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25072 version 1
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Demonstrate knowledge of electromagnetism theory
Level 2
Credits 5
Purpose This unit standard covers knowledge of electromagnetism theory which
underpins all technical careers in the electrical and electronic industries.
People credited with this unit standard are able to demonstrate knowledge of:
– magnets and magnetism;
– a.c. generation;
– d.c. generation; and
– the simple d.c. motor.
Subfield Electrical Engineering
Domain Core Electrical
Status Registered
Status date 22 August 2008
Date version published 22 August 2008
Planned review date 31 December 2010
Entry information Open.
Replacement information This unit standard, unit standard 25070, and unit
standard 25071 replaced unit standard 15843.
Accreditation Evaluation of documentation by NZQA and industry.
Standard setting body (SSB) ElectroTechnology Industry Training Organisation
Accreditation and Moderation Action Plan (AMAP) reference 0003
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.
New Zealand Qualifications Authority 2010
25072 version 1
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2 This unit standard is one of three designed to cover knowledge of magnetism and
electricity, the others being Unit 25070, Explain the properties of conductors,
insulators, and semiconductors and their effect on electrical circuits and Unit 25071,
Demonstrate knowledge of electromotive force (e.m.f.) production. It is
recommended that competency in unit standards 25070 and 25071 be achieved
before assessment against this unit standard is attempted.
3 Definitions
a.c. – alternating current.
d.c. – direct current.
e.m.f. – electromotive force.
r.m.s. – root-mean-square.
4 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 (p) 10-12 ;
nano (n) 10-9; micro (μ) 10-6; milli (m) 10-3; kilo(k) 103; mega (M) 106; etc) and to
be able to convert between them.
5 Formulae quoted in this unit standard use internationally recognised symbols and
units.
6 Conventional current flow direction (positive to negative) is implied. Trainees should
be aware of the opposite direction of electron flow.
Elements and performance criteria
Element 1
Demonstrate knowledge of magnets and magnetism.
Performance criteria
1.1 Magnetic terms are explained in relation to permanent magnets, in accordance
with industry practice.
Range permanent magnet, magnetic field strength, lines of force,
magnetic poles, magnetic flux, flux density.
1.2 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.
1.3 The construction of an electromagnet is described with the aid of a sketch
indicating current direction and magnet polarity.
New Zealand Qualifications Authority 2010
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1.4 The transformer principle is explained in terms of induced e.m.f. resulting from
changing flux linkages.
1.5 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.
1.6 The purpose and application of magnetic screening is stated in terms of
protection of sensitive meters and circuitry from magnetic interference.
Element 2
Demonstrate knowledge of a.c. generation.
Performance criteria
2.1 The operation of a simple single-loop, two-pole alternator with slip-rings and
brushes is described with the aid of a sketch.
2.2 Alternator output for each quarter-cycle through one revolution is described with
the aid of a sketch, and shows a completed resultant waveform.
2.3 A.c. terms are defined in accordance with industry practice.
Range cycle, period, frequency, peak, average, instantaneous, r.m.s.
2.4 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.
2.5 Values are calculated from a.c. voltage and current wave form data.
Range peak, average, r.m.s., frequency, period.
Element 3
Demonstrate knowledge of d.c. generation.
Performance criteria
3.1 The induction of an e.m.f. in a conductor being moved in a magnetic field is
demonstrated using Fleming's right-hand rule.
3.2 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.
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3.3 Generator output for each quarter-cycle through one revolution is described and
shows a completed resultant waveform.
Element 4
Demonstrate knowledge of the simple d.c. motor.
Performance criteria
4.1 The direction of the force exerted on a current carrying conductor in a magnetic
field is determined using any popular rule.
Range any popular rule may include but is not limited to – Fleming's left-
hand rule.
4.2 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.
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.
Comments on this unit standard
Please contact the ElectroTechnology Industry Training Organisation
reviewcomments@etito.co.nz if you wish to suggest changes to the content of this unit
standard.
New Zealand Qualifications Authority 2010
