15843 Demonstrate knowledge of magnetism and electricity by 4T2tc7

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Demonstrate knowledge of magnetism and electricity

Level                             2

Credits                           15

Purpose       This unit standard covers knowledge of basic magnetism and electricity
              which underpins all technical careers in the electrical and electronic
              industries.

              People credited with this unit standard are able to: demonstrate knowledge of
              electrical conductors, insulators, and semiconductors, resistance, resistivity,
              and resistors; compare calculated with measured values in resistive circuits;
              demonstrate knowledge of electrical power and energy; analyse resistive
              circuits; and demonstrate knowledge of electromotive force (e.m.f.)
              production, electrochemistry, magnets and magnetism, and direct current
              (d.c.) and alternating current (a.c.) generation.


Subfield                           Electrical Engineering

Domain                             Core Electrical

Status                             Expiring

Status date                        22 August 2008

Date version published             22 August 2008

This unit standard is expiring. Assessment against the standard must take place
before the expiry date set out below.

Expiry date                        31 December 2014

Entry information                  Recommended: Mathematics and Technology subjects
                                   to Level 6 of the New Zealand Curriculum.

Replacement information            This unit standard has been replaced by unit standard
                                   25070, unit standard 25071, and unit standard 25072.

                                   This unit standard replaced unit standard 741, unit
                                   standard 742, unit standard 744, unit standard 746, unit
                                   standard 747, and unit standard 756.

Accreditation                      Evaluation of documentation by NZQA and industry.

Standard setting body (SSB)        ElectroTechnology Industry Training Organisation

Accreditation and Moderation Action Plan (AMAP) reference                   0003



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This AMAP can be accessed at http://www.nzqa.govt.nz/framework/search/index.do.

Special notes

1     This unit standard has been designed for learning and assessment off-job.

2     For assessment purposes
      a Candidates shall be supplied with formulae involving more than three quantities.
      b Use of a calculator during assessment is permitted.
      c Candidates are expected to express calculated values in the relevant Systeme
        Internationale (SI) units, including multiples and sub-multiples (pico, nano, micro,
        milli, kilo, mega, etc) and be able to convert between them.

3     Formulae quoted in this unit standard use internationally recognised symbols and
      units.

Elements and performance criteria
Element 1

Demonstrate knowledge of electrical conductors, insulators, and semiconductors.

Performance criteria

1.1        The nature of conductors, insulators, and semiconductors is described in terms
           of their atomic structure.

           Range         conductors – loosely-bound valence electrons;
                         insulators – tightly-bound valence electrons;
                         semiconductors – sharing of valence electrons.

1.2        Materials commonly used for conductors, insulators and semiconductors are
           identified, and their orders of resistance stated.

           Range         conductors – copper, brass, silver, gold, aluminium, steel;
                         insulators – rubber, polyvinyl chloride (PVC), ceramics;
                         semiconductors – silicon and germanium, intermediate nature of
                         semiconductors between conductors and insulators, with
                         opportunities for change in either direction.

1.3        Typical uses of conductors and insulators are stated.

           Range         evidence of three uses for conductors and three uses for
                         insulators is required.




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1.4       Conductor and insulator materials suitable for given environmental conditions
          are identified, and reasons for their suitability are stated.

          Range         conductors – copper, silver, aluminium, tungsten, carbon,
                        nichrome, brass;
                        insulators – glass, mica, oil, ceramics, rubber, PVC;
                        environmental conditions – heat, moisture, corrosive materials,
                        dust, tension, compression, vibration.
                        Evidence is required of one conductor and one insulator material
                        for each environmental condition.

Element 2

Demonstrate knowledge of resistance, resistivity, and resistors.

Performance criteria

2.1       Resistance is described in terms of opposition to current flow.

2.2       The unit for resistance is stated, and the symbol drawn.

2.3       The factors affecting resistance and the relationships between them are stated.

          Range         factors – length, cross-sectional area, resistivity of material,
                        temperature, temperature co-efficient of resistance;
                                            l
                        relationship – R      .
                                             A

2.4       Linear and non-linear resistors are briefly described with reference to their
          construction, operating characteristics, symbols, connections, and applications.

          Range         linear resistors include – carbon, metal film, wire-wound, slider
                        potentiometer, rotary carbon potentiometer, rotary rheostat;
                        non-linear resistors include – negative temperature co-efficient
                        (NTC) thermistor, positive temperature co-efficient (PTC)
                        thermistor, voltage dependent resistor (VDR), light dependent
                        resistor (LDR).
                        Evidence of two linear and two non-linear resistors is required.

2.5       The meanings of the terms tolerance, preferred values, stability, power rating,
          power dissipation, voltage rating, and current rating, as used in connection with
          resistors, are stated.

2.6       Resistor markings relating to resistance, rating, and tolerance are interpreted.

          Range         evidence of three different linear resistors is required. Use of
                        resistor colour code chart is permitted.

2.7       Ohm's Law is defined in accordance with industry practice.




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2.8       The relationship between resistance, voltage, and current is described in terms
          of the effect that a change in any one quantity has on the other two.

2.9       The concept of insulation resistance of a cable is explained in terms of typical
          values and the effect of cable length.

2.10      Insulation resistance is calculated for a specified length of cable, from the
          known insulation resistance of a different length of the same cable.

Element 3

Compare calculated with measured values in resistive circuits.

Range     circuits – series, parallel and series-parallel combinations of up to five
          resistances, a single source of e.m.f., internal resistance;
          values – resistance, applied e.m.f., volt-drop, current, power.

Performance criteria

3.1       Values are calculated for a given circuit.

3.2       Values are measured for the same circuit and compared to calculated values.

3.3       Variations between measured and calculated values are explained in terms of
          component tolerance, supply variations, non-linear components, instrument and
          measurement error.

Element 4

Demonstrate knowledge of electrical power and energy.

Performance criteria

4.1       Electrical power is defined in terms of voltage, current, and resistance, and its
          unit and symbol are stated in accordance with industry practice.

4.2       Total power, and power in individual resistors, are calculated from given data for
          series circuits, parallel circuits, and series-parallel circuits.

4.3       Electrical energy is defined in terms of power and time taken, and its units and
          symbols are stated in accordance with industry practice.

4.4       The relationship between mechanical energy and power, and electrical energy
          and power is demonstrated in terms of the equivalence of watt-seconds to
          joules, conversion of kilowatt-hours to joules, and vice versa.

4.5       Horsepower values are converted to kilowatts, and vice versa.

4.6       Efficiency is described in terms of the relationship between input and output
          powers of electrical machines.




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4.7        Quantity and cost of energy are calculated from given data for a simple
           domestic loading, and expressed in kilowatt-hours and dollars.

Element 5

Analyse resistive circuits.

Range      resistive circuits – one source of electromotive force (e.m.f.), up to five
           resistances connected in any combination, one internal resistance.

Performance criteria

5.1        Kirchhoff's Laws for voltage and current are defined in accordance with industry
           practice.

5.2        The total resistance of a circuit is calculated from resistor values.

5.3        The current flowing in any part of the circuit is calculated and Kirchoff's current
           law verified.

5.4        The voltage across any two points in the circuit is calculated and Kirchoff's
           voltage law verified.

Element 6

Demonstrate knowledge of electromotive force (e.m.f.) production.

Range      chemical, magnetic, friction, piezo-electric, photo-electric, thermocouple.

Performance criteria

6.1        Methods of producing an e.m.f. are briefly described in terms of how it is
           achieved and the relative magnitude of the voltage produced.

6.2        An example of a common device using each method of generation is stated.

Element 7

Demonstrate knowledge of electrochemistry.

Performance criteria

7.1        The construction and operation of a primary cell and of a lead-acid battery are
           described with the aid of labelled sketches.

           Range         the descriptions and diagrams should reflect an understanding of
                         the terms – primary cell, secondary cell, battery, electrolyte,
                         specific gravity, electrodes, cathode, anode, charging, discharging;
                         details of chemical reactions are not required.

7.2        Battery capacity is defined in terms of current and time.




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7.3      The characteristics and typical applications of cells in common use are stated.

         Range         cells – lead-acid, nickel-iron, nickel-cadmium, mercury;
                       characteristics – size, nominal voltage, typical capacity, primary or
                       secondary.

7.4      Precautions that ensure safe charging of lead-acid batteries are stated in
         accordance with industry practice.

7.5      Situations where electrical energy creates a chemical effect are stated.

         Range         electroplating, corrosion.

7.6      Electrochemical corrosion is described in terms of electrode potentials between
         metals and electrolytic action of surroundings.

7.7      Methods of reducing corrosion are stated.

         Range         methods – alloying, protective coatings, cathodic protection,
                       neutralising of environment.

Element 8

Demonstrate knowledge of magnets and magnetism.

Performance criteria

8.1      Magnetic terms are explained in relation to permanent magnets, in accordance
         with industry practice.

         Range         permanent magnet, magnetic field, lines of force, magnetic poles,
                       magnetic flux, flux density.

8.2      The direction of the magnetic field surrounding a current carrying wire is
         determined using any popular rule.

         Range         any popular rule may include but is not limited to – the right-hand
                       screw rule.

8.3      The construction of an electromagnet is described with the aid of a sketch
         indicating current direction and magnet polarity.

8.4      The direction of the force exerted on a current carrying conductor in a magnetic
         field is determined using Fleming's left-hand rule.

8.5      The operation of a simple motor is explained with the aid of a sketch showing
         direction of current and polarity of the magnet.

         Range         simple motor – permanent magnet, single loop of wire, two-
                       segment commutator, carbon brush.




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8.6       The transformer principle is explained in terms of induced e.m.f. resulting from
          changing flux linkages.

8.7       Devices using electromagnetic and magnetic properties are described in simple
          terms.

          Range        any two of – loudspeaker, relay, electric bell, moving coil
                       instrument, lifting magnet, electric door lock.

8.8       The purpose and application of magnetic screening is stated in terms of
          protection of sensitive meters and circuitry from magnetic interference.

Element 9

Demonstrate knowledge of d.c. generation.

Performance criteria

9.1       The induction of an e.m.f. in a conductor being moved in a magnetic field is
          demonstrated using Fleming's right-hand rule.

9.2       The operation of a simple direct current generator is explained with the aid of a
          sketch.

          Range        simple generator – permanent magnet, single loop of wire, two-
                       segment commutator, carbon brush.

9.3       Generator output for each quarter-cycle through one revolution is described and
          shows a completed resultant waveform.

Element 10

Demonstrate knowledge of a.c. generation.

Performance criteria

10.1      One cycle of a sine wave is plotted from values.

          Range        plot sine versus angle at 30-degree intervals, or construct
                       graphically using instantaneous values from a rotating quantity.

10.2      The operation of a simple single-loop, two-pole alternator with slip-rings and
          brushes is described with the aid of a sketch.

10.3      Alternator output for each quarter-cycle through one revolution is described with
          the aid of a sketch, and shows a completed resultant waveform.

10.4      A.c. terms are defined in accordance with industry practice.

          Range        cycle, period, frequency, peak, average, instantaneous, root-
                       mean-square (r.m.s.).




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10.5      The reason for using the r.m.s. value of an a.c. wave form is stated in terms of
          the equivalence of r.m.s. and steady d.c. values for resistive heating effect.

10.6      Values are calculated from a.c. voltage and current wave form data.

          Range         peak, average, r.m.s., frequency, period.

Please note

Providers must be accredited by NZQA, or an inter-institutional body with delegated
authority for quality assurance, before they can report credits from assessment against
unit standards or deliver courses of study leading to that assessment.

Industry Training Organisations must be accredited by NZQA before they can register
credits from assessment against unit standards.

Accredited providers and Industry Training Organisations assessing against unit standards
must engage with the moderation system that applies to those standards.

Accreditation requirements and an outline of the moderation system that applies to this
standard are outlined in the Accreditation and Moderation Action Plan (AMAP). The
AMAP also includes useful information about special requirements for organisations
wishing to develop education and training programmes, such as minimum qualifications for
tutors and assessors, and special resource requirements.




                                                               New Zealand Qualifications Authority 2012

								
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