All questions of Current Electricity and Magnetism for Class 8 Exam

Function of a Battery in an Electric Circuit
A battery plays a crucial role in an electric circuit by serving as a source of energy. Here’s a detailed explanation of its function:
1. Energy Storage
- Definition: A battery stores electrical energy in the form of chemical energy.
- Mechanism: When a battery is charged, it undergoes a chemical reaction that allows it to store energy. When the circuit is closed (connected), this stored energy is released as electrical energy to power devices.
2. Power Supply
- Continuous Energy Flow: The battery provides a continuous flow of electricity until its stored energy is depleted.
- Voltage Source: It maintains a specific voltage, which is essential for the functioning of electrical devices.
3. Portability and Versatility
- Easy to Use: Batteries are portable, making them suitable for a wide range of applications, from small gadgets to larger systems.
- Versatile Applications: They are used in everything from remote controls to electric vehicles.
4. Importance in Circuits
- Enabling Functionality: Without a battery, most electronic devices would not function, as they require a source of power to operate.
- Safety and Control: Batteries allow for controlled energy release, which is vital for the safe operation of electronic devices.
In summary, the primary function of a battery in an electric circuit is to store electricity, which can then be converted into usable energy for various applications. This makes it an essential component in modern technology.

Introduction to Oersted's Discovery
Hans Christian Oersted, a Danish physicist, made a groundbreaking discovery in 1820 that linked electricity and magnetism, laying the foundation for electromagnetism.
Oersted's Experiment
- Oersted conducted a simple yet profound experiment using a compass and a current-carrying wire.
- He noticed that when an electric current flowed through a wire, the compass needle nearby deflected from its usual north-south orientation.
Significance of the Discovery
- This deflection indicated that an electric current produces a magnetic field around the wire.
- It was the first demonstration of the connection between electricity and magnetism, which was revolutionary for science.
Impact on Science
- Oersted's findings paved the way for future research in electromagnetism, influencing scientists like Michael Faraday and James Clerk Maxwell.
- It led to the development of various technologies, including electric motors and generators, which are essential in today's world.
Conclusion
- Hans Christian Oersted's discovery was crucial in understanding the relationship between electricity and magnetism.
- His work continues to inspire and impact various fields in physics and engineering, making him a key figure in the history of science.

The Symbol of an Electric Cell
In the representation of an electric cell, the lengths of the lines play a crucial role in identifying the terminals.
Understanding the Lines
- Longer Line: Represents the positive terminal (anode).
- Shorter Line: Represents the negative terminal (cathode).
Why the Longer Line is Positive
- Conventional Current Flow: In electrical circuits, conventional current is defined as flowing from the positive terminal to the negative terminal. This is why the longer line is designated as positive.
- Symbol Standards: These conventions have been standardized in electrical diagrams to ensure consistency and clarity. The longer line helps users quickly identify which terminal is which.
Importance in Circuits
- Correct Connections: Understanding which terminal is positive is critical for connecting cells correctly in series or parallel configurations.
- Safety: Misidentifying the terminals can lead to short circuits or damage to electrical components.
Conclusion
In summary, the longer line in the symbol of an electric cell indicates the positive terminal, while the shorter line indicates the negative terminal. This distinction is vital for understanding how electrical circuits function and ensuring safe and effective use of electrical components.

Why MCBs are Preferred Over Traditional Fuses
When it comes to electrical safety and efficiency, Miniature Circuit Breakers (MCBs) hold several advantages over traditional fuses. The key reason for this preference lies in their ability to automatically switch off during overloads.
Automatic Switching Off
- MCBs are designed to detect faults in the circuit, such as overloads or short circuits.
- When an overload occurs, the MCB automatically trips and disconnects the circuit, preventing potential damage to electrical devices and reducing fire risks.
Convenience and Reusability
- Unlike traditional fuses, which need to be replaced once blown, MCBs can simply be reset after they trip.
- This feature saves time and effort, as users do not need to keep spare fuses on hand.
Faster Response Time
- MCBs react much quicker to faults compared to fuses, providing better protection for electrical appliances.
- This rapid response minimizes damage to devices, enhancing their lifespan and reliability.
Enhanced Safety
- MCBs not only protect against overloads but also protect against short circuits, making them a more comprehensive safety solution.
- This dual protection significantly lowers the risk of electrical hazards in homes and workplaces.
In summary, the preference for MCBs over traditional fuses is primarily due to their ability to automatically switch off during overloads, providing enhanced safety, convenience, and efficiency in electrical systems.