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Questions and Answers
What is the primary function of the simplest cell, known as a galvanic or voltaic cell?
What is the primary function of the simplest cell, known as a galvanic or voltaic cell?
What materials make up the electrodes in a dry cell?
What materials make up the electrodes in a dry cell?
Which of the following describes the role of the electrolyte in a galvanic cell?
Which of the following describes the role of the electrolyte in a galvanic cell?
What characteristic must the container of a voltaic cell have?
What characteristic must the container of a voltaic cell have?
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What triggers the flow of electrons when a load is connected to a cell?
What triggers the flow of electrons when a load is connected to a cell?
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In a dry cell, what form does the electrolyte take?
In a dry cell, what form does the electrolyte take?
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What is the primary chemical component in the electrolyte of a galvanic cell?
What is the primary chemical component in the electrolyte of a galvanic cell?
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What is the historical significance of Alessandro Volta in the context of electricity?
What is the historical significance of Alessandro Volta in the context of electricity?
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Which component of a lead-acid battery is typically colored red and marked with a (+)?
Which component of a lead-acid battery is typically colored red and marked with a (+)?
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What is a primary cell?
What is a primary cell?
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What is the specific gravity of a fully charged lead-acid battery electrolyte at 20°C?
What is the specific gravity of a fully charged lead-acid battery electrolyte at 20°C?
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What effect does the process of charging have on sulfate ions (SO4) in a lead-acid battery?
What effect does the process of charging have on sulfate ions (SO4) in a lead-acid battery?
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How does internal resistance affect the current a cell can supply?
How does internal resistance affect the current a cell can supply?
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What is a key feature that differentiates alkaline cells from carbon-zinc cells?
What is a key feature that differentiates alkaline cells from carbon-zinc cells?
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Which ion is associated with a deficiency of electrons in a lead-acid battery during discharge?
Which ion is associated with a deficiency of electrons in a lead-acid battery during discharge?
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What happens to a primary cell when its negative electrode deteriorates?
What happens to a primary cell when its negative electrode deteriorates?
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What is the primary component of the electrolyte in a fully charged lead-acid battery?
What is the primary component of the electrolyte in a fully charged lead-acid battery?
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What chemical reaction occurs during the discharging process of a lead-acid battery?
What chemical reaction occurs during the discharging process of a lead-acid battery?
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What is typically used as the electrolyte in a lead-acid battery?
What is typically used as the electrolyte in a lead-acid battery?
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What is the result of the lead-acid battery reaching a fully discharged state?
What is the result of the lead-acid battery reaching a fully discharged state?
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Which materials make up the positive and negative plates of a lead-acid battery?
Which materials make up the positive and negative plates of a lead-acid battery?
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What contributes to increased internal resistance in electric cells?
What contributes to increased internal resistance in electric cells?
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Which statement is true about secondary cells?
Which statement is true about secondary cells?
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What is a disadvantage of dry cells?
What is a disadvantage of dry cells?
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Which of the following accurately identifies the major materials of a nickel-cadmium (NICAD) cell?
Which of the following accurately identifies the major materials of a nickel-cadmium (NICAD) cell?
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What is the effect of both overcharging and undercharging on a lead-acid battery?
What is the effect of both overcharging and undercharging on a lead-acid battery?
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Why are separators used in lead-acid batteries?
Why are separators used in lead-acid batteries?
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What characterizes alkaline cells compared to carbon-zinc cells?
What characterizes alkaline cells compared to carbon-zinc cells?
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What is the specific gravity of sulfuric acid, indicating its density compared to water?
What is the specific gravity of sulfuric acid, indicating its density compared to water?
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Which statement describes the flow of electrons in a lead-acid battery when connected to an external circuit?
Which statement describes the flow of electrons in a lead-acid battery when connected to an external circuit?
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What is the approximate nominal voltage of a lead-acid cell?
What is the approximate nominal voltage of a lead-acid cell?
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What is the primary difference between a lead-acid cell and a nickel-cadmium cell?
What is the primary difference between a lead-acid cell and a nickel-cadmium cell?
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What component of the lead-acid battery contains the individual cells?
What component of the lead-acid battery contains the individual cells?
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What is the role of the vent plugs in a lead-acid battery?
What is the role of the vent plugs in a lead-acid battery?
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Which statement is true regarding the arrangement of plates in a lead-acid battery?
Which statement is true regarding the arrangement of plates in a lead-acid battery?
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What is the total current supplied by four cells connected in parallel, each allowing 1/8 ampere?
What is the total current supplied by four cells connected in parallel, each allowing 1/8 ampere?
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How are the three 1.5-volt cells connected to achieve a voltage of 4.5 volts?
How are the three 1.5-volt cells connected to achieve a voltage of 4.5 volts?
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What is the purpose of the cold junction in thermocouples?
What is the purpose of the cold junction in thermocouples?
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Which thermocouple combination is typical for gas turbine engines?
Which thermocouple combination is typical for gas turbine engines?
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What range of frequency corresponds to visible light?
What range of frequency corresponds to visible light?
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What happens when a photon hits silicon and is absorbed?
What happens when a photon hits silicon and is absorbed?
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What is the principle behind the Seebeck effect?
What is the principle behind the Seebeck effect?
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What does the term 'EMF' stand for in the context of thermocouples?
What does the term 'EMF' stand for in the context of thermocouples?
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What is the main function of a solar cell?
What is the main function of a solar cell?
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What does each cell connected in a series contribute to the total voltage?
What does each cell connected in a series contribute to the total voltage?
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What happens if two dissimilar metals are joined without care in a thermocouple?
What happens if two dissimilar metals are joined without care in a thermocouple?
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How is light measured when discussing its properties?
How is light measured when discussing its properties?
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Which type of current do solar panels produce?
Which type of current do solar panels produce?
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What happens to an electron when it absorbs a photon in a semiconductor?
What happens to an electron when it absorbs a photon in a semiconductor?
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What creates the electric field in a solar cell?
What creates the electric field in a solar cell?
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How do electron-hole pairs contribute to the operation of a solar cell?
How do electron-hole pairs contribute to the operation of a solar cell?
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What role does the antireflective coating play in a solar cell?
What role does the antireflective coating play in a solar cell?
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Why is the electron flow in a solar cell considered directional?
Why is the electron flow in a solar cell considered directional?
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What is the maximum theoretical efficiency of a simple photovoltaic cell?
What is the maximum theoretical efficiency of a simple photovoltaic cell?
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What happens to electrical neutrality when electrons and holes recombine?
What happens to electrical neutrality when electrons and holes recombine?
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Which statement best describes the movement of holes in the semiconductor lattice?
Which statement best describes the movement of holes in the semiconductor lattice?
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What property of silicon necessitates the use of a glass cover on solar cells?
What property of silicon necessitates the use of a glass cover on solar cells?
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In which direction do electrons flow when a current path is provided in a solar cell?
In which direction do electrons flow when a current path is provided in a solar cell?
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What is the primary advantage of nickel-cadmium cells over lead-acid batteries?
What is the primary advantage of nickel-cadmium cells over lead-acid batteries?
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Which electrodes are used in a nickel-cadmium cell?
Which electrodes are used in a nickel-cadmium cell?
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What is the typical open-circuit voltage of a nickel-cadmium cell?
What is the typical open-circuit voltage of a nickel-cadmium cell?
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What causes thermal runaway in nickel-cadmium batteries?
What causes thermal runaway in nickel-cadmium batteries?
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Which of the following best describes a secondary cell?
Which of the following best describes a secondary cell?
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What is a safety precaution to take during thermal runaway of a nickel-cadmium battery?
What is a safety precaution to take during thermal runaway of a nickel-cadmium battery?
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What happens to the negative electrode of a nickel-cadmium cell when discharged?
What happens to the negative electrode of a nickel-cadmium cell when discharged?
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Which electrolyte is used in nickel-cadmium batteries?
Which electrolyte is used in nickel-cadmium batteries?
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Which characteristic of nickel-cadmium batteries makes them popular for military applications?
Which characteristic of nickel-cadmium batteries makes them popular for military applications?
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What is a method to neutralize spilled potassium hydroxide on aircraft?
What is a method to neutralize spilled potassium hydroxide on aircraft?
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What can indicate a thermal runaway condition in a nickel-cadmium battery?
What can indicate a thermal runaway condition in a nickel-cadmium battery?
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Which of the following is a consequence of thermal runaway?
Which of the following is a consequence of thermal runaway?
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What occurs to the separator material in a nickel-cadmium battery during thermal runaway?
What occurs to the separator material in a nickel-cadmium battery during thermal runaway?
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What is a key feature of the silver-zinc cell?
What is a key feature of the silver-zinc cell?
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What is a characteristic of silver-zinc cells compared to lead-acid or nickel-cadmium cells?
What is a characteristic of silver-zinc cells compared to lead-acid or nickel-cadmium cells?
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Which electrolyte is used in both silver-zinc and nickel-cadmium cells?
Which electrolyte is used in both silver-zinc and nickel-cadmium cells?
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What does connecting cells in series achieve?
What does connecting cells in series achieve?
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How does connecting cells in parallel affect voltage?
How does connecting cells in parallel affect voltage?
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What potential issue arises if one cell in a series connection opens?
What potential issue arises if one cell in a series connection opens?
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What practical applications are ideal for silver oxide cells?
What practical applications are ideal for silver oxide cells?
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Which configuration allows for increased current capacity without changing voltage?
Which configuration allows for increased current capacity without changing voltage?
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What is the effect of internal resistance when cells are connected in series?
What is the effect of internal resistance when cells are connected in series?
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What consequence results from short-circuiting a cell in a parallel configuration?
What consequence results from short-circuiting a cell in a parallel configuration?
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What precaution must be taken when connecting cells in series?
What precaution must be taken when connecting cells in series?
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What role does the surface area of electrodes play in a cell's performance?
What role does the surface area of electrodes play in a cell's performance?
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Why might silver-zinc cells be limited to specialized applications?
Why might silver-zinc cells be limited to specialized applications?
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What is the nominal voltage rating for aircraft batteries typically?
What is the nominal voltage rating for aircraft batteries typically?
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How are the cells of a battery physically arranged?
How are the cells of a battery physically arranged?
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Study Notes
Cells - Introduction
- A cell is a device that converts chemical energy into electrical energy.
- The basic cell is called either a galvanic or voltaic cell and consists of two electrodes in an electrolyte solution.
Components of a Cell
- Container: Holds the electrolyte and can act as one of the electrodes.
- Electrodes: Conduct electricity into and out of the electrolyte. They are the negative and positive terminals.
- Electrolyte: A solution that interacts with the electrodes to create a path for electron flow. This can be an acid, salt, or alkaline solution.
Electrochemical Action
- All batteries operate on an electrochemical reaction.
- Alessandro Volta's first battery in 1800 used layers of zinc, salt water soaked blotting paper, and silver. This is the basis for modern batteries.
- Voltage depends on the materials of the electrodes and the electrolyte.
- Current depends on the resistance of the circuit, including the cell's internal resistance.
- Larger electrodes and shorter distances between them (without touching) lead to lower internal resistance and higher current.
Primary Cells
- Primary cells cannot be recharged. One electrode degrades as the cell produces current.
- The dry cell is the most popular type of primary cell. It's not truly dry, but has a moist paste electrolyte.
- Alkaline cells are similar to carbon-zinc cells but use potassium hydroxide in the electrolyte for better performance.
Secondary Cells
- Secondary cells can be recharged by reversing the chemical reaction.
- Common types include:
- Lead-acid: Used in car batteries
- Nickel-cadmium (NiCad): Used in high-performance applications
- Silver-zinc: High-power applications requiring a short lifespan
- Silver-cadmium: Smaller applications demanding high performance
Lead-Acid Battery
- Lead-acid batteries consist of:
- Positive plates of lead peroxide (PbO2)
- Negative plates of pure lead (Pb)
- Sulfuric acid (H2SO4) and water (H2O) electrolyte
- Nominal voltage of a lead-acid cell is approximately 2 volts.
- Discharging: Sulfuric acid breaks down into ions, sulfate ions react with lead to form lead sulfate, and hydrogen ions react with oxygen to form water.
- Charging: Current flows in reverse. Sulfate ions are driven back into solution with hydrogen ions to reform sulfuric acid.
- Specific Gravity: The density of the electrolyte reflects the state of charge. A higher specific gravity equates to a fuller charge.
Nickel-Cadmium (NiCad) Cell
- Advantages over lead-acid:
- Less maintenance
- Can stand discharged for long periods without damage
- Nickel-cadmium cells use:
- Nickel hydroxide as the positive terminal
- Cadmium hydroxide as the negative terminal
- Potassium hydroxide and water as the electrolyte
-
Thermal Runaway:
- An uncontrolled rise in battery temperature caused by:
- High discharge/charging rates
- Damaged separators
- Decreasing internal resistance with increasing temperature
- Can lead to:
- Violent gassing due to boiling electrolyte
- Possible explosion
- An uncontrolled rise in battery temperature caused by:
Safety Precautions for Thermal Runaway
- Isolate electrical power (switch charger off).
- Do NOT disconnect battery terminals.
- Do NOT handle or move the battery for at least 30 minutes, and allow it to cool down for an extended period before attempting to remove vent caps.
- Examine the battery for signs of damage and recondition if necessary.
Neutralising Spills
- Lead-acid spills can be neutralized with a bicarbonate of soda solution (100 grams per 1 liter of water).
- Potassium hydroxide spills can be neutralized with a chromic acid solution on aircraft or a 3% boric acid or acetic acid (vinegar) solution off aircraft.
- Always flush spilled electrolyte from skin with copious amounts of cold water and seek medical attention.
Types of Secondary Cells
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Silver-zinc cells are used to power emergency equipment. They are lightweight and offer good electrical capacity, but they are expensive and have a limited life cycle.
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Silver-zinc cells use potassium hydroxide and water as electrolyte and feature a silver oxide positive terminal and a zinc negative terminal
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Nickel-zinc, nickel-cadmium, silver-cadmium, organic and inorganic lithium, and mercury cells are other types of secondary cells.
Combining Cells
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Connecting cells in series increases the voltage.
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Connecting cells in parallel increases the current capacity.
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A series-parallel network combines the benefits of both series and parallel connections, providing both increased voltage and current.
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Combining cells creates a battery, which is a group of cells that form a single power source.
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The total emf of a series connection of cells is the sum of their individual voltages.
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The current supply capability of a series connected battery is limited to that of a single cell because their internal resistances add up.
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Parallel connections share the current demand equally, preventing excessive voltage drops and decreasing internal resistance.
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In a parallel connection, the voltage remains the same, but the current capacity is increased.
Thermocouples
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Thermocouples are temperature sensors used in aircraft.
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They are used to sense engine cylinder head temperatures, turbine exhaust gas temperatures, and detect fires based on rapid temperature changes.
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Thermocouples generate an EMF through the Seebeck effect, which occurs when a junction of two dissimilar metals is heated.
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The EMF generated is proportional to the temperature difference between the hot junction and the cold junction.
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The cold junction is typically formed by the measurement meter.
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Aircraft use various thermocouple combinations, including copper-constantan (up to 400ºC), iron-constantan (up to 850ºC), and chromel-alumel (up to 1200ºC).
Light
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Light is a form of electromagnetic radiation visible to the human eye.
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It travels at 186,000 miles per second (300,000,000 meters per second) in a vacuum and has a frequency range from 300 to 300,000,000 gigahertz.
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Light is classified by wavelength:
- Below 400,000 gigahertz: Infrared light
- 400,000 to 750,000 gigahertz: Visible light
- Above 750,000 gigahertz: Ultraviolet light
Photoelectric Cells (Solar Cells)
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Solar cells convert sunlight directly into DC electricity.
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They are made of silicon doped with impurities that make them sensitive to light.
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Photons in sunlight strike the solar panel and are absorbed by semiconducting materials.
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This absorption releases electrons, creating a flow of electric current.
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Three possible outcomes when photons interact with silicon:
- Transmission: Photon passes through the silicon
- Reflection: Photon bounces off the silicon surface
- Absorption: Photon is absorbed, creating an electron-hole pair
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The electric field in a solar cell is created by the junction of N-type and P-type silicon.
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This field acts as a diode, allowing electrons to flow from the P-side to the N-side.
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When light hits the solar cell, electron-hole pairs are generated.
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The electric field pushes electrons to the N-side and holes to the P-side, creating a current flow.
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An antireflective coating is applied to solar cells to minimize reflection losses.
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Solar modules are created by connecting multiple cells in series and parallel to achieve desired voltage and current outputs.
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Solar cells can absorb up to 25% of sunlight energy, but typically absorb 15% or less.
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Description
This quiz explores the fundamental concepts of cells, including their components and the electrochemical processes they involve. Dive into the world of galvanic and voltaic cells, and understand how they generate electrical energy from chemical reactions. Perfect for students looking to solidify their knowledge in electrochemistry.
