Part of Made in India,Design Innovation

Workshop,2015

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PHYSICS INVESTIGATORY PROJECT ON

CHARGING AND DISCHARGING A CAPACITOR

Do  you  know  that  a  capacitor  is  so  ubiquitous  that  it  is  rare  that  an  electrical  or  electronic  product  does  not  include  at  least  one  for  some  purpose?  Besides  being  used  as  an  energy  storage  device,  it  is  used  in  filter  circuits,  tuning  circuits  (for  radio,  TV,  transmiMers  etc.)  and  also  as  shock  absorbers  in  voltage  stabilizers.  You  can  learn  about  the  funcRoning  of  a  capacitor  and  how  the  voltage  across  it  changes  when  it  gets  charged.

This  project  is  divided  into  two  phases.  In  the  first  phase,  a  resistor,  a  capacitor  and  an  LED  are  connected  in  series  on  the  breadboard.  The  mulRmeter  probes  are  connected  to  the  capacitor  for  a  constant  voltage  measurement  across  its  terminals,  before  supply  is  given  to  the  circuit.  Immediately  aTer  the  supply  is  given,  the  LED  starts  

to  glow  with  maximum  intensity  and  the  meter  shows  an  instantaneous  voltage  reading  of  0  V.  The  meter  will  show  a  conRnuously  increasing  voltage  which  becomes  steady  aTer  someRme.  The  LED  slowly  fades  out.  

The  iniRal,  transient  and  steady  voltages  were  observed  and  the  same  were  compared  with  theoreRcal  values  of  voltages  using  the  Rme  constant  (t  =RC)  calculaRons.  It  was  noted  that  the  voltage  across  the  capacitor  at  any  given  Rme  is  equal  to  the  sum  of  iniRal  voltage  and  63%  of  the  difference  between  the  baMery  voltage  and  the  iniRal  voltage  on  the  capacitor.  When  the  voltage-­‐Rme  graph  of  a  charging  capacitor  was  ploMed,  it  showed  that  the  voltage  in  the  capacitor  increases  exponenRally  and  then  becomes  constant.

In  the  second  phase,  the  baMery  was  removed  and  the  same  charged  capacitor  was  connected  in  parallel  to  the  series  combinaRon  of  another  LED  and  a  resistor.  It  was  found  that  the  LED  glows  for  a  moment  with  a  maximum  voltage  across  the  capacitor.  Similarly  as  above,  the  voltages  on  the  capacitor  in  different  states  were  compared  with  the  theoreRcal  voltages  calculated  using  the  Rme  

constant.  Note  that  in  this  case,  the  Rme  constant  is  the  Rme  the  capacitor  takes  to  discharge  37%  of  voltage  on  its  plates.  When  the  voltage-­‐Rme  graph  of  the  discharging  capacitor  was  ploMed,  it  showed  that  the  capacitor  loses  its  voltage  exponenRally  and  the  voltage  becomes  constant  aTer  some  Rme.

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,  innovaRon   and  high  producRon  value.  CoolJunk  has  been  featured   in   naRonal   and   internaRonal   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:  Charging  &  Discharging  a  Capacitor  CreaAng  spark  using  a  Capacitor

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