[Systems Engineering Teachers' Mailing List] Practice Exam errors

[Robert Minato]

Had a look at the new practice exam on the vcaa website. There are a few
problems with it:

Section A
Q6. Symbol for a voltage reg is not on the vcaa symbols list. Responses A, B
and D all represent another component, so by default, Response C is left
which must be the correct answer.
Q7. 120 and 600 Ohm in parallel gives 100 Ohms. 12V/100Ohms = 120 mA. No
correct response.
Q11. Brown Green Yellow resistor is 150 kOhms. No correct response.

Section B
Q9. The motor will only ever rotate in one direction. The back emf diode
will be forward biased in one switch position effectively shorting across
the motor. [Depending on the current supply and diode rating, the diode may
burn-out, in which case the motor will then work in the second direction.
Back emf diodes normally used when other components (eg transistor) are in
circuit to prevent damage.]

Formula sheet
The resistor colour code needs a multiplier column. Unless a great deal of
time has been spent with the code, most students would nave some trouble
with the multiplier. Probably explains the confusion with Section A Q11.

Rob


-- 
Robert Minato
Technology Leader
Catholic College Wodonga
1 Bowman Crt
Wodonga 3690
02 6043 5546