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2003 Q6 - HSN forum

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2003 Q6


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#1 Pyrefly

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Posted 15 May 2006 - 02:40 PM

Well i was going through the multiple choice part of the 2003 paper (ended up getting 17/20 for it tongue.gif) but i just didn't even know where to start with Question 6.

so er...help would be nice ^^

#2 Michael

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Posted 15 May 2006 - 02:50 PM

Its just one of those learning outcomes you have to know. Answer C

#3 Pyrefly

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Posted 15 May 2006 - 03:07 PM

*hunts for sheets* hmm...i dont remeber reading it...just as well i did this question to realise i had no idea ;p

Thanks smile.gif

ok...had a look through my notes...i cant see anything about the change in density/ distance in spacing between molecules when a gas changes to a liquid sad.gif

Anyone have a site that i can read up on that?

(i've never really been great on gas laws/pressure/density stuff)

bah my stupid notes.....

#4 Michael

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Posted 15 May 2006 - 03:19 PM

http://www.bbc.co.uk/scotland/education/bi...att/index.shtml

That might have some smile.gif. Im sure its in the sqa notes, if you look up their arrangements you might find it.

#5 Pyrefly

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Posted 15 May 2006 - 03:27 PM

QUOTE
When a liquid changes into a gas, the spacing between the particles increases by a factor of about ten. As such, because the volume of a substance is length × breadth × height, the volume will increase by a factor of 1000.

As a result, the density of a substance decreases by a factor of approximately 1000 when it changes from a liquid to a gas.


I was a little confused as i could only see thet density of water was roughly 1000 times that of air. I wasn't sure if the same applied for any "gas" as the question asked for. smile.gif

thanks for your help

#6 Michael

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Posted 15 May 2006 - 03:37 PM

No problem, glad I could help smile.gif

#7 skint_student

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Posted 15 May 2006 - 05:27 PM

as a general rule gas molecules are approximatley 10 times further apart than in liquids and solids. So there for the volume will be (10 x 10 x 10) = 1000 times greater. And finally the density will be 1000 times smaller.
You just need to learn that.

#8 methzzz

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Posted 15 May 2006 - 07:08 PM

Yes when a solid/liquid changes to a gas the particles are approx. 10 times further appart. that makes the density 1000 times greater, as (10 length x 10breadth x 10 height)

#9 Adam

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Posted 15 May 2006 - 09:45 PM

QUOTE(Pyrefly @ May 15 2006, 03:40 PM) View Post

Well i was going through the multiple choice part of the 2003 paper (ended up getting 17/20 for it tongue.gif) but i just didn't even know where to start with Question 6.

so er...help would be nice ^^

Seeing as you obviously know this stuff... can you please explain how you got #7, #10 and #11? smile.gif

#10 Michael

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Posted 15 May 2006 - 09:54 PM

7. Gas is released so pressure decreases as the gas was compressed. The volume wil remain constant as air will fill the place of the gas. Mass will decrease as mass of air is less than that of gas. Answer = E

10. Use the rule for parallel resistor to find the bottom branch has a resistance of 20. Then use ratios i.e bottom hold 1/3 of V supply to find V=4. Answer = E

11.As light level decreases resistance increases so V=IR for the LDR is greater. This means the LDR takes a greater share of the voltage and the other resistor takes less. Answer = D

#11 Pyrefly

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Posted 16 May 2006 - 07:29 AM

er..ya what he said tongue.gif

7 was one i got wrong though. Thanks for asking so i could see the answer too ;p

10. 1/Rt = 1/R1 + 1/R2 (for the parallel part at the bottom)
that should make the resistance of that part 20 ohms.

Then its just the whole ratio thingy. 20:40 = 1:2
divide the Vs of 12 by 3 (3 from the ratio) and thats your answer biggrin.gif
(not that you couldn't see it from Dhesi's answer)

11. As the light shone on the LDR decreases the resistance increases. This means a greater amount of the voltage supply is given to given to the LDR. V1 decreases V2 increases.

#12 ermd

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Posted 16 May 2006 - 07:43 AM

QUOTE(Dhesi @ May 15 2006, 10:54 PM) View Post

11.As light level decreases resistance increases



QUOTE(Pyrefly @ May 16 2006, 08:29 AM) View Post

11. As the light is shone on the LDR the resistance increases


Well, one of you is wrong. rolleyes.gif

#13 Pyrefly

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Posted 16 May 2006 - 10:01 AM

whoops...was typing a little fast..missed out the word decreases tongue.gif
(the question wasx talking about the light decreasing...forgot to mention that when explaining ;p)


(Its all to do with the electron holes and light causeing more holes meaning more current can pass through the reverce baised diode...ya best look at you notes instead of reading this as revision ;p)





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