Higher Technological Studes

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Ok, I'm now getting quite worried about this exam. Not revised enough despite having ages to revise. I need reassured that it will all be fine! :sadnod:

Reply 21

gee:bee

It will be fine.

I reccomend going through the 2007 past paper as many thing tend to go in 2 years after, such as the XOR gate questions and other types.
If you get stuck then grab the answers off the SQA site and see how they did it. That way ou will remember it for tommorow.

Reply 22

ryan1234

how do you do 7b) on 2007 paper? i don't undertstand how they got R1/Rth= 5/1

Reply 23

gee:bee

sorry for the late reply,

7.b) i)

125C Type 6 = 10Kohms

The voltage going into the inverting input of the red comparitor is 5/6x9 = 7.5v

So voltage over R1 must be 7.5v too.
Therefore voltage over thermistor is 1.5v

Using sum of corresponding resistance to voltage;

R1/7.5 = 10/1.5

R1 = 50Kohms.

7b) ii) Lower green voltage at inverting input = 1/6x9 = 1.5v
So voltage at non inverting at turn on is also 1.5v

so there is 1.5v over the 50Kohm resistor that we worked out earlier.
therefore there must be 9-1.5v over the thermistor = 7.5v

using the corresponding resistance/voltage ratio thing;

Rthermistor/7.5 = 50/1.5
Rthermistor = 250Kohms.

I think I made that alot harder for myself but at the end of the day I got the correct answers so :smile:

Reply 24

ryan1234

thanks, but in 7bi) how do you know voltage across R1 is 7.5V too?

Reply 25

MC1

hey, i just found out about this site not long ago. im doing higher tech studies this year aswell and im the only one in my school doing it so ive got to teach it myself so i sometimes find it a bit hard but ive got through it quite well.

its 7.5 because the voltage at inverting is 1.5 so the voltage to change the signal from low to high must also be at least 1.5V at non-inverting, so V at thermistor =9-1.5=7.5
i hope it helped, and good luck for tomorow

Reply 26

void03

curious about that question too
only thing i dont understand is where you are getting the voltage values from?
how/where did you get the 1.5?
'5/6x9 = 7.5v' ~ Where did the 5,6 come from? Im guessing the 9 came from the supply voltage or the rails.

Crashing this subject and the exam is tomorrow XD :woo:

Hope it won't be too hard.

Reply 27

MC1

ah ok, the 5/6 comes from when u calculate the inverting input to the op-amp at the top. its basicly a voltage divider calculation so v= R/Rtotal x Vsupply so substituting it in becomes V=5R2/6R2 x 9 then because "R2" is being divided by "R2" you can remove them making it V=5/6 x 9 = 7.5V. so the inverting input is 7.5V so non-inverting=7.5 v which means that V at R1 is 7.5 v

Reply 28

gee:bee

No.

5/6 are made up values for the same value resistors. for example, you could have said that the 6 identical resistors were 10Kohms each so it would be like 50/60*9

Reply 29

ryan1234

i'll struggle to pass this tomorrow, anybody else feel the same?

Reply 30

keepa7

Just crossing my fingers and hoping questions that i like come up

Reply 31

ryan1234

it was easier than i though it would be :yep:

Reply 32

Jordan131

It wasn't that bad which I'm really pleased about. Could have been much worse.

Reply 33

JONES_12345

I'm happy! :biggrin:

-

It was a lot easier than i thought, there were only 8 questions in the first section, and thats my last exam so they're all over!!

What questions did people do from Section B?

I did 9 and 10. They were good, just about finished in time! And i am glad cos it could have been a lot worse!

I didn't think there were any dodgy questions really! Anyone else think there were?

Reply 34

Jordan131

I did 9 and 10 too. Q11 would require you to understand the situation more it think. Saw a nodal question and one about data logging so went for them straight off. Was finished within 2 hours but spent ages looking over things, spotted a mistake or two.

Reply 35

ik92

i did 10 and 11, the nodal analysis questions were good this year, i think they were my best attemted questions. I missed one or two questions worth about 2-3 marks each but i'm not going to complain because it could of been worse. Hopefully i will achieve atleast a B if not an A.

Reply 36

gee:bee

did anyone remember if they got like
........ _
(C+S).T

for the bolean expression?

ps: please ignore the dots above c+s

Reply 37

Luce14

Last year's exam was difficult but does the exams not get easier for a couple of years after a really difficult exam?
I really struggle with Techy...i got 50 and a half out of 100 in the prelim :s-smilie: