3.5 DC Sources Of Electricity Flashcards
What is the nominal initial voltage of a zinc carbon battery?
1.5v
Why is a dry cell called “dry”
Because it’s electrolyte is a paste
What is the electrolyte in zinc carbon cells made of?
A paste mainly made of magnesium oxide.
What is the charged and discharged voltage of a lead acid battery?
2.2v and 1.83v when discharged
What is the electrolyte made of in a lead acid battery?
sulphuric acid (30%) and distilled water (70%)
What is the charged vs discharged voltage of a nickel cadmium cell
1.2v and 1.0v
What is the electrolyte in a nickel cadmium cell?
Potassium hydroxide. The level will rise during charging, so must be refilled when fully charged
Advantages of nickel cadmium compared to lead acid cells
- Tolerates higher discharge currents
- Closed circuit voltage remains almost constant throughout discharge
- Higher energy density
- Greater number of charge/discharge cycles
Disadvantages of nickel cadmium compared to lead acid.
- More costly
- More complicated charging requirements
- Risk of thermal runaway. As the battery temp. rises, the internal resistance decreases
- High toxicity of cadmium
Silver oxide coin cells.
Voltage: ?
Properties: ?
Have high energy density.
Contain potassium hydroxide, zinc, silver oxide
Low voltage depression.
Rated voltage of 1.55v
Used in watches, calculators, hearing aids
Lithium coin cells
High rated voltages of up to 3.5v.
High energy density.
High lifespan.
Used in pacemakers, cameras, etc
Mercury oxide coin cells
Zinc powder as negative pole.
Mercury oxide as positive pole.
Electrolyte is potassium hydroxide
CONSTANT Voltage of 1.3v even in use
Total voltage and resistance when cells are in series
Vt = V1 + V2 + V3
Rt = R1 + R2 + R3
What happens to voltage and resistance when cells are connected in parallel
The total resistance decreases.
Total voltage is the same as the voltage of one cell.
Can therefore provide a larger supply of current
