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ENGINEERING, TE 2023 HSC 25b

Explain the functions of a transistor in an electrical circuit.  (3 marks)

 

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→ One transistor function is to act as an amplifier. It magnifies a signal by allowing a current to flow from the emitter to the collector when a small current passes through the base.

→ A transistor can also operate as a switch. In this capacity, it allows current to flow or not, depending on whether certain conditions are satisfied.

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→ One transistor function is to act as an amplifier. It magnifies a signal by allowing a current to flow from the emitter to the collector when a small current passes through the base.

→ A transistor can also operate as a switch. In this capacity, it allows current to flow or not, depending on whether certain conditions are satisfied.

♦♦ Mean mark 36%.

ENGINEERING, TE 2018 HSC 22c

The following three types of diode are used in telecommunication circuits.
 

Describe the function of each diode in telecommunication circuits.   (4 marks)

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Zener diode

→ Voltage regulator.

→ Allows current to flow above an assigned voltage (zener voltage).

→ Stable reference voltage for a range of current values.
 

Laser diode

→ Focused light beam produced when current present in the circuit.

→ Pulses of light transmitted down optical fibre, allowing transmission of digital data.
 

Light emitting diode

→ When current present in the circuit a wide beam of light is emitted.

→ Frequently used so show power is on.

Show Worked Solution

Zener diode

→ Voltage regulator.

→ Allows current to flow above an assigned voltage (zener voltage).

→ Stable reference voltage for a range of current values.
 


♦♦ Mean mark 39%.

Laser diode

→ Focused light beam produced when current present in the circuit.

→ Pulses of light transmitted down optical fibre, allowing transmission of digital data.
 

Light emitting diode

→ When current present in the circuit a wide beam of light is emitted.

→ Frequently used so show power is on.

ENGINEERING, TE 2019 HSC 26b

A simple circuit diagram of the AM radio receiver is shown.
 

  1. Complete the table giving the function of each of the circuit components listed.   (5 marks)
     

  1. Complete the table by drawing the waveform at positions B and C.   (2 marks)
     

  1. This AM radio receiver produced a demodulated electrical signal with a small current. The speakers in the earphones converted this signal into sound.
  2. Explain why the speakers in the earphones required a high impedance (resistance) in order to produce sound of sufficient volume to be heard.   (2 marks)
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i.  


♦ Mean mark (i) 47%.

ii.  


♦♦♦ Mean mark (ii) 22%.

iii.   → An external power source is not used to power this radio.

→ The signal picked up by the aerial powers the speakers.

→ If the impedance (resistance) is high an audible signal can be generated by the speaker at a low current.

→ Because the earphone impedance is high, the sensitivity of the coil improves, resulting in a more accurately tuned signal.

→ The sound would be inaudible if the impedance is low, as the power to the earpiece would also be low.


♦♦♦ Mean mark (iii) 15%.