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Physics Paper 61 (Varient 1 Paper) Electricity

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Chemguy

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Hey guys :D

So we had this sort of question about the parallel and series circuits, and in the part (a) the question goes like:

Find the sum of the resistances you calculated (they were like 5.3 and 5.9 ohms, i dont remember)

I used the Combined resistance formula (R1*R2/R1+R2) to get the answer of 2.8 ohms.
A friend of mine went sarcastic and he said: "SUM doesnt mean TOTAL or COMBINED resistance". He added them up to get around 11 ohms and he thinks he's right :)

Any idea who of us deserves a blow on the head? :p
 
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Gunner1995

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You do. They didnt ask for the TOTAL resistance in the circuit. They just said "Add the R values and get Rt... Thats it, Nothing complicated. Wear a helmet :) Answer was 11.something
 
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Gunner1995

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But they didnt ask for the total resistance,,, Ouff just listen. WHEN FINDING THE TOTAL RESISTENCE. YES IT IS IN PARALLEL AND SO YOU USE THE FORMULAE. that wasnt the question, They said "Add together the R values you calcuted to get Rt" And just follow the question and get 11.
This is a core paper, You werent supposed to know any formulaes and everything was givin, its a test to see if you can follow instructions... I spent 10 minutes during the exam thinking about it..
 
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Gunner1995

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No we didnt x_X FACEPALMMM!!! The question didnt want us to find the total resistance in the WHOLE CIRCUIT. that wasnt the question.. It was for the other section.. It just first asked us to calculate the resistance of 2 lamps.. Then ADD.... R1+R2. NOT THE WHOLE CIRCUIT
 
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Chemguy

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Gunner, with all my respect here man, Rt is soooo meaningful! (reminds you of Rtotal?) :)

chill out there's no need to shout cuz it's over, whoever got it right or wrong, we have nothing to do but wait. im just discussing it :)
 
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Gunner1995

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Im sorry, i dont mean to shout. But it is rtotal.. But not the total of the circuit. Its the total of the 2 resistance, Why would the theory then state that resistance in parallel = resistance in series.. Thats BS.
What me and all my friends have agreed on. Is that, The experiment asked us to find resistance of bulb one. 5. something
then of bulb two. 5. something. The theory was that these two added together, normal adding would equal when they are in series and that was when the theory was proven wrong, If you did the formulae ud get 2. something. Which is wayy off the 8 . something for the other resistance in series, Just think of it experimentely... My teacher always said, Dont be a genius with these papers, Its core, Just follow what they tell you. If they say add then ADD. Dont try using a formulae. Unless they gave it to you...
 
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Gunner1995

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Its over now, ,We need to focus on the other papers, its 1 mark. We dont know for sure the right answer, Im just giving my opinion..
Because in the exam room i said. Should i use the formulae. But no formulae was givin, THEY had to give you a formulae if they wanted the total resistance IN THE CIRCUIT. They even gave us R=V/I
 
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Chemguy

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Ok lets recall the whole question and ill just jot down the answers straight away.

Please calm down and try to see it from where I stand :)

(a) *parallel circuit is shown* Find sum of resistances.
combined resistance formula gets Rt= 2.8 ohms. ill tell u why i believe im right

(b) *series circuit shown, and values of 1.9V and 0.23A are given* Calculate total resistance:
Rs=V/I =1.9/0.23 = 8.3 ohms.

The next question is the tricky part:

(c) the student thinks that Rs and Rt are equal. Justify from calculate values and write ur statement.
(ok were finally here. how can u possibly compare a SUM (Rs+ Rt) with a TOTAL RESISTANCE? Seriously you cant compare 32 degrees F with 0 degrees C and say that F is higher JUST because F is numerically higher in value. The values MUST resemble the same aspect; I cant say im fat because im 190cm tall and ur 60kgs !)

BOTH must be total resistances :D :p
 
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Gunner1995

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Ok you have a point. But what the student was finding, which we did a similar experiment in class. IS , have a parallel circuit. Then find resitance of one bulb, then find the resistance of the other, They should be similar. And once You put these two bulbs in a series circuit. Then the question says. Rs = Rt. which means... Is the value of the two bulbs ADDED together in series the same as each seperate resistance added together in parallel
Anyways, Its 1 mark, And it was tricky. And none of us are for sure, We dont have the mark scheme :) We'll see when the mark scheme comes out
Cheers :)
And sorry for my attitude if i shouted or anything
Really sorry
 
WayneRooney10

WayneRooney10

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We just had to add em up. The answer was 11.x . Use common sense. The question was worth 1 mark. There is no way they would expect us to use that formula.
 
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cheesww

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Guys that formula for resistance in parallel shuldnt be used, my reasons are as follows:

1- In paper 6 they HAVE NEVER EVER expected you to use a formula without giving it to you! NEVER!

2-it said SUM! i dont know abt yu guys but where i come from sum means addition.

3- im not sure abt this one....but i think paper 6 is core....nd the formula for resistance n parallel isnt used in coe (thatz wht i was told)

Im not sure abt the 3rd point but im sure about the first 2 :D
 
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Walid05

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cheesww said:
Guys that formula for resistance in parallel shuldnt be used, my reasons are as follows:

1- In paper 6 they HAVE NEVER EVER expected you to use a formula without giving it to you! NEVER!

2-it said SUM! i dont know abt yu guys but where i come from sum means addition.

3- im not sure abt this one....but i think paper 6 is core....nd the formula for resistance n parallel isnt used in coe (thatz wht i was told)

Im not sure abt the 3rd point but im sure about the first 2 :D
Click to expand...

+1 :good:

، ،

If they want you to use any formulaes they should give it to you like the v=ir and the refractive index :)
but in the question he just said add so he means add both r

and paper 6 is a core paper + they never test how many rules you studied , in paper 6 they always give u the instructions and you follow then u say whether the theory is right or wrong
 
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Chemguy

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u know what, im convinced :p

not being sarcastic here, but i over-estimated shit x.x"

who's got the baseball bat? :p
 
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seemo1995

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Chemguy said:
Ok lets recall the whole question and ill just jot down the answers straight away.

Please calm down and try to see it from where I stand :)

(a) *parallel circuit is shown* Find sum of resistances.
combined resistance formula gets Rt= 2.8 ohms. ill tell u why i believe im right

(b) *series circuit shown, and values of 1.9V and 0.23A are given* Calculate total resistance:
Rs=V/I =1.9/0.23 = 8.3 ohms.

The next question is the tricky part:

(c) the student thinks that Rs and Rt are equal. Justify from calculate values and write ur statement.
(ok were finally here. how can u possibly compare a SUM (Rs+ Rt) with a TOTAL RESISTANCE? Seriously you cant compare 32 degrees F with 0 degrees C and say that F is higher JUST because F is numerically higher in value. The values MUST resemble the same aspect; I cant say im fat because im 190cm tall and ur 60kgs !)

BOTH must be total resistances :D :p
Click to expand...
im sorry to tell u that u've done part one wrong cuz the answer is 11.3 as i remember
cuz the question simply asked to find the sum
and if u r correct, then y didnt the examiner say combined electricity as he/she said when asking about the Rs (the one for series) ?
and also y didnt he write the formula since the formula of finding R was written alto its very obvious and known !!
it is 11.sth and not 2.sth !!!!!!
 
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cheesww

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AhmedNES said:
someone help how they drew the circut when it was in series
Click to expand...

itz basically the same..
the voltmeter was above the power supply inorder to measure the potental difference....
nd the 2 lamps n series! :D
 
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AhmedNES

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what about question 5 was the current in the 1.5V lamp 0.12A plz reply as soooooooooooooooon as possible :)
 
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Adahshan

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Gunner is right. It's total.

R1*R2/R1+21 won't work, It has to be done totally, both added.. 11. something and the other resistance was 8.26 or something.
 
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