SKIN EFFECT & FIELDS

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INTRODUCTION

RF energy travels near the surface of conductors. This is referred to as skin effect. The higher the frequency, the thinner the conduction layer under the conductor surface. Consequently, RF resistance can be much higher than DC resistance.

Silver plating is sometimes used to lower resistance for UHF and higher frequencies.

An electromagnetic field is potential energy in the space around a conductor through which a magnetic force acts. Imagine placing the left hand around a conductor with the thumb pointing in the direction of electron flow; the fingers will be in the direction of the magnetic field (left hand rule). The henry is the unit of measure for electrical energy stored in an electromagnetic field.

An electrostatic field is potential energy that exists between the plates of a charged capacitor. The farad is the unit of measure of electrical energy stored in an electrostatic field.

A-001-002-001.... What is the result of skin effect?
  1. as frequency increases, RF current flows in a thinner layer of the conductor, closer to the surface
  2. as frequency decreases, RF current flows in a thinner layer of the conductor, closer to the surface
  3. thermal effects on the surface of the conductor increase impedance
  4. thermal effects on the surface of the conductor decrease impedance
A-001-002-002.... What effect causes most of an RF current to flow along the surface of a conductor?
  1. piezoelectric effect
  2. resonance effect
  3. skin effect
  4. layer effect
A-001-002-003.... Where does almost all RF current flow in a conductor?
  1. in a magnetic field in the centre of the conductor
  2. in a magnetic field around the conductor
  3. along the surface of the conductor
  4. in the centre of the conductor
A-001-002-004.... Why does most of an RF current flow within a very thin layer under the conductor's surface?
  1. because the RF resistance of a conductor is much less than the DC resistance
  2. because of skin effect
  3. because a conductor has AC resistance due to self-inductance
  4. because of heating of the conductor's interior
A-001-002-005.... Why is the resistance of a conductor different for RF currents than for direct currents?
  1. because of skin effect
  2. because of the Hertzberg effect
  3. because conductors are non-linear devices
  4. because the insulation conducts current at high frequencies
A-001-002-006.... What unit measures the ability of a capacitor to store electrical charge?
  1. coulomb
  2. watt
  3. volt
  4. farad
A-001-002-007.... A wire has a current passing through it. Surrounding this wire there is:
  1. a cloud of electrons
  2. a skin effect that diminishes with distance
  3. an electrostatic field
  4. an electromagnetic field
A-001-002-008.... In what direction is the magnetic field oriented about a conductor in relation to the direction of electron flow?
  1. in the direction determined by the left-hand rule
  2. in all directions
  3. in the same direction as the current
  4. in the direct opposite to the current
A-001-002-009.... What is the term for energy that is stored in an electromagnetic or electrostatic field?
  1. potential energy
  2. kinetic energy
  3. ampere-joules
  4. joule-coulombs
A-001-002-010....Between the charged plates of a capacitor there is:
  1. an electrostatic field
  2. a magnetic field
  3. a cloud of electrons
  4. an electric current
A-001-002-011.... Energy is stored within an inductor that is carrying a current. The amount of energy depends on this current, but it also depends on a property of the inductor. This property has the following unit:
  1. coulomb
  2. farad
  3. watt
  4. henry
QUIZ
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