WJEC PH3 significant figures help

Usually I'm fine with significant figures however I can't seem to get my head around them for PH3 practicals.
I know that you round error to 1sf, so if it is above 10, do you still round it to 1st (e.g. is 14% rounded to 10%?)

Also, there was an experiment that said in the question h=2.0cm. I then gave my readings as 4.5cm, 4.0cm and 5.0 cm but the mark scheme said that answers should be to whole numbers only - why??

Finally, there was an experiment with a 1cm tape and I gave my reading as 8.5cm as the ball landed midway between 8 and 9 however this was wrong - again not sure why

thanks for the help :smile:

Reply 1

TPanda

You cant be give more accurate results than the accuracy of your equipment

Reply 2

Wiggledinho

Original post by TPanda

You cant be give more accurate results than the accuracy of your equipment

so say you had a 1cm scale ruler, your values would have to be 8cm, 9cm etc - they couldn't be 8.5cm?

Reply 3

Wiggledinho

Original post by TPanda

You cant be give more accurate results than the accuracy of your equipment

one other thing, say you measured V to be 1.39V and I to be 0.090A, how many sig figs would you give the calculated resistance to?

Reply 4

TPanda

If the ruler doesnt have mm on it then the reading must be a whole number because the resolution is +-1cm
I tend to give resistance to 2dp but as long as you keep to the sane number of decimal places all through the paper it shouldnt matter too much
Is yours on 1st of May too?

Reply 5

abccba120

How did you guys find it?

Reply 6

buttered_peanut

Original post by Wiggledinho

one other thing, say you measured V to be 1.39V and I to be 0.090A, how many sig figs would you give the calculated resistance to?

3 significant figures. The voltage is measured to 3 s.f. and the current to 4 s.f. so you have to go for the lowest as you can't claim more figures than you read.

How did people find it? I thought A1 was weirdly easy but B4 made my head hurt.

Reply 7

Wiggledinho

Original post by buttered_peanut

all the As were fine I thought but the B was horrific - I always overcomplicate things when they're unfamiliar and so I know that I've lost a lot of marks on that, oh well, I can always retake.

Reply 8

TPanda

I had to do B4 first because of the order of things, my line of best fit isnt perfect, the points are slightly off but do you think tbat would be an issue?

Reply 9

abccba120

Aha i found them alright, although i'm pretty sure i messed up the mass on the unknown weight, i put 0.130g or something like that when it shouldv'e been in kg i think

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Reply 10

Wiggledinho

Original post by abccba120

Aha i found them alright, although i'm pretty sure i messed up the mass on the unknown weight, i put 0.130g or something like that when it shouldv'e been in kg i think

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how did you find B? I thought it was harder than any of the other Bs that I've seen before and I did it wrong - I thought it was quite unclear.

Reply 11

abccba120

I found it alright, the material was constantan i think, just had to show 2 different gradients which represents two different resitivities as gradient was equal to resitivity multiplied by cross sectional area

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Reply 12

Wiggledinho

Original post by abccba120

yeah I also got constantan however where I went wrong was measuring Y as I started from the wrong end of Y and measured it separate to X. Did the board that your wires were on have lines every 10cms for Y? Because my friends said that theirs did, but mine didn't.

Reply 13

abccba120

Hmm not quite sure what you mean but i measured in 20 cm intervals and the total length of wire i got was roughly 1.59m

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Reply 14

Wiggledinho

Original post by abccba120

Hmm not quite sure what you mean but i measured in 20 cm intervals and the total length of wire i got was roughly 1.59m

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I don't know what I mean either haha basically I just panicked and massively over complicated it and ended up getting it wrong but got material right because that was only using wire X so got some of the question right at least...