3.5(2) DC Theory Flashcards
Chemical energy converted to electrical energy is known as?
electrochemical action
What will vary the voltage across the electrodes of a cell?
The material the electrodes are made of and the composition of the electrolyte.
What factors effect the internal resistance of a cell?
size of the electrodes and the distance between them.
How can you lower internal resistance of a cell?
by making the electrodes larger or bringing them closer together.
How are secondary cells able to be recharged?
chemical action which produces the electric current can be reversed returning the cell to the charged condition.
What happens to the electrodes in a primary cell?
Chemical action eats away one of the electrodes usually the negative electrode., causing it to be replaced.
What are the 4 basic types of wet cells?
Lead acid, mickel cadmium, silver zinc, silver cadmium
In a secondary cell the electrodes and electrolyte are altered when
the cell delivers current, these cells may be restored to original condition by forcing current through them in the opposite direction of discharge.
What type of materials are used in alead acid battery?
Positive plates = lead peroxide, negative plates = pure spongy lead, electrolyte = sulfuric acid and water.
What is the V of a open circuit (no load) lead acid CELL
2V
In a battery there is always one more plate of which polarity?
There is always one more negative plate then positive plate.
What is the purpose of the seperators between the plates of a bettery?
Hold the plates apart while allowing free movement of the ELECTROLYTE!
How are the plates connected internally of the battery?
In series by link connectors, one end of the positive plates will act as the terminal, one end of the negative plates will act as the other negative terminal.
In a lead acid battery if a cell fails what must be done?
The battery must be replaced.
What is the specific gravity of a fully charged lead acid battery?
1.270 twelve seventy
When will electron flow stop and the battery be discharged?
When both plates are converted to lead sulfate no further chemical action is possible.
During battery discharge what happens to the negatively charged sulfate ions?
Negatively charged sulfat ions combine with the lead in the plates and form LEAD SULFATE., giving up their charge creating an EXCESS of electrons on the negative plate.
During discharge what happens to the hydrogen ions?
Hydrogen ions go to the positive plate and combine with oxygen of the LEAD PEROXIDE forming water, stealing electrons from the positive plate forming LEAD SULFATE on positive plate.
When the discharging battery is connected to a load what happens to the electrons?
Positive plate ends up with a defficiency of electrons, while the negative plate has an excess. forcing the electrons around the circuit from negative to positive.
How is a battery charged?
Current flow is reversed, sulfate ions are driven back into the solution off the electrodes, the plates return to original composition of spongy lead (-) and lead peroxcide (+).
What materials are used in the Nicad Battery?
Positive = Nickel hydroxide, Negative = cadmium hydroxide, Electrolyte = Potassium hydroxide (Discharged state)
What is an advantage of the nickel cadmium battery?
It can stand in the discharged state with little to none detioration.
What is the SG of a Nicad battery?
About 1.300
What are some advantages o the nicad battery?q
Charged in shorter time, stay ide longer in any state of charge, be charged and discharged any number of times.
What is the open circuit (no-load) cell voltage for a nicad?
1.3V
How is thermal runaway indicated?
Battery charging current rises instead of falling as the charge progresses., high temperature lowers internal resistance causing excessive current draw.
What are the materials of a silver zinc cell?
Positive = Silver oxide, Negative terminal = zinc, electrolyte = potassium hydroxide.
Advantages of a silver zinc cell?
High out put, ideal for miniture devices.
Cells connected in series =?
Higher Voltage
Cells connected in parallel?
Higher current
What is a disadvantage to batteries connected in series?
The internal resistance of the batteries add up lowering the current supply capability for the circuit.
Explain batteries connected in parallel.
Voltage will stay the same but total current output increases. if one cell shorts the entire system fails as all cells will discharge through the shorted circuit.
How is the Potential difference (Voltage) measured on a thermocouple?
Measured at the cold junction between the 2 dissimilar metals.
Generating potential difference via heat is named.
Seebeck effect. (10mV)
Thermo couple type T?
Copper Constantan upto 400c
Thermocouple type J?
Iron constantan - range upto 850C
Thermo couple type K
Chromel alumel - range upto 1200C
What type of material are photovoltaic cells made up?
Semiconducting materials, N type and P type silicon
