Gibilisco: Chapter 8 - Magnetism

The gauss is a unit of measurement used to quantify magnetic flux density. It represents the amount of magnetic field passing through a specific area. Magnetic flux density refers to the concentration of magnetic field lines within a given space. Therefore, the correct answer is magnetic flux density.

An electromagnet can be switched on and off, unlike a permanent magnet. This is because an electromagnet is created by passing an electric current through a coil of wire, which generates a magnetic field. By controlling the flow of electric current, the strength of the magnetic field can be adjusted or completely turned off. This ability to control the magnetism makes electromagnets more versatile and useful in various applications such as electric motors, generators, and magnetic separators.

The advantage of a magnetic disk over magnetic tape for data storage and retrieval is that data can be stored and retrieved more quickly with disks than with tapes. Magnetic disks have faster access times and can provide random access to data, allowing for quicker retrieval and processing of information. On the other hand, magnetic tapes are sequential access devices, requiring more time to locate and access specific data.

A commutator is a device that reverses the direction of the magnetic field in a DC motor, allowing the motor to continue rotating. It consists of a set of copper segments that are connected to the armature coil. As the armature coil rotates, the commutator brushes make contact with different segments, changing the direction of the current flowing through the coil and therefore reversing the magnetic field. This reversal of the magnetic field ensures that the motor continues to rotate in the same direction.

Lines of magnetic flux are said to originate at a north magnetic pole. This is because a north magnetic pole is a region where the magnetic field lines emerge or start from. Magnetic field lines always form closed loops, and they go from the north pole to the south pole outside the magnet. Therefore, the origin or starting point of these lines is at the north magnetic pole.

A substance with high retentivity is best suited for making a permanent magnet because retentivity refers to the ability of a material to retain its magnetization even after the magnetizing field is removed. Therefore, a substance with high retentivity will be able to maintain its magnetic properties for a longer period of time, making it ideal for creating a permanent magnet that can generate a consistent magnetic field without the need for an external power source.

A material that can be permanently magnetized is generally said to be ferromagnetic. Ferromagnetic materials have strong magnetic properties due to the alignment of their atomic spins. When exposed to a magnetic field, the domains within the material align and create a permanent magnetic field even after the external field is removed. This property makes ferromagnetic materials useful in various applications such as electric motors, transformers, and magnetic storage devices.

The geomagnetic field is what makes a compass work. A compass needle aligns with the Earth's magnetic field, allowing it to point towards the magnetic north pole. This magnetic field is generated by the movement of molten iron in the Earth's outer core. The compass works by utilizing the magnetic properties of the needle and the Earth's magnetic field to determine direction.

The correct answer is "Normally open." In a circuit, a relay is connected in such a way that it allows the device to receive a signal only when the relay coil carries current. A normally open relay means that the circuit is open by default, and it only closes when the relay coil is energized. This configuration ensures that the device connected to the relay only receives a signal when the relay is activated.

A magnetic hard disk is usually part of a computer because it is a storage device used to store and retrieve digital data. It uses magnetic fields to store data on a rotating disk, and it is accessed by a computer's operating system to read and write data. The data stored on a hard disk includes the computer's operating system, software applications, and user files, making it an essential component of a computer system.

The magnetomotive force in ampere-turns is calculated by multiplying the number of turns in the wire coil by the current passing through it. In this case, the wire coil has 10 turns and carries 500 mA of current. Therefore, the magnetomotive force is 10 turns multiplied by 500 mA, which equals 5.0 ampere-turns.

The force between a magnet and a piece of ferromagnetic metal that has not been magnetized is never repulsive. This is because the magnetic field produced by the magnet induces a temporary magnetism in the ferromagnetic material, causing the two to attract each other. Repulsion only occurs when two magnets with the same polarity are brought close together. Since the piece of ferromagnetic metal has not been magnetized, it does not have a magnetic field of its own to repel the magnet.

The correct answer is Tesla. Tesla is the unit of overall magnetic field quantity in the International System of Units (SI). It is named after Nikola Tesla, a renowned physicist and inventor. The Tesla represents the strength of the magnetic field produced by a current-carrying conductor or a magnet. It is defined as one Weber per square meter and is used to measure the magnetic flux density.

Magnetic flux is the measure of the total magnetic field passing through a given area. It can always be attributed to the motion of charged particles. When charged particles move, they create a magnetic field around them. This movement can be in the form of electric current in a wire, electrons orbiting around an atomic nucleus, or the movement of charged particles in space. Therefore, the motion of charged particles is always responsible for the generation of magnetic flux.

The magnetic flux around a straight, current-carrying wire is strongest near the wire. This is because the magnetic field produced by the current-carrying wire follows a pattern of concentric circles around the wire. As you move further away from the wire, the strength of the magnetic field decreases. Therefore, the magnetic flux, which is a measure of the total magnetic field passing through a given area, is strongest near the wire where the magnetic field is most concentrated.

The geomagnetic lines of flux are horizontal at the geomagnetic equator because this is the point where the Earth's magnetic field is parallel to the surface. As you move away from the equator towards the poles, the lines of flux become more vertical. This is because the magnetic field lines converge towards the poles, creating a more vertical orientation. Therefore, at the geomagnetic equator, the lines of flux are horizontal.

A bubble memory is best suited for a large computer because it is a non-volatile memory technology that offers high data storage capacity and fast access times. It is ideal for large-scale data processing and storage requirements of a large computer system. Bubble memory provides reliable and durable data storage, making it suitable for the demanding needs of a large computer.

During a geomagnetic storm, charged particles streaming out from the sun can cause fluctuations in the earth's magnetic field, which can lead to disruptions in electrical power transmission. However, disruption of microwave radio links is not generally possible in a geomagnetic storm. This is because microwave radio links operate at a higher frequency than the disturbances caused by geomagnetic storms, and they are less affected by the fluctuations in the earth's magnetic field.

The magnetomotive force (MMF) in a wire coil can be calculated by multiplying the number of turns in the coil by the current passing through it. In this case, the coil has 100 turns and carries a current of 1.30 A. Multiplying these values gives an MMF of 130 A-turns. However, the unit of MMF is gilberts, not A-turns. To convert A-turns to gilberts, we divide by the constant 1.257. Dividing 130 by 1.257 gives a result of approximately 103.35 gilberts. Therefore, the correct answer is 164 gilberts.

An AC electromagnet will attract pure, unmagnetized iron because when an alternating current passes through the coil of the electromagnet, it creates a changing magnetic field. This changing magnetic field induces a magnetic field in the pure iron, causing it to be attracted to the electromagnet.

A high tape-recorder motor speed is generally used for video because video recording requires a fast motor speed to ensure smooth and uninterrupted playback. The high speed allows for the rapid movement of the tape, resulting in better quality video recordings with minimal distortion or lag. This is particularly important for capturing fast-moving action or scenes with a lot of motion. Using a high motor speed also allows for more data to be recorded on the tape, increasing the storage capacity and allowing for longer video recordings.