Electrical Fundamentals Module 3: Magnetism

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Questions and Answers

What happens to the force applied to an electromagnetic coil when it is stretched to twice its length?

The force remains unchanged.

The force is halved. (correct)

The force is doubled.

The force becomes zero.

What is the base unit of magnetic field strength?

Weber per square meter (Wb/m²)

Tesla (T)

Volt per meter (V/m)

Ampere-turn per meter (A.t/m) (correct)

How is magnetic flux density (B) defined?

The strength of the magnetic field over time.

The electrical force required to drive a current through a magnetic circuit.

The total magnetic charge in a coil.

The number of magnetic lines of force through a given area at a right angle. (correct)

What is the primary purpose of placing magnetic material in a magnetic field?

To redirect flux more efficiently Signup and view all the answers

Which type of magnet is produced from material with high reluctance?

Permanent magnet Signup and view all the answers

What is the SI unit for magnetic flux density?

Tesla Signup and view all the answers

What is magnetic flux measured in?

Webers Signup and view all the answers

What does the saturation of a ferromagnetic material indicate?

The material can no longer magnetize further Signup and view all the answers

Which of the following correctly describes the relationship between tesla and gauss?

1 Tesla = 10000 Gauss Signup and view all the answers

What characterizes the hysteresis loop of hard magnetic materials?

Wide loops with high retentivity Signup and view all the answers

How can ferromagnetic materials be magnetized?

By placing them in a strong magnetic field Signup and view all the answers

In magnetic circuits, what does a weber represent?

The change in magnetic flux required to induce one volt in a conductor in one second. Signup and view all the answers

Which of the following describes permeability in terms of magnetism?

The measure of a material's conduction of magnetic lines of force Signup and view all the answers

What is the magnetic field strength (H) calculated from?

Magnetomotive force (MMF) divided by the length of the coil. Signup and view all the answers

What happens to flux density (B) during magnetic hysteresis?

It lags behind changes in magnetizing force (H) Signup and view all the answers

What is a key characteristic of temporary magnets compared to permanent magnets?

They exhibit low reluctance and high permeability Signup and view all the answers

What does the term remanence refer to in ferromagnetic materials?

The degree of magnetic flux density retained after removing the magnetizing force Signup and view all the answers

What is meant by coercivity in the context of magnetic materials?

The reverse driving field required to demagnetize the material Signup and view all the answers

Which type of materials typically exhibit high remanence and high coercivity?

Magnetically hard materials Signup and view all the answers

When does residual magnetism become equal to the retentivity value of a material?

When the material is magnetized to saturation Signup and view all the answers

What is the likely effect of using magnetically soft materials in transformer cores?

They have lower remanence and less stable magnetic performance Signup and view all the answers

In the context of electromagnetic fields, what does hysteresis relate to?

The time delay in the magnetic response of a material to an applied field Signup and view all the answers

What is the primary characteristic of soft materials in terms of their magnetic loops?

They exhibit narrow loops Signup and view all the answers

Which statement best describes the role of current flowing through a wire in relation to magnetic fields?

It produces a circular magnetic field around the wire. Signup and view all the answers

What effect do adjacent molecular magnets have on un-magnetised material?

They neutralise each other's forces. Signup and view all the answers

What is the primary condition that characterizes magnetised material?

Most molecular magnets aligned in one direction. Signup and view all the answers

What principle does Domain Theory primarily depend on?

Electron spin. Signup and view all the answers

What occurs to an atom when equal numbers of electrons spin in opposite directions?

The atom remains un-magnetised. Signup and view all the answers

In Weber's Theory, what happens when a steel bar is stroked by a magnet?

The magnetic force aligns the molecules. Signup and view all the answers

How many protons does an iron atom contain in its nucleus?

26 Signup and view all the answers

What consequence does having more electrons spinning in one direction than the other have on an atom?

The atom is magnetised. Signup and view all the answers

What is the likelihood of an atom being un-magnetised if the number of spinning electrons is equal in both directions?

Very likely. Signup and view all the answers

Where is the magnetic axis of the Earth located in relation to its geographical axis?

About 15° from the geographical axis Signup and view all the answers

What is the primary function of a compass in relation to magnetic poles?

To align with the Earth's magnetic field Signup and view all the answers

What does the law of magnetic poles state about the interaction between poles of a magnet?

Like poles repel, unlike poles attract Signup and view all the answers

How are magnetic lines of force represented in relation to a magnet?

They emanate from the North pole and enter the South pole Signup and view all the answers

What is the common misconception about the term 'North Pole' in relation to a magnet?

It has the same polarity as the Earth's magnetic North Pole Signup and view all the answers

Which statement accurately describes the directional alignment of a freely suspended bar magnet?

It aligns in a north-south direction Signup and view all the answers

What phenomenon occurs when two identical poles of magnets are brought near each other?

They repel each other Signup and view all the answers

What key characteristic of magnetic lines of force helps in understanding magnetic fields?

They provide a method to visualize the strengths of magnets Signup and view all the answers

What type of materials are typically used to create artificial magnets?

Special iron or steel alloys Signup and view all the answers

Which characteristic best defines permanent magnets?

Difficult to magnetize but retain significant magnetism Signup and view all the answers

What property of materials makes temporary magnets easy to magnetize but difficult to retain magnetism?

Low reluctance Signup and view all the answers

What is the term for the amount of magnetism that remains in a temporary magnet after the magnetizing force has been removed?

Residual magnetism Signup and view all the answers

How would you describe the magnetic field surrounding a magnet?

Concentrated at the ends and weak at the center Signup and view all the answers

What determines whether a magnet is classified as permanent or temporary?

The ability to retain magnetism after removing the magnetizing force Signup and view all the answers

What does the term 'retentivity' refer to in the context of magnets?

The ability of a material to retain an amount of residual magnetism Signup and view all the answers

Which of the following materials would likely make a good temporary magnet?

Soft iron Signup and view all the answers

What does the term 'permeability' refer to in magnetism?

The ability of a material to support the formation of a magnetic field within itself Signup and view all the answers

What characterizes the coercive force in magnetic materials?

The measure of how much magnetic field strength is needed to demagnetize a material Signup and view all the answers

Which of the following describes the concept of 'magnetic shielding'?

The reduction of magnetic field exposure within a certain area Signup and view all the answers

What does the 'saturation point' refer to in magnetic materials?

The point at which a material can no longer be magnetized further Signup and view all the answers

Which term describes the loops created during a material's magnetization and demagnetization process?

Hysteresis loop Signup and view all the answers

What is the main principle behind capacitor discharge magnetisers?

They produce a brief but very strong magnetic field from a quick pulse of high current. Signup and view all the answers

What method can be used to demagnetize low carbon steel?

Heating the material above its curie temperature. Signup and view all the answers

How can the demagnetization of a component be achieved using an alternating magnetic field?

By slowly withdrawing the magnet from the field or reducing the field strength. Signup and view all the answers

What is the result of hammering or jarring a magnet?

It randomizes the magnetic domains, potentially leaving some residual magnetization. Signup and view all the answers

Which material is most practical for magnetization using standard methods?

Alnico or small sections of ceramic materials. Signup and view all the answers

What is the purpose of employing magnetic shielding in electric instruments?

To prevent magnetic fields from influencing sensitive mechanisms. Signup and view all the answers

How does the strength of the magnetic field around a wire change with distance from the wire?

It diminishes with distance. Signup and view all the answers

What happens to a component when it is subjected to a reversing and decreasing magnetic field?

It undergoes demagnetization. Signup and view all the answers

Which of the following is NOT a method for demagnetization?

Submerging in a liquid nitrogen bath. Signup and view all the answers

What rule helps determine the direction of the magnetic field around a conductor?

Left-Hand Grasp Rule Signup and view all the answers

What is the effect on two parallel conductors carrying current in the same direction?

They will attract each other. Signup and view all the answers

How does coiling a wire affect its magnetic field strength?

It strengthens the magnetic field. Signup and view all the answers

In the Left-Hand Grasp Rule, what does the thumb represent?

Direction of current flow Signup and view all the answers

What happens to the magnetic field when two conductors are placed parallel to each other?

They can either attract or repel depending on current direction. Signup and view all the answers

Which of the following statements about conductors is true when current is flowing?

The magnetic field exists only while current is flowing. Signup and view all the answers

What is true about the direction of the magnetic field when looking at the end of a conductor?

It can be determined using the Left-Hand Rule. Signup and view all the answers

Study Notes

Module 3: Electrical Fundamentals, Topic 3.10: Magnetism

Magnetism is essential for understanding electricity
Magnetism and electricity are closely related
Most electrical and electronic equipment relies on magnetism
Examples include computers, video equipment, high-fidelity speakers, and electrical motors
Two main theories of magnetism exist: Weber's and Domain
Weber's theory suggests that tiny molecular magnets within a material align to create a magnetic effect. Unmagnetized materials have randomly aligned molecular magnets. Magnetized materials have aligned molecular magnets
Domain theory suggests that the electron spin within atoms causes magnetism. Equal numbers of electrons spinning in opposite directions cancel out magnetic fields, creating unmagnetized atoms. Unequal spin generates magnetic domains, and when aligned, creates a magnetized material
Materials that are easily magnetized are called ferromagnetic materials (iron, steel, cobalt)
Alloys - Alnico and Permalloy - can be strongly magnetized
Natural magnets were known by the ancient Greeks, referred to as lodestones
Ancient Greeks also used magnetism to create compasses
Modern artificial magnets are generally made from special iron or steel alloys and are often magnetized electrically
Artificial magnets can be permanent or temporary, depending on their ability to maintain magnetism after the magnetizing force is removed
Permanent magnets are difficult to magnetize and retain most of their magnetism
Temporary magnets are easy to magnetize but lose their magnetism relatively quickly
Magnetic poles are the areas where magnetic force is concentrated
Like poles repel, unlike poles attract
Magnetic lines of force exist in the area surrounding a magnet
They do not actually exist but are used to illustrate the pattern of the magnetic field
The lines of force emanate from the north pole and enter the south pole
The Earth is a large natural magnet with a magnetic axis that is roughly 15° off its geographical axis
The magnetic north pole is actually a south pole, attracting the north pole of a compass
Electromagnets are magnets that are produced by using electric current in a coil of wire
The field intensity of an electromagnet depends on several factors, such as core material, coil size and shape, number of turns on the coil, and the amount of current flowing through the coil
Demagnetization occurs when magnetic domains are randomly reoriented by methods like heating above a material's curie temperature, or by placing the material in a strong reversing magnetic field
Magnetic shielding is achieved by placing a material of high permeability in the affected area
Magnetomotive force (MMF) is the ability of an electric current to create a magnetic field in a magnetic circuit
This is analogous to electromotive force in an electrical circuit
The standard unit of MMF is the ampere-turn (AT)
The strength of a magnetic field depends on how much current, or how many turns, in the coil driving the field.
Eddy current is a microscopic current flowing within a conductor when a conductor passes through a changing magnetic field. This can generate heat
The methods for measuring magnetic flux density and magnetomotive force are described
Basic electromagnets and their operation are described
Information about the care and storage of magnets is provided

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Description

Explore the foundational concepts of magnetism related to electrical fundamentals. This quiz covers the theories of magnetism, including Weber's and Domain theories, and their applications in various electrical and electronic devices. Understand the significance of magnetism in technology such as motors and speakers.