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Physics: Post your doubts here!

NamelessIguana

NamelessIguana

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ashcull14 said:
View attachment 45285
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The Answer is B. Current always travels the path with the smallest Resistence. So when the switch is closed all current will flow through that wire and not through the resistor, hence there is no P.D across there. Next, since the current flows through the empty wire, there is an overall drop in resistence hence the Current increases.
Now, plox 20th from http://papers.xtremepapers.com/CIE/...nd AS Level/Physics (9702)/9702_s13_qp_12.pdf
 
A

ashcull14

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whts
NamelessIguana said:
The Answer is B. Current always travels the path with the smallest Resistence. So when the switch is closed all current will flow through that wire and not through the resistor, hence there is no P.D across there. Next, since the current flows through the empty wire, there is an overall drop in resistence hence the Current increases.
Now, plox 20th from http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s13_qp_12.pdf
Click to expand...
the ans is it A?
 
ZaqZainab

ZaqZainab

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NamelessIguana said:
The Answer is B. Current always travels the path with the smallest Resistence. So when the switch is closed all current will flow through that wire and not through the resistor, hence there is no P.D across there. Next, since the current flows through the empty wire, there is an overall drop in resistence hence the Current increases.
Now, plox 20th from http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s13_qp_12.pdf
Click to expand...
20)
Take the leftmost column of liquid.

There is a rule in fluid-statics that "the pressure in a sample of liquid is the same at any vertical height, as long as the fluid at that height is part of the whole."

What that says is that in any single sample of liquid, the pressure at any height is the same. Here, it means that the pressure at the top of the leftmost column (connected to the bulb) is the same as the pressure in the next column on the right at the same depth/height. (Neat info here)

So, take the unbroken fluid column on the left. At the top of the leftmost tube (which exposes the fluid to the pressure of the bulb), the pressure at the surface is simply 16,000 Pascals, because that is the pressure in the bulb and is also the pressure with which the gas pushes on any section of the surface around it. The liquid forms part of this surface, so the pressure on the liquid is also 16,000 Pascals.

Now let's move to the next column on the right, where the liquid column is exposed to pressure P. Where it is exposed to pressure P, the surface faces a pressure of P Pascals. This is to be expected. However, as we descend down the liquid, the pressure increases by (ρgh) at a depth h, and continues decreasing with depth.

When we reach depth h1, we note that this level coincides with the vertical level of the fluid in the leftmost column. The pressure on the right side column is
P + ρgh1, while the pressure on the left hand column is 16,000 Pascals. Since these are equal, we can write

P + ρgh1 = 16,000.

Repeating that calculation on the right side, we get

P + ρgh2 = 8,000

Eliminating P,

16,000 - ρgh1 = 8,000 - ρgh2
13,600 * 9.8 * (h1-h2) = 8000
h1 - h2 = 0.06

So the difference is 0.06 meters = 6 centimeters. The only option that agrees is D.
by thought blocker
 
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