Part of Made in India,Design Innovation

Workshop,2015

A  Fresh  New  Experience  in  Project-­‐Making  &  Learning!

PHYSICS INVESTIGATORY PROJECT ON

LDR AS VARIABLE RESISTOR

Have  you  seen  the  Volkswagen’s  talking  newspaper  ad?    An  LDR  (light  dependant  resistor)  was  embedded  in  the  newspaper  such  that  the  moment  a  person  opened  the  newspaper,  light  fell  on  the  LDR  and  the  audio  circuit  became  acMve,  producing  a  pre-­‐recorded  sound.

In  this  project,  you  will  need  a  breadboard,  an  LED,  a  resistor,  an  LDR,  a  mulMmeter  and  a  few  connecMng  wires.  A  mulMmeter  is  connected  in  series  with  the  circuit.  When  the  light  is  switched  off,  the  current  in  the  circuit  and  the  resistance  across  the  LDR  were  measured  through  the  mulMmeter.  The  value  of  current  was  also  calculated  theoreMcally  using  Ohm’s  law  and  KVL  (Kirchhoff’s  Voltage  Law).  Both  values  were  found  to  be  approximately  the  same.

Then  the  same  circuit  was  observed  in  light,  and  likewise  the  current  and  resistance  were  measured.  In  this  case  also,  both  the  theoreMcal  and  mulMmeter  values  of  current  were  found  to  be  approximately  the  same.  However,  it  was  observed  that  the  resistance  offered  by  the  LDR  in  the  dark  was  much  higher  than  its  resistance  in  the  light  and  consequently  the  LED  glows  brighter  in  the  light  than  in  the  dark.

In  the  end,  the  mulMmeter  was  removed  and  the  LDR  and  resistor  were  connected  in  series.  It  was  observed  that  the  intensity  with  which  the  LED  glows  decreases  when  the  top  surface  of  LDR  was  covered  with  a  finger.  The  intensity  of  glow  increased  when  the  finger  is  removed.  Thus  the  LDR  acts  as  a  variable  resistor  whose  resistance  decreases  in  the  light  and  increases  in  the  dark.

Have  a  look  at  what  we  provide  in  our  Project  Kit!

CoolJunk   is   India's   fastest   growing  DIY   (do-­‐it-­‐yourself)   kits   company   focused   on   project-­‐based   learning   in  science,   engineering   and   technology.  Having   20,000   users   in   India,  US,   Singapore,   Middle   East   and   New  Zealand,  the  CoolJunk  kits  are  known   for  quality,  innovaMon   and  high  producMon  value.  CoolJunk  has  been  featured   in   naMonal   and   internaMonal   journals   including   Wallstreet,   Yourstory,   Hindu   Business   Line,  NextBigWhat  and  was  tagged  as  the  coolest  Indian  start-­‐up  in  IAN  Bootcamp-­‐2011.  

You  may  also  refer  to  the  video:  LDRFor  more  projects  visit  our  website:  CoolJunk  

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