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how was physics paper 21

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Agassi Cazaubon

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arlery said:
and that only happens when emf in one cell is equal to the one in another. :/
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.. That would kinda defeat the point of the potential divider though if you were using two cells of equal emf.. then there would be no need to shift the pointer to get a galvanometer reading of 0.. it would already be 0 at the maximum distance.. you're trying to find the emf.. you get to the point where no current is flowing so that you can ignore the internal resistance of the cell and find an accurate value for emf..
 
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nahid842

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Agassi Cazaubon said:
.. That would kinda defeat the point of the potential divider though if you were using two cells of equal emf.. then there would be no need to shift the pointer to get a galvanometer reading of 0.. it would already be 0 at the maximum distance.. you're trying to find the emf.. you get to the point where no current is flowing so that you can ignore the internal resistance of the cell and find an accurate value for emf..
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actually the main thing tht works behind this galvanometer giving zero is the kirchoff's law itself.
when u consider the loop below, the potential difference on the wire above has a positive value while the emf (at B in this case) has a negative value, so that when u sum it up u get a resultant potential difference.
so to make the galvanometer give a zero reading, the potential difference on the wire MUST be equal to the emf( at B in this case).
thus if u are able to find the pd across the respective length of wire which gave a zero reading, then u actually found the emf of B!!!! :)
 
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Agassi Cazaubon

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nahid842 said:
actually the main thing tht works behind this galvanometer giving zero is the kirchoff's law itself.
when u consider the loop below, the potential difference on the wire above has a positive value while the emf (at B in this case) has a negative value, so that when u sum it up u get a resultant potential difference.
so to make the galvanometer give a zero reading, the potential difference on the wire MUST be equal to the emf( at B in this case).
thus if u are able to find the pd across the respective length of wire which gave a zero reading, then u actually found the emf of B!!!! :)
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Yea I know.. that is the principle I applied.. but I got 1.8V as the Pd 0.9/1 x 2v but you might be right because my method does not account for the other resistors
 
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nahid842

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i got E=1.3v
the current I= 0.289A :)
dont even think about it, they just give 1 MARK for the correct answer, all the marks u will gain is from the steps u have given. :D
so CHILLLLLLLLL!!!!!!!
A-levels almost OVER!!!!!
 
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xxxtoughxxx

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arlery said:
I think it was 0.2 A, but I don't remember for sure..
Emf was 2 V.
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but if it was to 2V like cell A the balance point would have been at the end of the junction i had it 1.8 V....anyway i dun thimk 4 marks matter that much (y)
 
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Agassi Cazaubon

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Guys I'm sure the emf was 1.03V even though I put 1.8V.. you couldn't have used the equation of the ratio of lengths multiplied by emf of battery because it assumed there are no other sources of resistance besides the wire.

You would I guess use the R(across length of 0.9m)/(total resistance) and you'd get 1.03V ... I think it was meant to be tricky like that..

So im guessing we'd get no marks at all for using the equation with the ratios either because we missed the point of the question :( so 3 marks lol.. no biggie
 
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1357913579

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Agassi Cazaubon said:
Guys I'm sure the emf was 1.03V even though I put 1.8V.. you couldn't have used the equation of the ratio of lengths multiplied by emf of battery because it assumed there are no other sources of resistance besides the wire.

You would I guess use the R(across length of 0.9m)/(total resistance) and you'd get 1.03V ... I think it was meant to be tricky like that..

So im guessing we'd get no marks at all for using the equation with the ratios either because we missed the point of the question :( so 3 marks lol.. no biggie
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thats what i did ALHAMDULILAH,
 
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1357913579

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ga7sh said:
was it elastic or inelastic?
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obviously inelastic as ke not conserved even you can write speed of seperation is not equal to speed of approach i remebr one was less and one was more so i wrote speed of aproach or seperation dont remeber but which one of these was more was more than speed of seperation or approach dont remebr which one of these but which was less.
 
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beauty princess said:
can anyone plz tell me what was the first part of circuits question in the paper..
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soory i dont remeber but i suppose theres no need to discuss now most of the people here would have forgot the answes.
though i rember that was easy to do it:)
 
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