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ENGINEERING, PPT 2024 HSC 24b

Brushless DC motors are used to power electric-powered bicycles.

Why are these types of motors so well suited to this application?   (3 marks)

Show Answers Only

  • Electronic commutation in brushless DC motors enables straightforward control and enhanced operational efficiency.
  • This precise control of speed and torque makes these motors particularly suitable for e-bike applications.
  • Since there are no brushes to wear down, these motors offer improved durability and longevity.
  • Their ability to deliver substantial torque even at lower speeds gives riders the power they need when starting from a stop or tackling inclines.

Answers could also include the following points:

  • Regenerative braking
  • Efficiency
  • Compact size and lightweight.

Show Worked Solution

  • Electronic commutation in brushless DC motors enables straightforward control and enhanced operational efficiency.
  • This precise control of speed and torque makes these motors particularly suitable for e-bike applications.
  • Since there are no brushes to wear down, these motors offer improved durability and longevity.
  • Their ability to deliver substantial torque even at lower speeds gives riders the power they need when starting from a stop or tackling inclines.

Answers could also include the following points:

  • Regenerative braking
  • Efficiency
  • Compact size and lightweight.
♦ Mean mark 47%.

ENGINEERING, PPT 2018 HSC 21b

Outline the benefits of using electric motors to power self-driving vehicles.   (3 marks)

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Successful engines should include three of the following:

  • Reduced amount of tailpipe emissions through the use of renewable energy as the power source.
  • Lighter engine construction produces a better power to weight ratio.
  • Quieter engines reduce noise pollution.
  • Technology enabling simpler integration into an automated vehicle control system.
  • Less moving parts in electric motors mean they break down less often and need less maintenance.
Show Worked Solution

Successful engines should include three of the following:

  • Reduced amount of tailpipe emissions through the use of renewable energy as the power source.
  • Lighter engine construction produces a better power to weight ratio.
  • Quieter engines reduce noise pollution.
  • Technology enabling simpler integration into an automated vehicle control system.
  • Less moving parts in electric motors mean they break down less often and need less maintenance.

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)

Show Answers Only
  • 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 2019 HSC 23b

An electric scooter is powered by a 12 volt rechargeable battery with a capacity of 18 Ah.

Calculate the energy stored in the battery. Use 1 Wh = 3600 J.   (2 marks)

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`777.6\ text{kJ}`

Show Worked Solution

Power = volts × current

12 V × 18 A × 1 h = 216 W in 1 h

`:.` Power stored = 216 Wh

  
1 W = 1 J/s

1 Wh = 3600 J  (1 h = 60 × 60 seconds)

`:.` Energy stored  = 216 Wh × 3600 J  
   = 777 600 J  
   = 777.6 kJ  
♦ Mean mark 46%.

ENGINEERING, PPT 2020 HSC 26d

The diagram shows an electrical circuit that is used to control the speed of a DC electric traction motor.
 

Explain, with reference to the diagram, how the speed of the motor can be controlled. (3 marks)

Show Answers Only
  • The motor’s speed and torque can be increased or decreased by varying the input current.
  • Since current and resistance are inversely proportional, the current can be increased by decreasing resistance and vice versa.
  • The above diagram shows 4 resistors that can be used or avoided by flicking a switch for each.
  • The more resistors that are switched out of the circuit, the more current flows to the motor and the speed of the motor increases.
Show Worked Solution
  • The motor’s speed and torque can be increased or decreased by varying the input current.
  • Since current and resistance are inversely proportional, the current can be increased by decreasing resistance and vice versa.
  • The above diagram shows 4 resistors that can be used or avoided by flicking a switch for each.
  • The more resistors that are switched out of the circuit, the more current flows to the motor and the speed of the motor increases.

ENGINEERING, PPT 2020 HSC 6 MC

Which electronic component can be used to increase or decrease the speed of a train powered by an electric motor?

  1. Diode
  2. Capacitor
  3. Transistor
  4. Potentiometer
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`D`

Show Worked Solution
  • Potentiometers can act as variable resistors.
  • These can increase or decrease current and therefore adjust the speed of an electric motor.

`=>D`


♦♦♦ Mean mark 20%.

ENGINEERING, PPT 2021 HSC 18 MC

The diagram shows a simplified circuit of an electric scooter.
 

What would be the reading of the ammeter in this circuit?

  1. 3.0 A
  2. 6.0 A
  3. 12.0 A
  4. 26.9 A
Show Answers Only

`C`

Show Worked Solution

Find total resistance (`R_t`):

`1/R_t` `=1/R_1+1/R_2`  
`1/R_t` `= 1/(1+2)+1/3=2/3`  
`R_t` `=3/2 = 1.5\ Ω`  

 
Find current (`I`):

`I=V/R_t=18/1.5=12\ text{A}`

`=>C`

Mean mark 52%.