Tuesday, March 8, 2011
Monday, March 7, 2011
Sunday, March 6, 2011
Saturday, March 5, 2011
Friday, March 4, 2011
Thursday, March 3, 2011
VAN DE GRAAFF
VAN DE GRAAFF GENERATOR:
PRINCIPLE:
*IT WORKS ON THE PRINCIPLE OF ELECTROSTATIC INDUCTION AND ACTION OF POINTS.CONSTRUCTION:
* 'A' BE THE HOLLOW METALLIC SPHERE MOUNTED ON INSULATING PILLARS.* 'B' AND 'C' BE THE TWO PULLEYS.'B' IS MOUNTED AT THE CENTRE OF THE SPHERE AND 'C' IS MOUNTED NEAR THE BOTTOM.
* PULLEY 'C' IS DRIVEN BY AN ELECTRIC MOTOR.
*A SILK BELT MOVES OVER THE PULLEYS.
*'D' AND 'E' BE THE TWO COMB SHAPED CONDUCTORS HAVING SHARP NEEDLES WHICH ARE MOUNTED NEAR THE PULLEYS.
*COMB 'D' IS GIVEN A POSITIVE POTENTIAL (10^4 V) BY A POWER SUPPLY.
*COMB 'E' IS CONNECTED TO THE INNER SIDE OF THE HOLLOW SPHERE.
WORKING:
*SINCE HIGH ELECTRIC FIELD IS AT 'D' AIR GETS IONISED DUE TO ACTION OF POINTS.
*NOW THE NEEDLE ATTRACTS NEGATIVE CHARGES AND REPELS POSITIVE CHARGES TOWARDS THE BELT.
*THE POSITIVE CHARGES STICK TO THE BELT, MOVES UP AND REACHES 'E'.
*'E' ACQUIRES NEGATIVE CHARGES DUE TO ELECTROSTATIC INDUCTION AND SPHERE ACQUIRES POSITIVE CHARGES WHICH ARE DISTRIBUTED ON ITS OUTER SURFACE.
*THE HIGH ELECTRIC FIELD AT 'E' IONISES THE AIR AND HENCE NEGATIVE CHARGES ARE REPELLED TOWARDS THE BELT.
*DUE TO THIS THE POSITIVE CHARGES ARE NEUTRALISED BEFORE THE BELT MOVES OVER THE PULLEY.
*SO THE DESCENDING BELT IS LEFT UNCHARGED.
*THE POTENTIAL OF THE SPHERE KEEPS ON INCREASING AND REACHES A MAXIMUM OR LIMITING VALUE.
*AFTER THIS STAGE LEAKEGE OF CHARGES OCCUR DUE TO IONISATION OF AIR.
ROBERT J.VAN DE GRAAFF |
USES:
*USED TO PRODUCE LARGE ELECTROSTATIC POTENTIAL DIFFERENCE UP TO 10^7 V.
*THIS HIGH VOLTAGE IS USED TO ACCELERATE THE POSITIVE IONS (PROTONS,DEUTRONS ) FOR NUCLEAR FISSION PROCESS.
Wednesday, March 2, 2011
VOLTAIC CELL
ALESSANDRO VOLTA |
*IT IS A SIMPLE CELL WHICH CONVERTS CHEMICAL ENERGY IN TO ELECTRICAL ENERGY.
*ANODE - COPPER
CATHODE - ZINC
ELECTROLYTE - Dil.H2SO4
EMF - 1.08 V
*IONISATION TAKES PLACE AT THE CATHODE.
*TWO ELECTRONS LEFT AT THE CATHODE AND Zn IONS PASS IN TO THE SOLUTION i.e.,
Zn + Dil.H2SO4 ------> ZnSO4 + 2H + 2 electrons
*TWO HYDROGEN IONS ARE DISCHARGED AT THE ANODE. CURRENT FLOWS CONTINUOUSLY IN THE EXTERNAL CIRCUIT AS LONG AS ELECTRONS ARE AVAILABLE AT THE CATHODE.
*WHEN THE ELECTRODES ARE CONNECTED BY A WIRE EXTERNALLY, CURRENT FLOW FROM COPPER TO ZINC OUTSIDE THE CELL AND CURRENT FLOWS FROM ZINC TO COPPER INSIDE THE CELL.
*DUE TO OPPOSITE CHARGES ON THE TWO ELECTRODES A POTENTIAL DIFFERENCE IS PRODUCED BETWEEN COPPER AND ZINC WHERE COPPER IS AT HIGHER POTENTIAL THAN ZINC.
Tuesday, March 1, 2011
LEAD ACID ACCUMULATORS
LEAD ACID ACCUMULATOR:
*IT IS ONE OF THE SECONDARY CELLS.
*ANODE - PbO2 ( LEAD OXIDE )
CATHODE - SPONGY LEAD (Pb)
ELECTROLYTE - Dil.H2SO4
EMF - 2.2 V
SPECIFIC GRAVITY OF THE ELECTROLYTE - 1.28
*THESE ARE PLACED IN A CONTAINER MADE UP OF HARD RUBBER OR GLASS OR CELLULOID.
*THE ELECTRODES ARE SEPARATED BY INSULATING MATERIALS AND ASSEMBLED TO GIVE LOW INTERNAL RESISTANCE SO THAT HIGH CURRENT IS DELIVERED.
WORKING
*AS THE CELL IS CONNECTED IN A CIRCUIT EXTERNALLY OXIDATION REACTION TAKES PLACE AT THE CATHODE.
*SPONGY LEAD REACTS WITH Dil.H2SO4 AND PRODUCES PbSO4 AND TWO ELECTRONS.
Pb (SPONGY) + Dil.H2SO4 -----> PbSO4 + 2 electrons
*ELECTRONS FLOW FROM CATHODE TO ANODE EXTERNALLY ( REDUCTION REACTION TAKES PLACE AT THE ANODE )
*PbO2 REACTS WITH Dil.H2SO4 AND PRODUCES PbSO4 i.e.,
PbO2 + Dil.H2SO4 ------> Pb(SO4)2 +2H2O
*TWO ELECTRONS AND Pb IONS ARE NEUTRALISED IN THIS PROCESS.
*NOW THE CURRENT FLOW FROM ANODE TO CATHODE.
*AS THE CELL IS DISCHARGED BY DRAWING CURRENT FROM IT, THE EMF FALLS TO ABOUT 2 VOLTS.
*DURING CHARGING PROCESS CHEMICAL REACTIONS ARE REVERSED.
*
GASTON PLANTE |
*ANODE - PbO2 ( LEAD OXIDE )
CATHODE - SPONGY LEAD (Pb)
ELECTROLYTE - Dil.H2SO4
EMF - 2.2 V
SPECIFIC GRAVITY OF THE ELECTROLYTE - 1.28
*THESE ARE PLACED IN A CONTAINER MADE UP OF HARD RUBBER OR GLASS OR CELLULOID.
*THE ELECTRODES ARE SEPARATED BY INSULATING MATERIALS AND ASSEMBLED TO GIVE LOW INTERNAL RESISTANCE SO THAT HIGH CURRENT IS DELIVERED.
WORKING
*AS THE CELL IS CONNECTED IN A CIRCUIT EXTERNALLY OXIDATION REACTION TAKES PLACE AT THE CATHODE.
*SPONGY LEAD REACTS WITH Dil.H2SO4 AND PRODUCES PbSO4 AND TWO ELECTRONS.
Pb (SPONGY) + Dil.H2SO4 -----> PbSO4 + 2 electrons
*ELECTRONS FLOW FROM CATHODE TO ANODE EXTERNALLY ( REDUCTION REACTION TAKES PLACE AT THE ANODE )
*PbO2 REACTS WITH Dil.H2SO4 AND PRODUCES PbSO4 i.e.,
PbO2 + Dil.H2SO4 ------> Pb(SO4)2 +2H2O
*TWO ELECTRONS AND Pb IONS ARE NEUTRALISED IN THIS PROCESS.
*NOW THE CURRENT FLOW FROM ANODE TO CATHODE.
*AS THE CELL IS DISCHARGED BY DRAWING CURRENT FROM IT, THE EMF FALLS TO ABOUT 2 VOLTS.
*DURING CHARGING PROCESS CHEMICAL REACTIONS ARE REVERSED.
*
LECLANCHE CELL
LECLANCHE CELL:
* IT IS A PRIMARY CELL
* IT IS USED FOR SUPPLYING INTERMITTENT CURRENT
* ANODE - CARBON ELECTRODE ( PACKED IN A POROUS POT CONTAINING MnO2 + CHARCOAL POWDER )
CATHODE - ZINC ROD
ELECTROLYTE -NH4Cl ( IN WHICH ANODE & CATHODE ARE IMMERSED )
EMF - 1.5 V
CURRENT - 0.25 A
*DUE TO OXIDATION REACTION ZINC REACTS WITH AMMONIUM CHLORIDE GIVING OUT Zn IONS AND 2 ELECTRONS i.e.,
*Zn + 2NH4Cl -----> 2 NH3 (GAS) + ZnCl2 + 2 H + 2 electrons
( OXIDATION REACTION TAKES PLACE AT THE CATHODE )
*AMMONIA GAS ESCAPES AND H2 IONS DIFFUSE THROUGH THE PORES OF POROUS POT AND REACT WITH MnO2.
*2 HYDROGEN IONS DISCHARGED AT THE ANODE.
*WHEN THE CELL IS CONNECTED BY A WIRE EXTERNALLY TWO ELECTRONS ON THE Zn ROD PASS THROUGH THE EXTERNAL CIRCUIT AND REACH THE CARBON ROD NEUTRALISING THE POSITIVE CHARGE.
*THUS CURRENT FLOW FROM CARBON TO ZINC.
* IT IS A PRIMARY CELL
* IT IS USED FOR SUPPLYING INTERMITTENT CURRENT
* ANODE - CARBON ELECTRODE ( PACKED IN A POROUS POT CONTAINING MnO2 + CHARCOAL POWDER )
CATHODE - ZINC ROD
ELECTROLYTE -NH4Cl ( IN WHICH ANODE & CATHODE ARE IMMERSED )
EMF - 1.5 V
GEORGES LECLANCHE |
*DUE TO OXIDATION REACTION ZINC REACTS WITH AMMONIUM CHLORIDE GIVING OUT Zn IONS AND 2 ELECTRONS i.e.,
*Zn + 2NH4Cl -----> 2 NH3 (GAS) + ZnCl2 + 2 H + 2 electrons
( OXIDATION REACTION TAKES PLACE AT THE CATHODE )
*AMMONIA GAS ESCAPES AND H2 IONS DIFFUSE THROUGH THE PORES OF POROUS POT AND REACT WITH MnO2.
*2 HYDROGEN IONS DISCHARGED AT THE ANODE.
*WHEN THE CELL IS CONNECTED BY A WIRE EXTERNALLY TWO ELECTRONS ON THE Zn ROD PASS THROUGH THE EXTERNAL CIRCUIT AND REACH THE CARBON ROD NEUTRALISING THE POSITIVE CHARGE.
*THUS CURRENT FLOW FROM CARBON TO ZINC.
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