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Physics: Post your doubts here!

Duanoor

Duanoor

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Sound propagates by transferring energy from one particle of the medium to the other.
So when the medium particles will be close to each other (i.e. density of the medium is increased) the energy transfer will be faster and speed of sound will increase (this we see as speed of sound is zero in vacuum, having no energy carriers).
This implies that speed of sound must be proportional to density of the medium.

But in the expression v=sqrt (gP/r) speed of sound ‘v’ is inversely proportional to the density ‘r’ of the medium, and directly proportional to ‘g’(gamma) and pressure ‘P’.

Please explain.​
 
D

darknessinme

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farhan143 said:
My doubts in the following questions
can u please explain it to me...
View attachment 4548
Click to expand...

Q13 Think about which way the lever would turn with the forces. 5N and 10N turns the lever anti clockwise and 20N turns it clockwise.
Total moments= a.c.w moments + c.w moments. They are in opposite directions, so signs are different.
Total moments=(5Nx2m + 10Nx2m)+-(20Nx3m)=-30Nm. A is answer.

Q16 Power is rate at which work is done. The gradient will give this. Basically the question is asking when gradient(power) is maximum. This is during the period of 2-3s so the gradient from that is 30W, so answer is C.

Q34 Just note that resistance is the ratio of Voltage to current, so Voltage/Current at any point on the graphs give R. This has nothing to do with gradients or 1/gradients which is common misconception.
Now, you should know IV graphs for components in A. This is wrong. The resistance of Q is in fact decreasing so B is wrong. At 1.5A the resistances are almost the same so C is incorrect.
At 0.5A resistance for P=4ohm and Q=8ohm. Since P=V^2/R, the Power in P=2^2/4=1W and Power in Q=4^2/8=2W so infact D is correct.
 
farhan143

farhan143

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thnk you soo much
i've been waiting the whole afternoon and evening for the reply to my doubts
cuz i've this test 2mrw so im kinda preparin on past papers so
thanks again
hope more of my doubts will get cleared in this thread!
:):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):) :):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):):)
 
rz123

rz123

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KurayamiKimmi said:
http://www.xtremepapers.com/CIE/International A And AS Level/9702 - Physics/9702_s03_qp_1.pdf
ermm... q27 can anybody explain it ?
Click to expand...
c, the light from the lamp is not coherent. Coherent sources are those sources of light which emit continuous light waves of same wavelength , same frequency and are in same phase or have constant phase difference.
For observing interference phenomenon coherence of light waves is a must.
For light waves emitted by two sources of light , to remain coherent the initial phase difference between waves should remain constant in time. If the phase difference changes continuously or randomly with time then the sources are incoherent. Two independent sources of light are not coherent and hence can not produce interference because light beam is emitted by millions of atoms radiating independently so the phase difference between waves from such sources fluctuates randomly many times per second.
 
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