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

Understanding the Concept of Electromagnets
When a wire carrying an electric current is wound around a ferromagnetic material, such as an iron nail, it creates a magnetic field. This phenomenon is the basis for what we refer to as an electromagnet.
What is an Electromagnet?
- An electromagnet is a type of temporary magnet that is created when electricity flows through a coil of wire.
- The strength of the magnetic field depends on the amount of current flowing through the wire and the number of turns in the coil.
Why is it Temporary?
- Unlike permanent magnets, which retain their magnetism over time, electromagnets only exhibit magnetic properties while the current is flowing.
- When the current is turned off, the magnetic field disappears, and the material loses its magnetism.
Applications of Electromagnets
- Electromagnets are widely used in various applications, including:
- Electric motors: They allow for the conversion of electrical energy into mechanical energy.
- Magnetic locks: Used for security systems.
- Magnetic cranes: Used in recycling yards to lift heavy metallic objects.
Conclusion
In summary, the correct answer to the question is option C: Electromagnet. This temporary magnet is formed when electric current passes through a coil of wire wrapped around an iron core, demonstrating the principles of electromagnetism.

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.

Understanding Electric Circuit Components
In electric circuits, different components have specific symbols to represent their functions. One such component is the electric cell, which is crucial for providing electrical energy.
Shape and Representation
- An electric cell is depicted with two parallel lines:
- Longer Line: This represents the positive terminal (anode).
- Shorter, Thicker Line: This indicates the negative terminal (cathode).
The Role of an Electric Cell
- Energy Source: The electric cell converts chemical energy into electrical energy, allowing current to flow through the circuit.
- Voltage Generation: The difference in potential between the positive and negative terminals creates voltage, which drives the flow of electric current.
Comparison with Other Components
- Switch: Represents an open or closed circuit but does not have distinct terminal representations.
- Battery: Made of multiple cells, it has a similar representation but typically appears as a combination of multiple lines.
- Bulb: Represents a light-emitting component with a different symbol entirely, usually resembling a circle with a filament.
Conclusion
In summary, the longer line (positive terminal) and the shorter, thicker line (negative terminal) specifically denote an electric cell in an electric circuit. Understanding these symbols is fundamental to analyzing and building electrical circuits.

When a current flows through a wire, it creates a magnetic field around it, causing a nearby compass needle to deflect from its usual north-south alignment.

Function of a Switch in an Electric Circuit
A switch is a fundamental component in an electric circuit, and its primary function is to control the flow of electricity. Here's a detailed explanation:
Opening and Closing the Circuit
- Control of Current Flow: A switch acts like a gate that can either allow or stop the flow of electric current. When the switch is in the "on" position, it closes the circuit, permitting electricity to flow through.
- Turning Devices On and Off: By flipping the switch to the "off" position, the circuit is opened, stopping the current flow. This action turns off any devices connected to the circuit, such as lights or appliances.
Importance in Safety and Functionality
- Safety Mechanism: Switches enhance safety by allowing users to disconnect power easily when needed, reducing the risk of electrical hazards.
- Energy Conservation: By turning off devices when they are not in use, switches help conserve energy and reduce electricity bills.
Types of Switches
- Mechanical Switches: These are the most common types, which require physical movement to operate.
- Electronic Switches: These can control the flow of electricity without moving parts, often used in modern technology.
Conclusion
In summary, the correct answer is option 'C' because the switch's primary function is to open or close the circuit, thereby controlling the flow of electricity. Understanding this function is essential for managing electrical systems safely and efficiently.

Understanding Current Measurement in Electric Circuits
In electric circuits, measuring current is crucial for analyzing circuit performance. The device specifically designed for this purpose is the ammeter.
What is an Ammeter?
- An ammeter is an instrument used to measure the flow of electric current in a circuit.
- It is connected in series with the circuit components to ensure that all the current flowing through the circuit also passes through the ammeter.
Why Choose an Ammeter?
- Direct Measurement: Ammeter provides a direct reading of the current flowing through the circuit in amperes (A).
- Low Resistance: Ammeter is designed with very low internal resistance to minimize its impact on the circuit, ensuring that it does not alter the current it measures.
Comparison with Other Devices
- Voltmeter: Measures voltage (potential difference) across two points in a circuit, connected in parallel. It does not measure current directly.
- Galvanometer: A sensitive device that can detect small currents but is not used for measuring larger currents directly. It can be used to calibrate or convert into an ammeter.
- Resistor: A passive component used to limit current flow or divide voltage but does not measure current.
Conclusion
In summary, the ammeter is the correct choice for measuring current in an electric circuit because of its direct measurement capabilities and design features that allow it to integrate seamlessly into the circuit. Understanding these distinctions helps in selecting the right instrument for electrical measurements.