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Physics: Post your doubts here!

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could you tell me from where you downloaded the ebook
It's a strange website. I just typed : a levels physics 2ed at yun.baidu.com in the google's search bar. It was the 3rd or 4th suggestion. You can try this for other books too. Type any books name, and at the end type "at yun.baidu.com".
 
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In my book it says "A battery delivers max power to a circuit when the load resistance of the circuit is equal to the internal resistance of the battery" can someone explain why?
 
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Screenshot_2016-03-28-01-09-13-1.png
For part (i) why will the phase difference between 0?
For part (iv) why will the graph be a horizontal line through the center?
 
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In my book it says "A battery delivers max power to a circuit when the load resistance of the circuit is equal to the internal resistance of the battery" can someone explain why?
Well, power supplied by the battery to the external resistor is = I^2 R. where 'R' is the resistance of the external resistor and 'r' is the internal resistance of battery. Take for instance that the e.m.f of the battery is V.
Case 1) when R > r
Lets assume external resistance R = 2r
I= V/(r+2r)
= V/3r
Power = (V/3r)^2 * 2r
= (2V^2)/9r
Case 2) when R < r
Lets assume external resistance R = 0.5r
I= V/(r+0.5r)
= V/1.5r
Power = (V/1.5r)^2 * 0.5r
= (2V^2)/9r

Case 3) when R = r
I= V/(r+r)
= V/2r
Power = (V/2r)^2 * r
= (V^2/4r)
= (2V^2/8r) (numerator and denominator multiplied by 2)

Conclusion:
Case 3 power > Case 1 power
(2V^2/8r) > (2V^2)/9r

Case 3 power > Case 2 power
(2V^2/8r) > (2V^2)/9r

Hence from this we can see the product of I^2 R will only be maximum when R = r
This is no different than the mathematics rule that if we break the number 20 into two of it's components x , y (such that x + y = 20) then x*y will have maximum value only when they are equal. i.e 10*10 = 100 ( maximum ) :)
 
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View attachment 59892
For part (i) why will the phase difference between 0?
For part (iv) why will the graph be a horizontal line through the center?
For a stationary wave, points in the same segment are in phase, while points in adjacent segments are in anti-phase (180o). This is because, apart from nodes, the points of a stationary wave can only move upwards or downwards. Here, point X and Y will both move downwards since the position displayed is that where the points are at their maximum displacement
Phase difference = zero (rad)

In the time = period of vibration τ, the new position of the points of the stationary wave will be the same as displayed. [Consider the antinode between X and Y. In 1 period, the point would have to move downwards to the horizontal line, then downwards to the maximum amplitude. Then, the point moves upwards to horizontal line again and finally to upwards to its original position. So in a time = τ, a point travels a distance equal to 4 x amplitude.] So, for time = τ /2, the new position would be the reflection about the horizontal line. For time = 0.25τ = τ /4, the new position be at the horizontal line check the image I'm uploading
 
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For a stationary wave, points in the same segment are in phase, while points in adjacent segments are in anti-phase (180o). This is because, apart from nodes, the points of a stationary wave can only move upwards or downwards. Here, point X and Y will both move downwards since the position displayed is that where the points are at their maximum displacement
Phase difference = zero (rad)

In the time = period of vibration τ, the new position of the points of the stationary wave will be the same as displayed. [Consider the antinode between X and Y. In 1 period, the point would have to move downwards to the horizontal line, then downwards to the maximum amplitude. Then, the point moves upwards to horizontal line again and finally to upwards to its original position. So in a time = τ, a point travels a distance equal to 4 x amplitude.] So, for time = τ /2, the new position would be the reflection about the horizontal line. For time = 0.25τ = τ /4, the new position be at the horizontal line check the image I'm uploading
 

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hey!!
can someone please help me in this question?
the question says: a fixed mass of an ideal gas undergoes cycle PQRP of changes as shown in fig.1

b(I) state the change in the internal energy of the gas during one complete cycle PQRP
b(ii) calculate the work done on the gas during the change from P to Q
b(iii)some energy changes during the cycle PQRP are shown in fig.2.
complete fig.2. to show all of the energy changes
fixed-mass-ideal-gas-volume-pressure-cycle-nov2010p42q2.png

fixed-mass-ideal-gas-energy-changes-nov2010p42q2.png

Thanks in advance!!
 
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