Test: Electricity and Magnetism - Class 7 MCQ

The contact spring in an electric bell serves to break the circuit once the armature moves towards the electromagnet. This interruption in the current causes the electromagnet to lose its magnetism, allowing the armature to return to its original position, thus creating the ringing sound as the process repeats.

Magnetic keepers are used for bar magnets to prevent loss of magnetism. By placing a soft iron piece across the ends of the magnet, the magnetic field is closed, which helps maintain the magnet's strength over time. This practice is essential for preserving the effectiveness of permanent magnets.

A permanent magnet retains its magnetism even after the external force that magnetized it is removed. This property allows permanent magnets to be used in everyday items like refrigerator magnets, speakers, and various types of sensors. Materials such as steel are commonly used to create permanent magnets.

The unit of electric current is the ampere (A). It measures the flow of electric charge over time, specifically how many coulombs of charge pass through a conductor in one second. This unit is fundamental in electrical engineering and physics.

In a series circuit, the current remains the same throughout all components. However, the total resistance increases with the addition of more resistors. This means that if one component fails (e.g., a bulb burns out), the entire circuit is interrupted, and all components will stop working.

The quantity of electric charge is represented by the symbol C, which stands for coulombs. This unit quantifies the amount of electric charge that flows in a circuit, and it is defined based on the flow of approximately 6.25 × 10^18 electrons.

Increasing the number of turns in the coil of an electromagnet enhances its strength. This is because more turns create a stronger magnetic field when electric current flows through the coil. The relationship between the number of turns and the strength of the magnetic field is a key principle in electromagnetism.

Like poles of magnets, such as north-north or south-south, repel each other due to the magnetic forces at play. This principle is essential for understanding magnet interactions and is often demonstrated in classroom experiments involving bar magnets.

Resistance in an electric circuit serves to hinder the flow of electric current. It is a measure of how much a material opposes the passage of current, and it is crucial for controlling the flow of electricity in various devices. For example, in a light bulb, the resistance of the filament causes it to heat up and emit light when current flows through it.

A solenoid primarily functions to convert electrical energy into mechanical energy. When electric current flows through the coil of wire, it generates a magnetic field that can exert force on a movable core or armature, making it useful in various applications, including electromagnetic switches and valves.

A natural magnet is defined as one that exists in nature without human intervention, such as magnetite, which is an ore of iron. In contrast, artificial magnets are crafted by humans. Natural magnets can exhibit significant magnetic properties, but their strength can vary compared to artificial magnets, which are often engineered for specific uses.

An electromagnet is a type of magnet that is generated through the flow of electric current. It consists of a solenoid (a coil of wire) with an iron core that becomes magnetized when electricity flows through it. This property allows electromagnets to be used in various applications such as electric bells and motors, making them highly versatile and useful.

In a parallel circuit, if one component fails, only that specific component stops working, while the other components continue to operate normally. This design allows for greater reliability in electrical systems, as the failure of one part does not disrupt the entire circuit.

Rubber is classified as a bad conductor of electricity, meaning it does not allow electric current to flow through it efficiently. This characteristic makes rubber an excellent insulator, which is why it is commonly used to coat electrical wires to prevent accidental shocks.

A magnetic compass is a navigational instrument that helps users find directions by utilizing the earth's magnetic field. The compass needle aligns itself with the magnetic north, allowing sailors and pilots to determine their heading accurately. This technology has been crucial for navigation for centuries.

Heating a magnet can cause it to lose its magnetism. The heat energy can disrupt the alignment of the magnetic domains within the material, leading to a decrease in its magnetic strength. This is why magnets should be handled with care and kept away from high temperatures.

A resistor's primary role in an electric circuit is to limit the flow of current. By providing resistance, it helps control the amount of current that can pass through a circuit, ensuring that components operate within their safe limits and preventing damage.

According to Ohm's Law, electric current is inversely proportional to resistance in a circuit. This means that as resistance increases, the current decreases if the voltage remains constant. This relationship is represented by the formula I = V/R, where I is current, V is voltage, and R is resistance.

When the electric current flowing through an electromagnet is turned off, it loses its magnetism. Electromagnets are temporary magnets that only exhibit magnetic properties while electric current is present. This characteristic is utilized in various devices, such as relays and solenoids.

When an electric current flows through a wire, it generates a magnetic field around the wire, causing a nearby magnetic needle to align itself with the direction of the magnetic field. This phenomenon illustrates the relationship between electricity and magnetism, as demonstrated in Oersted's experiment.