Electromagnetism Lecture Notes Review

This set of flashcards covers key concepts, definitions, and principles from the lecture on Electromagnetism, providing a comprehensive study tool for the upcoming exam.

What is the primary focus of electromagnetism?

The relationship between electricity and magnetism.

Who discovered that a magnetic compass needle would turn near a wire carrying direct current?

Hans Oersted.

What are lodestones?

Natural magnets that attract pieces of iron.

List the four types of magnetic materials.

Ferromagnetic, paramagnetic, diamagnetic, and nonmagnetic.

What is ferromagnetic material characterized by?

Strong attraction to magnets and the alignment of magnetic dipoles.

What distinguishes paramagnetic materials?

Slight attraction to magnets and inability to become permanently magnetized.

How do diamagnetic materials respond to magnetic fields?

Weakly repelled by all magnetic fields.

Give examples of nonmagnetic materials.

Wood, glass, rubber, and plastics.

What is a magnetic field?

The space surrounding a magnet or moving electric current where magnetic forces are detectable.

What creates a magnetic field around an atom?

The orbital movement of electrons around the nucleus.

What are the two poles of a magnet called?

North pole and south pole.

What happens to a magnet when it is divided?

Each piece retains both north and south poles.

Define permeability in the context of magnetism.

The ease with which a material can become magnetized by an external magnetic field.

What does retentivity refer to?

The ability of a material to retain its magnetism over time.

What dictates the direction of the current flow in a motor?

The direction of the magnetic field created by the armature.

What principle do electric motors operate on?

The law of repulsion and attraction.

How does electromagnetic induction work?

Induction of current in a conductor by a changing magnetic field.

Describe mutual induction.

Occurs when a varying current in one coil induces a current in a nearby coil.

What is self-induction?

The phenomenon where an induced emf creates a current opposing the original current.

What device converts mechanical energy to electrical energy?

Electric generator.

Define electromagnet. What distinguishes it from other magnets?

A temporary magnet created by electric current, with no retentivity once electricity is turned off.

What are slip rings used for in AC generators?

To maintain constant contact with the rotating conductor.

What type of current do generators produce during operation?

Alternating current (AC).

How does a DC generator differ from an AC generator?

DC generators use a commutator ring instead of slip rings.

What kind of materials are commonly used in the construction of generators and motors?

Conductive materials like copper and ferromagnetic materials.

State Faraday's law of electromagnetic induction.

The magnitude of the induced emf depends on the magnetic field strength, the motion relative to the magnetic field, the angle, and the number of turns in the coil.

What role does the commutator play in a DC motor?

It ensures that the current direction is switched to maintain continuous motion of the armature.

What are the components of an induction motor?

A rotor and a stator.

How does an electric generator physically induce current?

By moving a conductor through a magnetic field.

What type of current does a self-induction process generate?

Current that moves in the opposite direction of the original emf.

How does the addition of iron to a coiled conductor affect its magnetic strength?

It increases the magnetic field strength by concentrating the field lines.

Describe the importance of magnetic domains.

Groups of aligned atoms that create a net magnetic field in materials.

What is the effect of distance on magnetic force according to the inverse square law?

The force decreases with the square of the distance between magnets.

List examples of ferromagnetic materials.

Iron, nickel, and cobalt.

What determines the strength of an induced current in a conductor?

The strength and speed of the changing magnetic field.

Explain the term 'magnetic domain' in simple terms.

Tiny magnets within a material whose direction can align to create a stronger magnet.

How do magnetic field lines behave around a magnet?

They flow from the north pole to the south pole outside the magnet and vice versa inside.

What happens to a ferromagnetic material in the absence of an external magnetic field?

It maintains a random orientation of domains with no net magnetism.

What is the significance of the magnetic field in MRI technology?

It's essential for producing images based on the magnetic properties of tissues.

State the effect of heating a magnet.

It can destroy its magnetism by randomizing the orientation of domains.

What material is often used in MRI contrast agents?

Gadolinium, a paramagnetic material.

How does the arrangement of electrons in ferromagnetic materials influence their magnetism?

Electrons' spins are predominantly aligned in the same direction, creating magnetic dipoles.

What defines a solenoid?

A coiled conductor that creates a magnetic field when an electric current passes through it.

In what way do motors and generators convert energy?

Motors convert electrical energy into mechanical energy; generators convert mechanical energy into electrical energy.

What factor allows a magnet to be recombined after being broken?

Each piece possesses its own north and south pole.

What is the relationship between line density of magnetic field lines and strength?

More concentrated lines indicate a stronger magnetic field.

Name the law governing the relationship between magnetic poles.

Like poles repel; unlike poles attract.

What happens in a transformer?

Mutual induction occurs between coils to transfer electrical energy.

Describe how electric fields are affected by magnetic fields.

A changing magnetic field creates an electric field, inducing current flow.

What type of material is highly magnetic and retains some magnetism?

Permanent magnets are often made from alloys designed for high retentivity.

What is the primary role of the rotor in an induction motor?

To follow the alternating current’s changing magnetic field.

In terms of x-ray machines, how are induction motors used?

They drive the rotating anode by converting electrical energy into mechanical motion.

What is one unique feature of a magnetic dipole?

It behaves like a tiny magnet with a distinct north and south pole.

What does 'cutting field lines' refer to in electromagnetic induction?

It describes the motion of conductors through magnetic fields to induce current.

How do changes in conductor speed through a magnetic field affect induced current?

Faster speeds lead to higher induced current due to more field lines being crossed.

When is a magnetic field produced in an electric generator?

When the armature moves through the magnetic field lines.

What determines the direction of movement in an electric motor?

The direction of the magnetic forces acting on the armature.

How does an electromagnet function in an imaging system?

It creates strong magnetic fields essential for digital imaging processes.

What are the visual representations of magnetic fields called?

Magnetic field lines.

Explain why ferromagnetic materials can become permanent magnets.

Their domains can be aligned and maintained in a uniform direction.

What is the general consequence of increasing the number of turns in a coil?

It increases the magnitude of the induced emf.

Define the purpose of the stator in an AC induction motor.

It provides the changing magnetic field needed for rotor movement.

What is one key difference between alternating current and direct current?

AC changes direction periodically, while DC flows in one direction.

Name the magnetic material that is weakly attracted and retains no magnetism.

Paramagnetic material.

What is a common characteristic of diamagnetic materials?

They are weakly repelled by magnetic fields.

Describe the role of brushes in a generator.

To maintain electrical connection with the slip rings while allowing rotation.

Why must certain materials be avoided in MRI rooms?

To prevent interference with the magnetic fields used in imaging.

In what scientific domains has electromagnetism significantly influenced development?

In fields such as medical imaging, telecommunications, and electrical engineering.

What does the frequency of alternating current dictate in an electrical system?

The rate at which the current oscillates back and forth.

What happens to cancerous cells in MRI scans?

They exhibit different magnetic properties compared to healthy tissues.

How do changing magnetic fields produce voltage in a new environment?

Through induction in conductors placed within those fields.

What critical principle helps to understand magnetic levitation in various applications?

The interaction between opposing magnetic fields.

Explain the significance of electromagnetic induction in modern technology.

It's fundamental to the operation of transformers, motors, and generators.