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Biology; Chemistry; Physics: Post your doubts here!

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by v=ir i get 68ohms
answer is 292. er says that most students forgot to subtract. subtract what?
I also got 68 ohms but the current given is for 1.7 V, the circuit is of 9 V.
They want us to calculate for the whole circuit, R=9/0.025 (current is same throughout).
Then subtract 68 ohms from this. I have no idea why. :p
 
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I think I've got it,
The LED has a potential difference of 1.7 V,
The e.m.f. is 9 V,
The resistor hence has a potential difference of 9-1.7=7.3 V,
Minimum Resistance = 7.3/0.025 = 292 ohms.
i dint have a logic for my ans but now i got it :p
 
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I think I've got it,
The LED has a potential difference of 1.7 V,
The e.m.f. is 9 V,
The resistor hence has a potential difference of 9-1.7=7.3 V,
Minimum Resistance = 7.3/0.025 = 292 ohms.

i can not believe how silly i m. i have no right to live in this planet any more :cry:
they gave p.d of lamp but i calculator R of resistor by p.d of lamp. much a silly mistake. my teacher would not even tell me answer but have murdered me.
 
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i can not believe how silly i m. i have no right to live in this planet any more :cry:
they gave p.d of lamp but i calculator R of resistor by p.d of lamp. much a silly mistake. my teacher would not even tell me answer but have murdered me.
The key again. I directly went to this part and did not even see the circuit diagram! READ QUESTIONS PROPERLY. Whoever said that was a genius.
 
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:cry: I NEVER get reversible equation...and then I stopped bothering because I didn't find any question on them. :p any important question regarding reversible reactions u have seen? and if u could please tell me what are the main points to be grasped in order to get hold of the topic :-/ and explain them a bit too :p like what is state of equilibrium n stuff :unsure: and how will this knowledge be tested in the exam...

there are some questions related to reversible reactions in MCQs and in paper 2 as well, another question is in oct/nov 2008 and Usama has explained almost everything i guess and you should also know that adding catalyst increases the rate of both, forward and backward reaction. And this knowledge can be tested in the questions of haber and contact processes
 
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