All questions of Electric Current and Its effects for Class 7 Exam

When a bulb gets fused, it indicates that the filament inside has failed. Here’s a detailed explanation of what happens:
What Happens to the Filament?
- The filament is made of a thin wire, typically tungsten, that is designed to glow when electric current passes through it.
- When the current flows, the filament heats up and emits light.
- Over time, due to continuous heating and cooling, the filament becomes weak.
Breaking of the Filament
- Eventually, the filament can no longer withstand the stress and heat.
- It breaks, leading to an open circuit, which means electricity can no longer flow through the bulb.
- This results in the bulb no longer lighting up, known as the bulb being ‘fused.’
Why Does This Happen?
- Factors like high voltage, frequent switching on and off, and manufacturing defects can contribute to the filament breaking.
- The breakage often occurs at the point where the filament is the thinnest, making it more susceptible to breaking.
Conclusion
- When a bulb fuses, the filament is indeed broken (Option A).
- This is a common occurrence and indicates that the bulb needs to be replaced for proper functionality.
Understanding this process helps in grasping the basic principles of electrical circuits and components.

Understanding the Filament in a Light Bulb
When electricity passes through the filament of a light bulb, several fascinating processes occur.
1. Heating Effect of Electricity
- When electric current flows through the filament, it encounters resistance.
- This resistance causes the filament to heat up significantly.
2. Incandescence
- As the filament reaches high temperatures (usually around 2000 to 3000 degrees Celsius), it begins to glow.
- This phenomenon is known as incandescence, where the filament emits visible light due to its heat.
3. Light Production
- The intense heat excites the atoms in the filament, causing them to emit photons, which are particles of light.
- This is why the light bulb shines brightly.
4. Material of the Filament
- Most light bulb filaments are made from tungsten due to its high melting point and ability to withstand extreme temperatures without melting.
5. Efficiency and Lifespan
- Traditional incandescent bulbs are not very energy-efficient as a lot of energy is lost as heat rather than light.
- However, they are simple in design and have been widely used for many years.
In summary, when electricity flows through the filament of a light bulb, it heats up and produces light through the process of incandescence. This transformation from electrical energy to light energy is what makes light bulbs an essential part of our daily lives.

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.

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.

An ammeter is a measuring device used to measure the electric current in a circuit. A voltmeter is connected in parallel with a device to measure its voltage, while an ammeter is connected in series with a device to measure its current.

Introduction
In electrical wiring, different wires are used for different purposes to ensure the safe and efficient flow of electricity. One of the most commonly used wires is the one with black insulation. This wire is known as the neutral wire. In this response, we will explain why the wire with black insulation is usually the neutral wire in electrical wiring.

Understanding Electrical Wiring
Electrical wiring is a system that consists of various components, including wires, switches, outlets, and circuit breakers. These components work together to distribute electricity from the main power source to different appliances and devices in a building or a house. The wiring system is designed to ensure the safe transmission of electrical energy.

The Neutral Wire
The neutral wire is an essential part of electrical wiring. It is a current-carrying conductor that provides a return path for the electrical current back to the source. In most electrical systems, the neutral wire is connected to the earth ground, creating a low-resistance path for fault currents to flow. This helps protect people and property from electrical shocks and reduces the risk of electrical fires.

Identification of the Neutral Wire
To identify the neutral wire, electrical codes and standards have established a color-coding system for insulation. In this system, the neutral wire is usually identified by black insulation. However, it is important to note that this color-coding may vary in different regions or countries. Therefore, it is always recommended to consult local electrical codes and standards for accurate identification.

Other Types of Wires
While the wire with black insulation is typically the neutral wire, there are other types of wires used in electrical wiring. These include:

1. Live Wire: The live wire carries the current from the power source to the electrical devices. It is usually identified by red or brown insulation. The live wire is the wire that poses the greatest risk of electrical shock and should be handled with caution.

2. Earth Wire: The earth wire, also known as the grounding wire, provides a path for electrical faults to flow safely into the ground. It is typically identified by green or green/yellow insulation. The earth wire is crucial for protecting against electrical faults and ensuring the safety of the electrical system.

3. Fuse Wire: Fuse wire is not a type of wire used in regular electrical wiring. It refers to a thin wire inside a fuse that melts when excessive current flows through it. This breaks the circuit and protects the electrical system from overloading or short circuits.

Conclusion
In electrical wiring, the wire with black insulation is usually the neutral wire. It provides a return path for the electrical current and is connected to the earth ground. Proper identification of wires is essential for the safe and effective functioning of electrical systems. It is important to adhere to local electrical codes and standards for accurate identification and installation of wires.