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ENGINEERING, TE 2025 HSC 21a

An engineer needs to analyse signal strength in communications cabling over time.

Describe a device that the engineer could use in testing signal strength.   (2 marks)

Show Answers Only
  • A cathode ray oscilloscope (CRO) is a device used to measure and display signal strength in communications cabling.
  • It displays voltage over time, showing waveform shape, frequency, peak voltage and any signal interference or loss.
Show Worked Solution
  • A cathode ray oscilloscope (CRO) is a device used to measure and display signal strength in communications cabling.
  • It displays voltage over time, showing waveform shape, frequency, peak voltage and any signal interference or loss.

ENGINEERING, TE 2017 HSC 7 MC

Wireless networks operate in two distinct frequency bands: 2.4 GHz and 5 GHz.

Which of the following statements is correct?

  1. 5 GHz waves experience lower attenuation and have a lower bandwidth
  2. 5 GHz waves experience higher attenuation and have a higher bandwidth
  3. 2.4 GHz waves experience lower attenuation and have a higher bandwidth
  4. 2.4 GHz waves experience higher attenuation and have a lower bandwidth
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`B`

Show Worked Solution
  • Lower frequencies (2.4GHz) are characterised by lower bandwidth but also good range coverage due to their lower attenuation.
  • Higher frequencies such as 5GHz are subject to higher attenuation especially when they encounter solid objects.

`=>B`


♦♦ Mean mark 38%.

ENGINEERING, TE 2018 HSC 16 MC

Four output graphs from an oscilloscope are shown.
 

   

   

Which graph(s) represent direct current (DC)?

  1. Graph 4 only
  2. Graphs 3 and 4 only
  3. Graphs 2,3 and 4 only
  4. Graphs 1, 2 and 3 only
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`C`

Show Worked Solution
  • For the current to be DC, the output has to be only positive or only negative, not a mix of both, as this represents alternating current.
  • Hence graphs 2, 3 and 4 represent DC.

`=>C`


♦♦♦ Mean mark 21%.

ENGINEERING, TE 2022 HSC 25a

Describe how an insulation test is performed on electrical cabling.   (3 marks)

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  • The primary method of testing insulation is the use of a megohmmeter.
  • The megohmmeter is connected across the material to be tested and applies a test voltage for a sample period of around 60 seconds.
  • This allows the device to detect the amount of current leakage, measured in ohms.
Show Worked Solution
  • The primary method of testing insulation is the use of a megohmmeter.
  • The megohmmeter is connected across the material to be tested and applies a test voltage for a sample period of around 60 seconds.
  • This allows the device to detect the amount of current leakage, measured in ohms.

♦♦ Mean mark 39%.

ENGINEERING, TE 2022 HSC 22c

An engineer is selecting a suitable material for the exterior housing of a telecommunications device such as the smart watch. Justify material properties that should be considered.   (3 marks)

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Properties to be considered:

  • Hardness: To resist abrasions/scratches encountered in daily life
  • Toughness: To resist damage from sudden impacts such as falling over
  • Water resistance: Protect internal electronics from exposure to water
  • Hypoallergenic: Avoid damage to user’s skin
  • Corrosion resistance and chemical stability: Increase lifespan of smartwatch and prevent injury to user
Show Worked Solution

Properties to be considered:

  • Hardness: To resist abrasions/scratches encountered in daily life
  • Toughness: To resist damage from sudden impacts such as falling over
  • Water resistance: Protect internal electronics from exposure to water
  • Hypoallergenic: Avoid damage to user’s skin
  • Corrosion resistance and chemical stability: Increase lifespan of smartwatch and prevent injury to user

ENGINEERING, TE 2021 HSC 24b

Outline how voltage can be tested in a circuit.   (2 marks)

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Successful answers should cover one of the following testing methods:

Voltmeter

  • A voltmeter is placed across 2 points in a circuit in parallel, and measures the potential difference/voltage between these points.
  • The voltmeter does not interfere with the current in the circuit, as its high resistance draws minimal current.

Multimeter

  • The probes of a multimeter can be used to measure voltage by testing the potential difference between 2 points, as with a voltmeter.  

Oscilloscope

  • Use its probes to measure voltage.
  • Give additional information regarding current and wavelength.
  • Visually represent this data in graphical form.
Show Worked Solution

Successful answers should cover one of the following testing methods:

Voltmeter

  • A voltmeter is placed across 2 points in a circuit in parallel, and measures the potential difference/voltage between these points.
  • The voltmeter does not interfere with the current in the circuit, as its high resistance draws minimal current.

Multimeter

  • The probes of a multimeter can be used to measure voltage by testing the potential difference between 2 points, as with a voltmeter.  

Oscilloscope

  • Use its probes to measure voltage.
  • Give additional information regarding current and wavelength.
  • Visually represent this data in graphical form.

Mean mark 53%.
COMMENT: A surprisingly low result here warrants attention.