Magnetism and Magnetic Induction Flashcards
The angular difference between true north and magnetic north is known as the ________
Angle of declination
________ are magnets that do not require any power or force to maintain their field
Permanent magnets
________ are metals that are easily magnetized, such as iron, nickel, and cobalt
Ferromagnetic materials
________ are metals that can be magnetized, but not as easily as ferromagnetic materials
Paramagnetic materials
True or false: diamagnetic materials are either metal or nonmetal materials that cannot be magnetized
True
Name 3 examples of paramagnetic materials
Platinum, titanium, and chromium
Name 4 examples of diamagnetic materials
Copper, brass, wood, and antimony
Name 4 characteristics of magnetic lines of force
- They form closed loops
- They posses direction
- They repel each other
- They cannot intersect or cross
- Magnetic lines of force represent tension along their length which tends to make them as short as possible
Flux lines are ________ near the poles of a magnet and become ________ as they move further away
Stronger; weaker
Complete the following: A basic law of physics states that whenever an electric current flows through a conductor, ________
A magnetic field is formed around the conductor
________ depend on an electric current flow to produce a magnetic field
Electromagnets
________ is a measure of a material’s ability to become magnetized
Permeability
________ is the property that opposes magnetic flux
Reluctance
________ occurs when all the molecules of the magnetic material are lined up
Saturation
The amount of magnetism left in a material after the magnetizing force has stopped is called _________
Residual magnetism
________ is the amount of magnetizing force necessary to remove residual magnetism from a material
Coercive force
________ is the lagging of the flux density behind the magnetizing force
Hysteresis
When looking at a material’s magnetization curve (hysteresis loop), curves that are tall and narrow are best suited for ________
Electromagnets. A tall and narrow magnetization loop indicates that the material has a high permeability and low retentivity value
A wide and relatively flat curve on a B-H graph indicates that the material would be well suited for use as a ________
Permanent magnet. A wide and flat curve indicates that the material has a high level of residual magnetism (retentivity) and would require a strong coercive force to remove this magnetism
________ refers to the amount of energy lost due to the constant reversal of the magnetic field in an AC circuit
Hysteresis loss
Early natural magnets were known as ________
Lodestones
True or false: The direction of current flow through the wire determines the polarity of the magnetic field
True
Name 3 methods used to demagnetize an object
Placing the object in an AC magnetic field and pulling it away, striking it, and heating it (Curie temperature)
In order for a material to lose it’s magnetism by heat, it must reach a certain temperature known as ________
Curie temperature
True or false: a piece of magnetized material has its molecules in a state of disarray
False. This describes a non-magnetized material. Magnetized materials have their molecules aligned in an orderly pattern
A helically wound coil that produces a strong magnetic field is known as a ________
Solenoid
What is the easiest and most practical method for varying the strength of an electromagnet
Vary the current. Increasing the current will strengthen the electromagnet, decreasing the current will weaken it
A device known as a ________ is used when storing magnets to help prevent their magnetic field from weakening over time
Keeper
________ is a term that refers to the path along which flux lines follow as they form their complete loops
Magnetic circuit
________ refers to the total number of flux lines in a magnetic circuit
Magnetic flux (Q)
Current in an electrical circuit is the equivalent of ________ in a magnetic circuit
Magnetic flux (Q)
The ________ is the unit of magnetic flux and is equal to ________ flux lines
Weber, abbreviated as Wb; 10 to the power of 8 (100,000,000)
________ is the force that causes the setting up of flux lines in a magnetic circuit
Magnetomotive force (Fm)
The magnetomotive force in a magnetic circuit is equal to ________
The number of coil turns in the circuit times the current through the coils (Fm = N x I)
The ________ is the unit of magnetomotive force
Ampere-turn, abbreviated as A.t.
________ is the opposition to the setting up of flux lines in a magnetic circuit
Reluctance (Rm)
Resistance in an electrical circuit is the equivalent of ________ in a magnetic circuit
Reluctance (Rm)
The ________ is the unit of reluctance
Ampere-turn per weber, abbreviated as A.t./Wb
True or false: reluctance in a magnetic circuit increases as the length of the circuit increases, and decreases as the cross-sectional area of the circuit increases
True
________ is the measure of the amount of flux per unit cross section of a magnetic circuit
Flux density (B)
The ________ is the unit of flux density
Tesla, abbreviated as T
________ is the measure of the magnetomotive force per unit length in a magnetic circuit
Magnetizing force (H)
The ________ is the unit of magnetizing force
Ampere-turn per metre, abbreviated as A.t./m
________ is the measure of the ease with which flux may be set up in a unit length and cross section of a material
Permeability (U)
The ________ is the unit of permeability
Weber per ampere-turn metre, or Henries per metre, abbreviated as Wb/A.t.m. or H/m
The permeability of free space (air) is ________
4 pi x 10 to the power of -7
When a coil is wound around a nonmagnetic material such as wood or plastic, it is know as a(n) ________. When a coil is wound around a magnetic material such as iron or soft steel, it is known as a(n) ________
Air-core magnet; iron-core magnet
Like residual magnetism, another term that is used to describe a material’s ability to retain magnetism is ________
Retentivity
Complete the following statement: whenever a conductor cuts through magnetic lines of flux, ________
A voltage is induced in the conductor
Complete the following statement: the polarity of an induced voltage is determined by the ________
Polarity of the magnetic field in relation to the direction of movement
The left-hand rule for current-carrying conductors states that the thumb points in the direction of ________ and the fingers indicate the direction of the ________
Electron flow (current); magnetic field
The left-hand rule for current-carrying coils states that the thumb points to the ________ and the fingers indicate the __________
North pole; direction of electron flow (current)
Name the 3 factors that determine the amount of voltage induced in a conductor
- The number of turns of wire
- The strength of the magnetic field (flux density)
- The speed of the cutting action
In order to induce 1 volt in a conductor, the conductor must cut ________ lines of magnetic flux in ________
100,000,000; 1 second (1 Wb per second)
Lenz’s law states that an induced voltage or current ________
Opposes the motion that causes it
True or false: inductors always oppose a change of current
True
One volt is induced in a conductor when magnetic lines of flux are cut at a rate of ________
1 weber per second
True or false: induced voltage is always opposite in polarity to the applied voltage
True
Two conductors each carrying a current traveling in the same direction will create magnetic fields that ________ one another
Attract
An exponential curve is divided into ________ time constants, with each being equal to ________ of some value
Five; 63.2%
Inductance is measured in units called ________
Henrys (H)
The amount of inductance an inductor will have is determined by the ________ and the ________
Number of turns of wire; physical construction of the coil
According to Faraday’s law of induction, ________ are loops of electrical current induced within conductors by a changing magnetic field in the conductor
Eddy currents
