Physics: Post your doubts here!

[Akshajistari]

View attachment 59839

Can someone explain to me how the 240 is the root mean square speed ? And why we have to multiply it by root of 2 ?

I think you meant root mean square voltage

Well, the formula is usually Vrms=Vo/square root of 2

When the voltage of an alternating current is given without any other detail, it is assumed to be the Vrms.
And since you are comparing to a value that is a peak voltage(9.0V) you have to convert the 240 to peak value too.
So Vo=Vrms*square root 2

Hope I helped.

 

[holoholo]

I think you meant root mean square voltage

Well, the formula is usually Vrms=Vo/square root of 2

When the voltage of an alternating current is given without any other detail, it is assumed to be the Vrms.
And since you are comparing to a value that is a peak voltage(9.0V) you have to convert the 240 to peak value too.
So Vo=Vrms*square root 2

Hope I helped.

Yes thank you
Can you please explain sampling frequency ?

 

[Mayarzawaydeh]

hey does anyone know on what bases do we get our candidate numbers? I mean where does the count start from ( if that makes sense hahah)

 

[Mayarzawaydeh]

Try at gcecuide

thanks!!

 

[Akshajistari]

Yes thank you
Can you please explain sampling frequency ?

Sampling frequency as in the one in Communications?

 

[The Sarcastic Retard]

Yes thank you
Can you please explain sampling frequency ?

http://www.fon.hum.uva.nl/praat/manual/sampling_frequency.html

 

[Mayarzawaydeh]

http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s09_qp_4.pdf
can someone help me out in question 12 part c?? please its urgent!
thanks in advance!

 

[Rizwan Javed]

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".

 

[Saad the Paki]

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?

 

[Saad the Paki]

For part (i) why will the phase difference between 0?
For part (iv) why will the graph be a horizontal line through the center?

 

[Uchiha-Sasuke]

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 )

 

[Uchiha-Sasuke]

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

 

[Uchiha-Sasuke]

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

 

[Saad the Paki]

Thank you very much

 

[Uchiha-Sasuke]

Thank you very much

No problem, I just logged in to Xtreme papers after such a long time lol..

 

[Mayarzawaydeh]

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

Thanks in advance!!

 

[Hamza Malik 123]

Guys need help

 

[Saad the Paki]

Guys need help

What board is this?

 

[Saad the Paki]

Answer is A.... any idea how?

 

[Saad the Paki]

see solution 760 at
http://physics-ref.blogspot.com/2015/05/physics-9702-doubts-help-page-153.html

Thanks that helped but I have one question, in a series combination the total extension is the sum of the individual extensions regardless of the order in which the springs are hung so A and C should give the same extension for small loads.....?