3.5 DC Sources Of Electricity Flashcards
In a primary cell is the electrochemical processes taking place reversible?
No
Can primary cells immediately supply voltage without charging beforehand?
Yes
Can primary cells be recharged or reused?
No but they can be recycled
What is capacity of a battery?
The quantity of electricity
1 ampere-hour is how many coulombs?
3,600 coulombs
What determines a batteries capacity?
Their construction and size
Most primary cells are wet or dry cells?
Dry cells
Why should zinc-carbon batteries not be used in devices for extended periods of time?
The zinc container oxidises causing the contents to leak
Is the electrochemical reaction in a secondary cell reversible?
Yes
How can the chemical reactants be restored in a secondary cell?
By running a charging current through them
In aircraft storage what are the secondary cell made from?
Lead acid or nickel cadmium
How are the aircraft storage batteries connected?
In series within the battery case
A group of cells connected together in series is called?
A battery of cells (abbreviated to ‘battery’)
Lead acid cells have a charged voltage of?
2.2volts
Lead acid cells have a final discharge voltage of?
1.83volts
A lead acid cell consists of?
-positive lead peroxide plates
-negative pure sponges lead plates
-a liquid electrolyte (30%acid 70% water)
When is a lead acid cell said to be discharged?
When the plates go through a chemical process and are coated in lead sulphate where no further chemical action takes place
Nickel cadmium cells have a voltage of?
1.2 volts
When a nickel cadmium cell is discharged what will the voltage fall to?
1.0 volts
What are the components of a nickel cadmium cell?
-positive nickel oxyhydroxides plates
-negative metallic cadmium plates
-potassium hydroxide electrolyte
When is the only time you should refill a nickel cadmium battery?
When its fully charged
When is the electrolyte level in a nickel cadmium battery at its lowest?
After discharge
How do you create a series of connections for batteries?
By connecting unlike terminals
The series connection of power sources increases the?
Voltage
What stays the same through a series circuit?
The current
What happens to the internal resistance of the battery if its cells are connected in series?
It increases
Why is it better to connect like owner sources. In parallel than in series?
It provides the same voltage but lowers the total internal resistance
Why should you only connect like power sources in parallel instead of different power sources?
Because connecting different power sources can create an unintended circulating current
A power source (battery) generates voltage, what is this also known as?
Source voltage
Why is the total source voltage not available at the terminals?
Due to the internal resistance
What is terminal voltage?
The amount of voltage you have at the terminals due to internal resistance
What is the definition of a short circuit?
The terminals of the battery are directly connected to each other
What is a short-circuit current?
When a battery has been short circuited and a high current flows in the circuit
What is the short circuit current limited by?
The international resistance of the battery
The total source voltage drops at the?
Internal resistance
What happens if the short circuit currents are too high?
It will destroy the power source
What increases as the battery discharges?
The internal resistance
What is a thermocouple?
When two different metals are connected and heated to created a voltage
What is the voltage from a thermocouple referred to as?
Thermoelectric voltage
In aviation where are thermocouples mainly used?
To measure exhaust gas temperatures of engines
In aviation what are the two main alloys used in a thermocouple?
Chrome and alumel
How does a phot-cell work?
When exposed to light it releases electrons to generate a voltage (like a light sensor)
What are photocells used for on an aircraft?
Automatic light level adjustment for the crew
