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Maharashtra State BoardSSC (English Medium) 8th Standard
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Syllabus

Electric cell

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Topics

  • Introduction
  • Definition: Electric Cell
  • Mechanism of Cell
  • Types of Electric Cells
  • Experiment
Maharashtra State Board: Class 8

Introduction of Electric Cell:

An electric cell is a device that provides energy to create a steady and uniform flow of electric charges through a circuit. It acts as a power source, ensuring that a constant potential difference (voltage) is maintained between its two terminals. This potential difference is necessary to push the electric charges, or current, through the circuit, powering devices connected to it.

Applications:

  1. Electric cells are versatile and used in a wide range of applications. They power small devices like wristwatches as well as larger systems like submarines.
  2. Different types of electric cells are designed to meet various energy needs. For example, solar cells are a type of electric cell that converts sunlight directly into electricity, making them environmentally friendly and useful for renewable energy solutions.
  3. Electric cells are essential for providing the energy needed to operate electrical devices and maintain a continuous flow of electric current.
Maharashtra State Board: Class 8

Types of Electric Cells:

1. Dry Cell

A dry cell is a common type of electric cell used in devices like radios, wall clocks, and flashlights. It is simple and convenient, available in different sizes, and can be used in any position.

Dry Cell

Structure and Components,

  • The outer layer is made of zinc (Zn) metal, which serves as the negative terminal.
  • Inside the zinc casing, there is an electrolyte made of a wet pulp containing zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl). This electrolyte carries electricity through charged ions.
  • At the centre of the cell, there is a graphite rod that acts as the positive terminal. Around this rod is a paste of manganese dioxide (MnO₂).

Chemical reactions between the electrolyte and the manganese dioxide produce electric charges on the graphite rod and the zinc layer, creating a flow of electric current. The reactions happen slowly, which means dry cells can’t provide very large currents but are suitable for low-power devices.

2. Lead-Acid Cell

Rechargeable: Can be recharged after losing charge.

  • Contains two electrodes: one made of lead (Pb) and the other of lead dioxide (PbO₂), both immersed in dilute sulphuric acid.
  • The lead dioxide electrode (PbO₂) is positively charged, and the lead electrode (Pb) is negatively charged, creating a potential difference of approximately 2V.
  • Chemical reactions generate charges, causing electric current to flow through connected devices, such as a bulb.

These cells can supply large currents and are used in cars, trucks, motorcycles, and backup power supplies (UPS).

Lead-Acid Cell

3. Ni-Cd Cell (Nickel-Cadmium Cell)

Portable and Rechargeable: Ideal for gadgets that need to be carried around, like cameras and portable electronics.

  • When a nickel-cadmium battery is discharged, it transforms chemical energy into electrical energy, and when it is recharged, it transforms electrical energy back into chemical energy.
  • Provides a potential difference of 1.2V. Commonly used in devices that require frequent charging and portability.
Maharashtra State Board: Class 8

Experiment

1. Aim: To explore the internal structure of a dry cell and understand how it produces electric current.

2. Requirements: A dry cell and tools to remove the outer coating carefully.

3. Procedure

  • Remove the outer coating of a dry cell carefully.
  • Observe the whitish zinc (Zn) layer, which is the negative terminal.
  • Gently break the zinc layer to see the electrolyte, a wet pulp of zinc chloride (ZnCl₂) and ammonium chloride (NH₄Cl) with charged ions.
  • In the centre, locate the graphite rod, the positive terminal, surrounded by manganese dioxide (MnO₂) paste.

Dry Cell

4. Conclusion: The dry cell contains chemicals that react to produce electric charges on the graphite rod and zinc layer, allowing electric current to flow in a circuit. Due to the slow chemical reactions in the wet pulp, the current produced is not very large, but the cell is long-lasting and easy to use in any orientation, making it suitable for portable devices.

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