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ACKNOWLEDGEMENT I would like to thank my physics teacher Mrs. SUNITA SUNITA SHARMA for her constant guidance moti!ation moral encouragement and sympathetic attitude towards towards the success of this pro"ect. I also want to thank the principal and the institution for pro!iding the necessary materials. I would also like to e#tend my gratitude towards the la$ attendant my parents and e!eryone who has helped me in completing the pro"ect successfully.
CHAITANYA NIRGULE
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KEND KE NDRIY RIYA A
VID VI DYAL ALA AYA
ONGC ON GC
PANVEL
BONAFIDE
CERTIFICATE
This is to certify that &HAITAN'A NIR(U)* of class +II has successfully completed the in!estigatory pro"ect on ,T- STU' /ARIATI-N -0 &URR*NT USIN( A )R1 under the guidance of Mrs.sunita sharma. uring year 23%4 5 23%6 Roll No.
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Internal Signature
7rinciple
*#ternal Signature
TO STUD STUDY Y VARIATION VARIATION OF CURRENT USING A LDR
INTRODUCTION The The gene genera rall purp purpos ose e phot photoc ocon ondu duct cti! i!e e cell cell is also also known as )R < light dependent resistor. It is a type of semiconductor and its conducti!ity changes with proportional change in the intensity of light. There are two common types of materials used to manu manufa fact ctur ure e the the phot photoc ocon ondu duct cti! i!e e cell cells. s. They hey are are Cadmi admium um Sulph ulphid ide e (CdS (CdS)) and Cadmiu Cadmium m Seleni Selenide de (CdSe). *#trinsic de!ices ha!e impurities added which ha!e a ground state energy closer to the conduction $and since the electrons don=t ha!e as far to "ump lower energy photons >i.e. longer wa!elengths and lower fre?uencies@ are sufficient to trigger the de!ice. Two of its earliest applications were as part of smoke and fire detection systems and camera light meters. The structure is co!ered with glass sheet to protect it from moisture and dust and allows only light to fall on it.
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APPLICATIONS )ead sulfide >7$S@ and indium antimonide >InS$@ )Rs are used for the mid infrared spectral region. (e&u are are used for infrared infrared astronomy and infrared spectroscopy. Analog Applications &amera *#posure &ontrol Auto Slide 0ocus 5 dual cell 7hotocopy Machines 5 density of toner &olorimetric &olorim etric Test *?uipment *?uipme nt ensitometer *lectronic Scales 5 dual cell Automatic Automatic (ain &ontrol < modulated light source Automated Rear /iew Mirror Digital Applications Automatic Automatic Headlight immer Night )ight &ontrol -il 9urner 0lame -ut Street )ight &ontrol 7osition Sensor
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AIM & APPARATUS AIMB To study the !ariations in current flowing in a circuit containing a )R $ecause of a !ariationB5 >a@ In the power of the incandescent lamp used to CilluminateD the )R. >Eeeping all the lamps at a fi#ed distance@. >$@ >$@ In the distance of a incande ndescent lamp mp >of fi#ed power@ used to CilluminateD the )R. A77A A77ARATU RATUSB SB )ight ependent Resistor >)R@ &onnecting Fires Source of different power rating >$ul$s@ 9ul$ Holder Metre scale Multi Meter
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THEORY %.@ LDR and its characteristics Fhen light is incident on it a photon is a$sor$ed and ther there$ e$y y it e#ci e#cite tes s an elec electr tron on from from !ale !alenc nce e $and $and into into conduction $and. ue to such new electrons coming up in condu conduct ctio ion n $and $and area area the the elec electr tric ical al resi resist stan ance ce of the the de!i de!ice ce decr decrea ease ses. s. Thus Thus the the )R )R or phot photo5 o5co cond nduc ucti ti!e !e transducer has the resistance which is the in!erse function of radiation intensity.
G3 threshold wa!elength in meters e charge on one electron in &oulom$s *w work function of the metal used in *!
Here we must note that any radiation with wa!elength greater ter than the !alu alue o$tained ned in a$o!e e?ua ?uation &ANN-T 7R-U&* any change in the resistance of this de! de!ice. ice.Th The e $and $and gap gap ener energy gy of Cadm Cadmiu ium m Sulp Sulphi hide de is 2.;2e/ and for Cadm Cadmiu ium m Sele Seleni nide de it is%.6;e/. is%.6;e/. ue to such large energy gaps $oth the materials ha!e e#tremely high resisti!ity at room temperature. ;
Characteristics of photoconductive cells Now when the de!ice is kept in darkness its resistance is called as dark resistance. This resistance is typically of the order of %3%: ohms. ms. Fhen light falls on it its resistance decreases up to se!eral kilo ohms or e!en hundreds of ohms depending on the intensity of light falling on it. The spectral response characteristics of two commercial cells were compared in our la$oratory. And we found that there is almost no response to the radiation of a wa!elength which was shorter than :33nm. It was very interesting to note that the &admium Sulphide cell has a peak response nearer or within the green color of the spectrum within a range of 23nm. Thus it can $e used nearer to the infra5red region up to 63nm. It was found that the ma#imum response of &admium Sulphoselenide is in the yellow5orange range at 4%nm and also it can $e used in the infra5red region up to a$out J63nm. Sensitivity The sensiti!ity of a photo detector is the relationship $etween the light ght falling on the de!ice and the resulting output signal. In the case of a photocell one one is deal dealin ing g with with the the rela relati tion onsh ship ip $etw $etwee een n the the
incident light and the corresponding resistance of the cell.
Spectral Response )ike )ike the the huma human n eye eye the the rela relati ti!e !e sens sensit itii!ity !ity of a photoconducti!e cell is dependent on the wa!elength >color@ of the incident light. *ach phot photoc ocon ondu duct ctor or mate materi rial al type type has has its its own own uni? uni?ue ue spectra tral response cur!e r!e or plot of the relati!e response of the photocell !ersus wa!elength of light.
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2.@ luminous flux variation: &onsidering the source to $e a point radiating in all directionsK consider a steradian >or e!en a simple sphere@ take a small element d A A on the steradian at a distance CrD from the source. It comprises a small part of the energy radiated > d*r@. Now go further to a distance CRD >RLr@ from the source consider the same area element d A A it comprises a much smaller part of energy radiated >d*R@.
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PROCEDURE
&hoose a specific position for the source and mount it using a holder make sure it is sta$le. Select the $ul$ with the lowest power rating and connect it to the holder as shown in the figure. &onnect the )R $attery>4/@ and the multimeter in series. Set Set the the mult multim imet eter er to ohm ohm sect sectio ion n and and sele select ct suit suita$ a$le le range and measure the resistance with a $ul$ on. Simi Simila larly rly swit switch ch to curr curren entt sect sectio ion n and and mo!e mo!e to micr micro o ampe ampere re in the the mult multim imet eter er.. This This gi!e gi!es s the the !alue alue of the the current. Repea epeatt thes these e steps eps with ith diff ifferen erentt pow power sourc ources es at different distances and note down o$ser!ations.
OBSERVATIONS The e#perimen ment has $een conducted $y using !ario rious sources with differen rent power ratings. /oltage /oltage of the $attery 4 /
%.@ % watts >yellow@ >wa!elength 63nm@ Serial No
ISTAN&* 0R-M S-UR&* >cm@
R*SISTAN&* >Eilo ohm@
&URR*NT >micro ampere@
%.
3
%;2.
;3
2.
;3
4J
3
:.
:3
;%
%3
;.
23
2%
:33
2.@ % watts >incandescent@ >mean wa!elength 4%3nm Serial No
ISTAN&* 0R-M S-UR&* >cm@
R*SISTAN&* >Eilo ohm@
&URR*NT >micro ampere@
%.
3
%
%23
2.
;3
:
%63
:.
:3
22
263
;.
23
%%
;3
:.@ ;3 watts >incandescent@ >mean wa!elength 4%3nm@ Serial No
ISTAN&* 0R-M S-UR&* >cm@
R*SISTAN&* >Eilo ohm@
&URR*NT >micro ampere@
%.
3
23
:33
J
2.
;3
%:
;43
:.
:3
.
633
;.
23
;.
%::3
;.@ 23 watts >&0)@ >white light@ Serial No
ISTAN&* 0R-M S-UR&* >cm@
R*SISTAN&* >Eilo ohm@
&URR*NT >micro ampere@
%.
3
%.
:3
2.
;3
%3
433
:.
:3
4
%333
;.
23
:
2333
CONCLUSION CON CLUSION & RESU RESUL LT
The )R resistance decreases with increase in intensity of light and hence there is an increase in the flow of current. There is an increase increase in the current as the distance distance from the source decreases. The intensity decreases as the distance from the source increases The error lies within the e#perimental limit.
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SOURCES OF ERROR
The )R may not $e perpendicular to the source.
&onnections may $e faulty. faulty.
The e#periment should $e conducted in a dark room.
Measurements should $e taken accurately.
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BIBLIOGRAPHY
N&*RT physics class +II Art of *lectronics $y paul worowitO
