presence of oxalate ions in the guava fruit and how its amount varies during different stages of ripening.
Physics investigatory project for class 12 on the topic " to estimate charge induced on two styro foam / pith balls separated by a distance "
Just change the name and cover page.
This is the investigatory project on aids. for biology class 12. or can be used for educational purpose. this covers all important topics with good images. if you like this follow me on my instagram @vishal2782003
Class 12 CBSE Biology Investigatory project on the topic "Drug Addiction" which includes the appropriate format and content for the CBSE practical examinations.
TOPIC-To investigate the relation between the ratio of :-1. Input and outpu...CHMURLIDHAR
TOPIC-To investigate the relation between the ratio of :-1. Input and output voltage.2. Number of turnings in the secondary coil and primary coil of a self made transformer.
A Measurements Project on Light Detection sensorsvrohith 9
The main aim of this project is to saving system with LDR this is to save the power. We want to save power automatically instead of doing manual. So it’s easy to cost effectiveness. This saved power can be used in some other cases. So in villages, towns etc. we can design intelligent systems for the usage of light or we can also use this to reduce the electricity bill of our home. This project can also be used for security of the houses, banks, etc.
This paper deals with the Internal quantum efficiency of ITO, CdTe, ZnO/a-Si, SnS/Si, CdS /CIGS, FTO/CZTS based of material photodiode with a ITO/CdTe, ZnO/a-Si, SnS/Si, CdS /CIGS, FTO/CZTS heterojunction structure. Along with information on device characteristics, applications and properties, we provide a comparative device analysis between this type of photodiode and the slightly more efficient ITO/CdTe, ZnO/a-Si, SnS/Si, CdS /CIGS, FTO/CZTS heterojunction structure. We will get the clear concept of the relation between of generated current & load voltage. We hope, we will get a clear explanation about the effect of photodiode light intensity & wavelength on the solar efficiency. In this project we will analyze the Quantum efficiency of a photodiode.
Optical or light related sensors and its principles are discussed. The use of the LDR, photocell, photodiodes, and many more transducers which are based on optical sensors are discussed with the applications related to it.
LDR-experimentation.pdfpg. 1 COVENTRY UNIVERSITY .docxDIPESH30
LDR-experimentation.pdf
pg. 1
COVENTRY UNIVERSITY
Faculty Of Engineering & Computing
AAEE
Light Depended Resistors (LDRs)
Introduction
The light dependent resistor, LDR, is known by many other names such as photoresistor,
photoconductor, photoconductive cell, or simply the photocell. These devices were discovered by an
English electrical engineer Willoughby Smith back in 1873. Smith’s main line of work in 1848 was the
laying of underwater telegraph cables. He developed a method of testing an underwater cable as it
was being laid. One of the insulation materials used for the cable was selenium. Upon investigation
of the properties of the selenium insulator he discovered that the conductivity properties of the
material were affected by light. He published his findings in 1873.
Since then many variants of photoconductive devices have been made. Other LDRs have been made
using materials including cadmium sulphide, lead sulphide, and the more commonly used
semiconductor materials including germanium, silicon and gallium arsenide.
The most popular material used in making LDRs is cadmium sulphide (CdS).
The LDR finds many uses as a low cost photo sensitive element and was used for many years in
photographic light meters as well as in other applications such as lighting controls for street lamps
etc.
Basic structure of an LDR
There are many ways in which light dependent resistors can be manufactured. Essentially the LDR
consists of a resistive material sensitive to light. The photo resistive element comprises section of the
material with contacts at either end. Although many of the materials used for light dependent
resistors are semiconductors, when used as a photo resistor, they are used only as a resistive and
they are purely passive.
A typical structure for a light dependent or photo resistor uses an active semiconductor layer that is
deposited on an insulating substrate. The semiconductor is normally lightly doped to enable it to have
the required level of conductivity. Contacts are then placed either side of the exposed area.
Fig 1 (a,b,c) Close-Up of an LDR (a) Cadmium sulphate (b) and LDR symbol (c)
(a)
(b)
(c)
pg. 2
In many instances the area between the contacts is in the form of a zig zag, or interdigital pattern.
This maximises the exposed area and by keeping the distance between the contacts small it enhances
the gain (see Fig.1 (a).
Although other devices such as photodiodes or photo-transistors can also be used for light sensing
applications, LDRs are a particularly convenient electronic component to use. They provide large
change in resistance for changes in light level. They are of comparatively speaking of a lower cost as
compared to other light responding devices.
How an LDR works
It is relatively easy to understand the basics of how an LDR works without delving into complicated
explanations. It is first necessary to understand that an electrical ...
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Monitor common gases, weather parameters, particulates.
1. i
Acknowledgement
I would like to thank my Physics teacher Mr. R.
Ghadai for his constant guidance, motivation, moral
encouragement and sympathetic attitude towards the
success of this project.
I also want to thank the principal and the institution for
providing the necessary materials.
I would also like to extend my gratitude towards the
lab attendant, my parents and everyone who has
helped me in completing the project successfully.
Chiranjeet Samantaray
Roll. No-
2. ii
Bonafide certificate
This is to certify that Chiranjeet Samantaray of class XII
has successfully completed the investigatory project on
“TO STUDY VARIATION OF CURRENT USING A
LDR" under the guidance of Mr. R. Ghadai.
This project is absolutely genuine and doesn't not
involve in any kind of plagiarism.
This is in partial fulfillment of Physics practical
examination AISSCE 2019-20.
Teacher in ChargeExternal Examiner
Principal School Stamp
3. iii
INDEX
ACKNOWLEDGEMENT i
BONAFIDE CERTIFICATE ii
INTRODUCTION 01
APPLICATIONS
02AIM & APPARATUS
03THEORY
08PROCEDURE
09OBSERVATIONS
11RESULT & CONCLUSION
12
SOURCES OF ERROR 13
BIBLIOGRAPHY 14
4. 1
INTRODUCTION
The general purpose photoconductive cell is also
known as LDR – light dependent resistor. It is a type
of semiconductor and its conductivity changes with
proportional change in the intensity of light.
There are two common types of materials used to
manufacture the photoconductive cells. They
are Cadmium Sulphide (CdS) and Cadmium Selenide
(CdSe).
Extrinsic devices have impurities added, which have
a ground state energy closer to the conduction band -
since the electrons don't have as far to jump, lower
energy photons (i.e. longer wavelengths and lower
frequencies) are sufficient to trigger the device. Two
of its earliest applications were as part of smoke and
fire detection systems and camera light meters. The
structure is covered with glass sheet to protect it from
moisture and dust and allows only light to fall on it.
5. 12
Applications
Lead sulfide (PbS) and indium antimonide (InSb) LDRs
are used for the mid infrared spectral
region. GeCu photoconductors are among the best far-
infrared detectors available, and are used for infrared
astronomy and infrared spectroscopy.
Analog Applications
· Camera Exposure Control
· Auto Slide Focus - dual cell
· Photocopy Machines - density of toner
· Colorimetric Test Equipment
· Densitometer
· Electronic Scales - dual cell
· Automatic Gain Control – modulated light source
· Automated Rear View Mirror
Digital Applications
· Automatic Headlight Dimmer
· Night Light Control
· Oil Burner Flame Out
· Street Light Control
· Position Sensor
*LDR has a disadvantage that when its temperature changes, its
resistance changes drastically for a particular light intensity.
6. 2
AIM & APPARATUS
AIM:
To study the variations, in current flowing in a circuit
containing a LDR, because of a variation:-
(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:
Light Dependent Resistor (LDR)
Connecting Wires
Source of different power rating (bulbs)
Bulb Holder
Metre scale
Multi Meter
Battery
7. 3
THEORY
1.) LDR and its characteristics
When light is incident on it, a photon is absorbed and
thereby it excites an electron from valence band into
conduction band. Due to such new electrons coming up in
conduction band area, the electrical resistance of the
device decreases. Thus the LDR or photo-conductive
transducer has the resistance which is the inverse
function of radiation intensity.
λ0 = threshold wavelength, in meters
e = charge on one electron, in Coulombs
Ew = work function of the metal used, in Ev
Here we must note that any radiation with wavelength
greater than the value obtained in above equation
CANNOT PRODUCE any change in the resistance of this
device.
The band gap energy of Cadmium Sulphide is
2.42eV and for Cadmium Selenide it is1.74eV. Due to
such large energy gaps, both the materials have
extremely high resistivity at room temperature.
8. 4
Characteristics of photoconductive cells
Now when the device is kept in darkness, its resistance
is called as dark resistance. This resistance is typically
of the order of 1013
ohms. When light falls on it, its
resistance decreases up to several kilo ohms or even
hundreds of ohms, depending on the intensity of light,
falling on it.
The spectral response characteristics of two commercial
cells were compared in our laboratory. And we found
that there is almost no response to the radiation of a
wavelength which was shorter than 300nm. It was very
interesting to note that the Cadmium Sulphide cell has a
peak response nearer or within the green color of the
spectrum within a range of 520nm. Thus it can be used
nearer to the infra-red region up to 750nm. It was found
that the maximum response of Cadmium
Sulphoselenide is in the yellow-orange range at 615nm
and also it can be used in the infra-red region up to
about 970nm.
9. Sensitivity
The sensitivity of a photo detector is the relationship
between the light falling on the device and the
resulting output signal. In the case of a photocell,
one is dealing with the relationship between the
incident light and the corresponding resistance of
the cell.
5
10. Spectral Response
Like the human eye, the relative sensitivity of a
photoconductive cell is dependent on the
wavelength (color) of the incident light. Each
photoconductor material type has its own unique
spectral response curve or plot of the relative
response of the photocell versus wavelength of light.
6
11. 2.) luminous flux variation:
Considering the source to be a point radiating in all
directions; consider a steradian (or even a simple
sphere), take a small element dA on the steradian at a
distance ‘r’ from the source. It comprises a small part
of the energy radiated (dEr).
Now, go further to a distance ‘R’ (R>r) from the
source, consider the same area element dA, it
comprises a much smaller part of energy radiated
(dER).
[dEr > dER].
It varies inversely as the square of the distance.
7
12. PROCEDURE
Choose a specific position for the source and mount it
using a holder, make sure it is stable.
Select the bulb with the lowest power rating and connect it
to the holder as shown in the figure.
Connect the LDR, battery(6V) and the multimeter in
series.
Set the multimeter to ohm section and select suitable
range and measure the resistance with a bulb on.
Similarly switch to current section and move to micro
ampere in the multimeter. This gives the value of the
current.
Repeat these steps with different power sources at
different distances and note down observations.
8
13. 9
OBSERVATIONS
The experiment has been conducted by using
various sources with different power ratings.
Voltage of the battery = 6 V
1.) 15 watts (yellow) (wavelength = 570nm)
2.) 15 watts (incandescent) (mean wavelength = 610nm
Serial
No
DISTANCE FROM
SOURCE
(cm)
RESISTANCE
(Kilo ohm)
CURRENT
(micro ampere)
1. 50 142.5 40
2. 40 69 80
3. 30 41 150
4. 20 21 300
Serial
No
DISTANCE FROM
SOURCE
(cm)
RESISTANCE
(Kilo ohm)
CURRENT
(micro ampere)
1. 50 51 120
2. 40 35 170
3. 30 22 270
4. 20 11 540
14. 10
3.) 40 watts (incandescent) (mean wavelength = 610nm)
4.) 20 watts (CFL) (white light)
Serial
No
DISTANCE FROM
SOURCE
(cm)
RESISTANCE
(Kilo ohm)
CURRENT
(micro ampere)
1. 50 20 300
2. 40 13 460
3. 30 8.5 700
4. 20 4.5 1330
Serial
No
DISTANCE FROM
SOURCE
(cm)
RESISTANCE
(Kilo ohm)
CURRENT
(micro ampere)
1. 50 15.5 380
2. 40 10 600
3. 30 6 1000
4. 20 3 2000
15. 11
CONCLUSION & RESULT
The LDR resistance decreases with increase in
intensity of light and hence there is an increase in
the flow of current.
There is an increase in the current as the
distance from the source decreases.
The intensity decreases as the distance from the
source increases
The error lies within the experimental limit.
16. 13
SOURCES OF ERROR
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.
17. 14
BIBLIOGRAPHY
NCERT physics class XII
Art of Electronics by paul worowitz
www.wikipedia.com/
www.electronics2000.co.uk/links/education-hobby/
www.ecelab.com/
laboratory manual in physics
Practical physics