Electric Cells | Physics for JAMB PDF Download

Simple Voltaic Cell and Its Defects

• A simple voltaic cell consists of two different metal electrodes (anode and cathode) immersed in an electrolyte solution.
• The anode is the negative electrode where oxidation occurs, and the cathode is the positive electrode where reduction occurs.
• The electrolyte serves as a medium for the flow of ions between the electrodes.
• When the electrodes are connected by a wire, electrons flow from the anode to the cathode, creating an electric current.

Defects of the Simple Voltaic Cell and Their Corrections

1. Internal Resistance:

• The electrolyte and the electrodes have resistance, causing a drop in voltage within the cell.
• To minimize this, electrodes with larger surface area can be used, and a more concentrated electrolyte can be employed.

2.. Polarization:

• As the cell operates, a build-up of reaction products may occur, hindering further redox reactions.
• To overcome polarization, a porous barrier or salt bridge can be added to allow ion flow and maintain charge neutrality.

Daniel Cell, Leclanché Cell (Wet and Dry)

1. Daniel Cell:

• The Daniel cell consists of a zinc anode, a copper cathode, and a sulfuric acid electrolyte.
• The zinc electrode undergoes oxidation, producing Zn2+ ions, while copper ions from the electrolyte are reduced at the cathode.
• This cell provides a stable voltage and is commonly used as a reference cell.

2. Leclanché Cell (Wet):

• The Leclanché wet cell consists of a zinc anode, a carbon cathode surrounded by manganese dioxide (MnO₂), and an ammonium chloride electrolyte.
• The zinc electrode undergoes oxidation, producing Zn²⁺ ions, while the reduction of MnO₂ occurs at the cathode.
• This cell is commonly used in flashlights and other low-power devices.

3. Leclanché Cell (Dry):

• The Leclanché dry cell is a variation of the wet cell, where the ammonium chloride electrolyte is replaced with a paste.
• The rest of the components remain the same.
• This cell is commonly used in portable electronic devices like radios and toys.

Lead-Acid Accumulator and Nickel-Iron (NiFe) Accumulator

1. Lead-Acid Accumulator:

• The lead-acid accumulator consists of lead and lead dioxide electrodes immersed in a sulfuric acid electrolyte.
• During discharge, lead undergoes oxidation at the anode, while lead dioxide is reduced at the cathode.
• This cell is used in automobile batteries and offers high current capability.

2. Nickel-Iron (NiFe) Accumulator:

• The nickel-iron accumulator, also known as the Edison battery, consists of nickel and iron electrodes immersed in an alkaline electrolyte of potassium hydroxide.
• Nickel undergoes oxidation at the anode, while iron is reduced at the cathode during discharge.
• This cell has a long life span, high durability, and is often used in renewable energy systems.

Advantages of Lead-Acid and Nickel-Iron Accumulators

1. Lead-Acid:

• Relatively low cost compared to other rechargeable batteries.
• Can deliver high currents.
• Suitable for starting engines and short-duration applications.

2. Nickel-Iron:

• Long life span, lasting up to 20 years.
• High durability, tolerant to deep discharges.
• Environmentally friendly due to the use of non-toxic materials.

Maintenance of Cells and Batteries

• Regular inspection and cleaning of terminals to prevent corrosion.
• Replenishing or replacing electrolyte solutions as needed.
• Avoiding overcharging or deep discharging, which can damage the battery.
• Proper storage conditions to prevent self-discharge.
• Monitoring battery temperature to prevent overheating.
• Replacing damaged or worn-out components.

Arrangement of Cells

• Series Combination:
  • Cells are connected in a series by connecting the positive terminal of one cell to the negative terminal of the next.
  • The total voltage is the sum of individual cell voltages.
  • The current remains the same in each cell.
• Parallel Combination:
  • Cells are connected in parallel by connecting all positive terminals together and all negative terminals together.
  • The voltage remains the same in each cell.
  • The total current is the sum of individual cell currents.

Efficiency of a Cell

• The efficiency of a cell is the ratio of useful electrical energy output to the chemical energy input during the cell's operation.
• It is expressed as a percentage.
• Efficiency = (Useful output energy / Input energy) x 100%
• Factors Affecting Efficiency:
  • Internal resistance: Higher resistance results in energy loss.
  • Polarization: Increased polarization decreases efficiency.
  • Temperature: Higher temperatures can improve or reduce efficiency, depending on the cell type.
  • Type of cell: Different types of cells have varying inherent efficiencies.