A2 Physics | Post your doubts here

[namename]

A) = I e^-ux = I e^-(0.24)(0.4) = 0.9I

B) I (transmitted) = I (incident) - I (reflected)
I (transmitted) = 0.9I - ((Z2 - Z1) ^2 )/(Z2+Z1) ^2)) I
I (transmitted) = 0.9I - ((1.6-1.4) ^2)/(1.6+1.4) ^2)) I
So, I (transmitted) = 0.9I - (1/225) I = 0.896 I
Which is again, almost equal to 0.9I

C) = (0.896)I e^-ux = I e^-(0.23)(4.35) = 0.37 (0.896)I = 0.33I

D) I (transmitted) = I (incident) - I (reflected)
I (transmitted) = 0.33I - ((Z2 - Z1) ^2 )/(Z2+Z1) ^2)) I
I (transmitted) = 0.33I - ((6.5-1.6) ^2)/(6.5+1.6) ^2)) I
So, I (transmitted) = 0.33I - 0.37 I = -0.04I
Which is almost equal to 0 I.

Maybe the significant digits aren't exactly equal, but the process should be correct

That is exactly how i tried to approach this question... the answers are:
0.908I,
0.904I
0.332I
0.121I

I don't get how to get the last answer

 

[Idris]

SUUGEST WHY ULTRASOUND CANT BE USED TO EXAMINE BONES
ultrasound isn't used to image bones. you get plenty of reflection of the ultrasound energy at the tissue/bone interface, but very little transmission into the bone. That means there's little to no sound energy reflecting back from any boundaries within the bone for the transducer to detect. WELL ONE confusion we can i guess get the image of outline of bone isnt it cos we will be recieving the reflection from bone/.....it is only reflection from the other side of bone we ll not get ......so why we dont use it o examine deformities in bone

I am not sure though but to examine deformities within the bones we must have the transmitted wave, the reflected wave will just outline the structure, will not give us any information of the structure, for that you need a transmitted wave I hope you get it.

 

[SkyPilotage]

yes we should learn that how to calculate the bandwidth of op-amp and how to determine the frequency of FM, and signal frequencies.
I have tries to find a way to make u guys understand that how to calculate it bt am unable as itx only possible by any video link, which I donot have or by face to face to face convers. which is also.... a little difficult I gues.

there may be some one else who could try to make U understand abt it but m unable.....

please mention the syllabus point which states, learning bandwidth of op-amp.

 

[optimistic]

Hey please tell me when do we use V R.M.S and when do we use V0. I am confused in the question MAY/JUNE 2010 Q6b!
http://www.xtremepapers.com/papers/...nd AS Level/Physics (9702)/9702_s10_qp_41.pdf

 

[hassam]

please mention the syllabus point which states, learning bandwidth of op-amp.

well as for bandwidth....we only need to knw its meaning....i.e rangew of frequencies that are amplified by the sam amount....or over which gain is constant

 

[hassam]

Yes, you need to!

well no need to knw the derivcation of eq...1/3 *density*c^2

 

[namename]

ΔU = q + w.

Hey guys, from the 1st law of thermodynamics, If ΔU is negative, is that DECREASE in internal energy?

 

[SkyPilotage]

ΔU = q + w.

Hey guys, from the 1st law of thermodynamics, If ΔU is negative, is that DECREASE in internal energy?

yes, because delta u is the increase in internal energy.
Negative increase is a decrease!

 

[Idris]

helpful
Two consecutive peaks in an ultrasound A-scan
are separated by a time interval of 0.034 ms.
Calculate the distance between the two
reflecting surfaces. (Assume that the speed of
sound in the tissue between the two surfaces
is 1540ms-I.)
Explain why ultrasound cannot readily be used
to examine the brain. Suggest an alterrıative
scanning techniquels) that can be used for this
i have a very strong feeling that such a question will cum this tym

.The ultrasound wave cannot pass through bones,They are thus of limited use for examining regions that are surrounded by bone (such as the adult brain)

 

[hassam]

but why have they taken 40 days as half life?

well u completely mis unnnderstood it....volume=nRT/P
we knw every thing bt not n.......so we know how man alpha particles given out per second.....so we cn calculate how many given out in 40 days.......and since every alpha particle becomes helium atom....use this number....divide it by avogadro to get # of moles and BINGoo

 

[namename]

For the question why specific latent heat of vaporization greater than that of fusion
it is because there is greater increase in separation as well as the volume leading to ΔU more positive and w more negative. and so Q must be greater. correct?

ΔU = q + w.

 

[angelicsuccubus]

do I need to know how a nuclear reactor works?

 

[angelicsuccubus]

well no need to knw the derivcation of eq...1/3 *density*c^2

thank you

 

[namename]

Can you try to solve this?
Am I only the one the ms is weird?'

A.C current w/ equation I=9.9sin(380t)

 

[prannoy]

why does capacitor store only energy but no charge???

 

[hassam]

why does capacitor store only energy but no charge???

no charge stored capaciotor plates store equal charge of opposite signs so no overall charge.............and energy is stored since there is a charge separation.....to separate charges like this work must have been done

 

[prannoy]

Can you try to solve this?
Am I only the one the ms is weird?'

A.C current w/ equation I=9.9sin(380t)
View attachment 9350

p=I^2oR 400=9.9^2 R R=4.08

 

[hassam]

Can you try to solve this?
Am I only the one the ms is weird?'

A.C current w/ equation I=9.9sin(380t)
View attachment 9350

wenever u see mean power use rms value

 

[miss irfan]

can somebody please explain why have we divided the kinetic energy by 2 in Q2ii of November 2010 paper 43? we are required to calculate the temperature of the sample which contain both deteruim and protons and total kinetic energy is given then why dividing it by 2?

 

[optimistic]

well u completely mis unnnderstood it....volume=nRT/P
we knw every thing bt not n.......so we know how man alpha particles given out per second.....so we cn calculate how many given out in 40 days.......and since every alpha particle becomes helium atom....use this number....divide it by avogadro to get # of moles and BINGoo

My question still remains. Why is the rate of emission of Alpha particles assumed to be constant?