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Aussie Maths & Science Teachers: Save your time with SmarterEd

ENGINEERING, PPT 2017 HSC 15 MC

What can be used to minimise significant losses in electrical power transmission cables?

  1. Very high current
  2. Very high voltage
  3. Very high resistance
  4. Very high capacitance
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`B`

Show Worked Solution
  • Power losses are proportional to square of the current in an electrical transmission.
  • Hence if the current is kept to a minimum then losses are minimised.
  • To keep the current low the transmission has to be at high voltage as per Ohms Law.

`=>B`

ENGINEERING, PPT 2016 HSC 22b

Describe TWO methods of generating electricity.   (3 marks)

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Successful answers should include two of the following:

  • Traditional power generation – Steam is generated through heated water in steam turbines which turn a generator to produce electricity.
  • Solar power generation – Electric potential is generated through photosensitive diodes when exposed to light.
  • Other technologies using turbines to produce electricity include hydorelectric, tidal flow and wind power.
Show Worked Solution

Successful answers should include two of the following:

  • Traditional power generation – Steam is generated through heated water in steam turbines which turn a generator to produce electricity.
  • Solar power generation – Electric potential is generated through photosensitive diodes when exposed to light.
  • Other technologies using turbines to produce electricity include hydorelectric, tidal flow and wind power.

ENGINEERING, PPT 2019 HSC 26a

The photograph shows an AM radio coupled to a pedal-powered generator. This radio allowed communication in remote areas of Australia during the 1920s.
 

Explain how the mechanical energy from pedalling was converted into electrical energy in the generator to power the AM radio.   (3 marks)

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  • A generator consists of a magnet surrounded by a coil of wire.
  • Pedalling causes the magnet to spin and electricity is produced within the coil through magnetic induction.
  • The radio transceiver is powered by the generated electrical energy.
  • As the generator’s speed increases so does the voltage supplied.
Show Worked Solution
  • A generator consists of a magnet surrounded by a coil of wire.
  • Pedalling causes the magnet to spin and electricity is produced within the coil through magnetic induction.
  • The radio transceiver is powered by the generated electrical energy.
  • As the generator’s speed increases so does the voltage supplied.

ENGINEERING, PPT 2020 HSC 23c

The diagram shows a dynamo mounted on the frame of a bicycle, with its roller positioned against the side of the tyre. Wires connect the dynamo to the bicycle light.
 

Explain how the dynamo generates power to turn the bicycle light on.   (3 marks)

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  • When the wheel on the bicycle begins turning, the shaft (connected to the roller) spins the armature through a magnetic field produced by stationary magnets.
  • This process, with the effect of the commutator, results in the generation of DC electricity.
  • Wires connecting the dynamo to the light carry the DC electricity to the light, turning it on.
Show Worked Solution
  • When the wheel on the bicycle begins turning, the shaft (connected to the roller) spins the armature through a magnetic field produced by stationary magnets.
  • This process, with the effect of the commutator, results in the generation of DC electricity.
  • Wires connecting the dynamo to the light carry the DC electricity to the light, turning it on.

♦ Mean mark 48%.

ENGINEERING, PPT 2021 HSC 22c

An electric skateboard battery is rated at 0.078 watts at an operating voltage of 48 volts.

Calculate the capacity of the battery in amp hours, if it fully discharges in one hour of use. The power (`P`) is given by the formula  `P=V I`.    (3 marks)

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`text{Capacity} = 5.85\ text{Ah}`

Show Worked Solution

`text{Power = 0.078 W,  Volts = 48 V}`

`P` `=VI`
`I` `=P/V=0.078/48`

 
`:.\ text{Capacity}=(0.078×3600)/48=5.85\ text{Ah}`


♦ Mean mark 50%.