19th NOV 2013 test - study group

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delsub
Posts: 98
Joined: Thu Jun 24, 2010 12:17 am

19th NOV 2013 test - study group

hi

anyone here taking the Pgre test this 19th of November - if so please stand up. We could discuss and study together

how important is Pgre score in selecting a candidate for a PhD program (I am already in my last semester of MS Physics)

is a score of 750 decent - how many questions do i have to get correct to obtain 750?

blighter
Posts: 256
Joined: Thu Jan 26, 2012 6:30 pm

Re: 19th NOV 2013 test - study group

delsub wrote:hi

anyone here taking the Pgre test this 19th of November - if so please stand up. We could discuss and study together

how important is Pgre score in selecting a candidate for a PhD program (I am already in my last semester of MS Physics)

is a score of 750 decent - how many questions do i have to get correct to obtain 750?

I think you mean 19th of October. There's no PGRE this year in November.

delsub
Posts: 98
Joined: Thu Jun 24, 2010 12:17 am

Re: 19th NOV 2013 test - study group

yes october. lol

delsub
Posts: 98
Joined: Thu Jun 24, 2010 12:17 am

Re: 19th NOV 2013 test - study group

hey can someone pls explain this problem to me -

http://grephysics.net/ans/8677/12

why isnt the answer = D ==> 1.9 khz

I used the following equation ----------->

F'= F (V+Vs)/(V+Vo)

Here V = velocity of sound
Vs = velocity of source, taken positive if it is moving in the direction of the sound (i.e from the S to the O)
Vo = Velocity of observer, taken positive if it is moving in the direction of the sound.

Is something wrong with the equation

MomSaysImSpecial
Posts: 14
Joined: Sun Sep 29, 2013 12:07 pm

Re: 19th NOV 2013 test - study group

delsub wrote:I used the following equation ----------->

F'= F (V+Vs)/(V+Vo)

Here V = velocity of sound
Vs = velocity of source, taken positive if it is moving in the direction of the sound (i.e from the S to the O)
Vo = Velocity of observer, taken positive if it is moving in the direction of the sound.

I think, the equation is

F' = F * [(V+Vo)/(V+Vs)]

http://en.wikipedia.org/wiki/Doppler_effect

delsub
Posts: 98
Joined: Thu Jun 24, 2010 12:17 am

Re: 19th NOV 2013 test - study group

here is another i dont get at all -

http://grephysics.net/ans/8677/44

since the collision is elastic the KE is preserved.

so 1/2 mv^2 = 1/2 MV^2

or V = v(m/M)^1/2

so why are they saying answer is A

delsub
Posts: 98
Joined: Thu Jun 24, 2010 12:17 am

Re: 19th NOV 2013 test - study group

MomSaysImSpecial wrote:
delsub wrote:I used the following equation ----------->

F'= F (V+Vs)/(V+Vo)

Here V = velocity of sound
Vs = velocity of source, taken positive if it is moving in the direction of the sound (i.e from the S to the O)
Vo = Velocity of observer, taken positive if it is moving in the direction of the sound.

I think, the equation is

F' = F * [(V+Vo)/(V+Vs)]

http://en.wikipedia.org/wiki/Doppler_effect

no their convention of whats positive and whats negative velocity is different.

In my convention, all velocities along the direction of the wave - i.e from S to O is positive and opposite it is -ve.

So when S moves towards the O, Vs adds to V upstairs - to give a greater F
When S moves away from 0 - i.e in the direction opposite to S-->O, the Vs subtracts from V upstairs, to give a lower F.

Similarly with O -

so why is my equation not working ??

MomSaysImSpecial
Posts: 14
Joined: Sun Sep 29, 2013 12:07 pm

Re: 19th NOV 2013 test - study group

delsub wrote:so why is my equation not working ??

Let's try to derive it together.

When the observer doesn't have any speed in the medium, he can receive the signals of the circular frequency:

Omega = 2pi* (c/lambda)

Here 'c' is the speed of sound waves and 'lambda' is the wavelength of the 'new' wave. If we take into account the velocity of the source in the medium, we can see that:

lambda = 2pi*(c-v)/Omega0

'Omega0' is the original frequency of the source.

'v' is the speed of source with respect to the medium. Positive when (O<----S, the received wavelength is shorter since source is 'chasing' the original signal) and negative when (O S----->, the received wavelength is longer). Thus, we have:

Omega = Omega0/(1 - v/c)

We can also consider the case when the observer is moving and then get the general equation, but it is enough for our problem.

delsub
Posts: 98
Joined: Thu Jun 24, 2010 12:17 am

Re: 19th NOV 2013 test - study group

Thanks a lot. That solves it

I have another doubt or rather a set of doubts - i am getting confused every time i study it . can someone please help - with optics

What are the formula for MAXIMA in the following - I have filled up the ones I know (0= theta and L = lambda) - Please correct/complete

Slab of material ---------------------------------------------------> nt = (m+.5)n' L

Thin film interference-----------------------------------------------> 2nt = (m + .5) L

Young's Double slit Interference-------------------------------------> d sin 0 = (m+.5) L

Single slit Interference --------------------------------------------->

Diffraction Grating --------------------------------------------------> 2d Sin0 = m L

Bragg Diffraction

Raleigh Criteria/Aperture formula

delsub
Posts: 98
Joined: Thu Jun 24, 2010 12:17 am

Re: 19th NOV 2013 test - study group

Photoelectric effect Photon knocks out e-1. In Compton effect e-1 knocks out the photon
Stern Gerlach experiment Spin gerlach exp  Neutral atoms  2S + 1 due to spin
Frank Hertz experiment Electrons can be scattered elastically and Energy lost is discrete
Stark effect
Zeeman effect
Anomalous Zeeman effect
Hall effect To find positive or negative charge
Michelson Morley exp
Michael’s interferometer
Bohr postulate
Fine structure Spin orbit coupling
Lamb shift
Born Oppenheimer approx WF molecule = WF nucleus X WF electron
Born approximation In perturbation theory
Born assumption Psi square psi = probability
Fermi’s golden rule Perturbation – prob of transition from one Eigen state to a band of Eigen
Pauli’s exclusion principle Anti symmetric wave function
Pair production Particle and anti particle production
Auger transition Particle knocks inner electron out. Outer e-1 fills in + release of energy
Internal conversion An orbital electron is absorbed by nucleus and ejected along with an X-ray.
Gamma Ray Production The excited nucleus jumps to a lower level and emits a photon .
Photoelectric effect
Compton effect
Band spectra
Lamour precession
Lamour formula
Bremsterlung
Auger transition Particle knocks inner electron out. Outer e-1 fills in + release of energy
Cyclotron motion
Lamb shift
Fourier’s law
Malus law
Meyer’s eq
Brewster’s law
Brewster’s angle
Delong Petit law
Critical isotherm
Liquid vapor region

bosemicrowave
Posts: 27
Joined: Mon Jul 29, 2013 4:33 pm

Re: 19th NOV 2013 test - study group

Tomorrow exam.Best of luck for everyone.

There's a song(with no melody although) on you tube based on PGRE-Robert Lee,Steve Sigda(Oct8,2010).Now our time has come.

Song based on Wonder wall of OASIS.

delsub
Posts: 98
Joined: Thu Jun 24, 2010 12:17 am

Re: 19th NOV 2013 test - study group

yes gfood luck to everyone

meanwhile can someone explain what is happening in the following sums -

2001 - 84
1996-41 and
1986-84

http://grephysics.net/ans/8677/84