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Subel. A
6 questions
Subelement A

Principles

Section 2

Magnetism

What determines the strength of the magnetic field around a conductor?

  • The resistance divided by the current.
  • The ratio of the current to the resistance.
  • The diameter of the conductor.
  • Correct Answer
    The amount of current.

What determines the strength of the magnetic field around a conductor?

The amount of current

The amount of current describes the movement of electrons, expressed in amperes.

Magnetic fields can be described as how far its strength extends, measured in amperes per meter, A/m, or H.

The other term related to the magnetic field is the magnetic flux which measures how strong the magnetic force is, and expressed as Newtons per meter per amperes, or T (Teslas).

For more info, please see Wikipedia's article on Magnetic field.

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What will produce a magnetic field?

  • A DC source not connected to a circuit.
  • The presence of a voltage across a capacitor.
  • Correct Answer
    A current flowing through a conductor.
  • The force that drives current through a resistor.

What will produce a magnetic field?

A current flowing through a conductor.

The amount of current describes the movement of electrons, expressed in amperes.

Magnetic fields can be described as how far its strength extends, measured in amperes per meter, A/m, or H.

The other term related to the magnetic field is the magnetic flux which measures how strong the magnetic force is, and expressed as Newtons per meter per amperes, or T (Teslas).

For more info, please see Wikipedia's article on Magnetic field.

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When induced currents produce expanding magnetic fields around conductors in a direction that opposes the original magnetic field, this is known as:

  • Correct Answer
    Lenz’s law.
  • Gilbert's law.
  • Maxwell’s law.
  • Norton’s law.

When induced currents produce expanding magnetic fields around conductors in a direction that opposes the original magnetic field, this is known as:

Lenz’s law.

Above a good definition of this law.

For solid info to understand, please see Wikipedia's article on Lenz's law

Highly recommend watching YouTube videos:

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The opposition to the creation of magnetic lines of force in a magnetic circuit is known as:

  • Eddy currents.
  • Hysteresis.
  • Permeability.
  • Correct Answer
    Reluctance.

The opposition to the creation of magnetic lines of force in a magnetic circuit is known as:

Reluctance.

The above is a good simple definition.

For more info, please see Wikipedia's article on Magnetic reluctance

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What is meant by the term “back EMF”?

  • A current equal to the applied EMF.
  • An opposing EMF equal to R times C (RC) percent of the applied EMF.
  • Correct Answer
    A voltage that opposes the applied EMF.
  • A current that opposes the applied EMF.

What is meant by the term “back EMF”?

A voltage that opposes the applied EMF.

From johnnymac:

Back-EMF (Electromotive Force), is most commonly used to refer to the voltage that occurs in electric motors where there is relative motion between the armature of the motor and the magnetic field from the motor's field magnets, or windings.

MNEMONIC: Remember "E" stands for voltage.

For more info, please see Physics LibreText site for the article 13.7: Electric Generators and Back Emf

Also, see the Wikipedia's article Counter-electromotive force

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Permeability is defined as:

  • The magnetic field created by a conductor wound on a laminated core and carrying current.
  • Correct Answer
    The ratio of magnetic flux density in a substance to the magnetizing force that produces it.
  • Polarized molecular alignment in a ferromagnetic material while under the influence of a magnetizing force.
  • None of these.

Permeability is defined as:

The ratio of magnetic flux density in a substance to the magnetizing force that produces it.

In electricity, permeability refers to how big the magnetic field around the core is, being dependent on the amount of current supplied. This is called the magnetic flux, or how strong the magnetic substance is.

For more info, please see Wikipedia's article on Permeability (electromagnetism)

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