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ENGINEERING, PPT 2024 HSC 25b

A circuit diagram is shown.
 

Use Ohm's Law to determine the current in the circuit.   (3 marks)

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\(I= 0.57\ \text{Amps}\)

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\(E=IR\ \ \Rightarrow\ \ I=\dfrac{E}{R}\)

\(R_{\text{total}} = 10\ \Omega + \dfrac{1}{\dfrac{1}{20\ \Omega} + \dfrac{1}{25\ \Omega}} = 21.11\ \Omega \)

\(I=\dfrac{E}{R} = \dfrac{12\ \text{V}}{21.11\ \Omega} = 0.57\ \text{Amps}\)

ENGINEERING, PPT 2018 HSC 7 MC

An arrangement of resistors is shown.
 

What is the total resistance of this arrangement of resistors?

  1. `33 Omega`
  2. `50 Omega`
  3. `150 Omega`
  4. `300 Omega`
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`C`

Show Worked Solution
`R_(text{total})` `=R_(text{parallel}) + 100 Omega`  
`1/(R_(text{parallel}))` `= 1/R_1 + 1/R_2= 1/50`  
`R_(text{parallel})` `= 50 Omega`  

 
`:. R_(text{total})= 50 + 100= 150 Omega`

   
`=>C`

ENGINEERING, PPT 2018 HSC 22d

To operate successfully, a laser diode requires 2.3 V while drawing a current of 25 mA.
 

For the circuit shown, calculate the required resistor value `R` needed to produce the correct operating voltage.   (3 marks)

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`268\ text{Ohms}`

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`V= V_(\text{total})-V_(\text{led})= 9-2.3= 6.7\ text{V}`

`R= V/I= 6.7\(25 xx 10^(-3))= 268\ text{Ohms}`


♦ Mean mark 43%.

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)

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  • 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 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
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`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%.