Hi Everyone,

    I have sort of let this thread languish, and for that I apologize.  With GRE exams coming up in the fall, I expect a fair number of you will be studying over the summer.  To assist you, I will be posting weekly practice questions for discussion.  Here's the first one:

Consider the quasi-static adiabatic expansion of an ideal gas from an initial state I to a final state F.  Which of the following statements is NOT true?

A. No heat flows into or out of the gas.

B. The entropy of state I equals the entropy of state F.

C. The change in the internal energy of the gas is the negative integral of PdV

D. The mechanical work done by the gas is the integral of PdV.

E. The temperature of the gas remains constant.

Post your answers, with justification, here.

Dave

Try not to become a man of success, but rather try to become a man of value -- Albert Einstein

To All Who are Taking the Physics GRE on Saturday:

Remember to stay calm, use your brain, and most importantly, DON'T PANIC!

Best of luck.

Dave

Try not to become a man of success, but rather try to become a man of value -- Albert Einstein

Hi Everyone,

     Sorry I am a little late getting this posted.  Gary's response to last week's question was correct.  His observation regarding GRE questions was also generally true.  Many GRE questions can be answered without doing a lot of calculations.  Here's this week's question.

Which of the following functions could represent the radial wave function for an electron in an atom?  (r is the distance of the electron from the nucleus, A and b are constants)

I. Aexp(-br)

II. Asin(br)

III. A/r

A. I only

B. II only

C. I and II only

D. I and III only

E. I, II, and III

Dave

Try not to become a man of success, but rather try to become a man of value -- Albert Einstein

Things got a little hectic last week, so I'm a little late with a new question.  Here it is:

A particle is constrained to move in a circle with a 10-meter radius.  At one instant, the particle's speed is 10 meters per second, and is increasing at 10 meters per second squared.  The angle between the particle's velocity and acceleration vectors is

A. 0 degrees

B. 30 degrees

C. 45 degrees

D. 60 degrees

E. 90 degrees

Have fun!

Dave

Try not to become a man of success, but rather try to become a man of value -- Albert Einstein

This one is really a definition, but here it is

In the production of X-rays, the term "bremsstrahlung" refers to which of the following:

A) The cut-off wavelength of the X-ray tube.

B) The discrete X-ray lines emitted when an electron in an outer orbit fills a vacancy in an inner orbit of the atoms in the target metal of the X-ray tube.

C) The discrete X-ray lines absorbed when an electron in an inner orbit fills a vacancy in an outer orbit of the atoms in the target metal of the X-ray tube.

D) The smooth, continuous X-ray spectra produced by high-energy blackbody radiation from the X-ray tube.

E) The smooth, continuous X-ray spectra produced by rapidly decelerating electrons in the target metal of the X-ray tube.

Dave

Try not to become a man of success, but rather try to become a man of value -- Albert Einstein

Hi Everyone,

     I just posted the answer to last week's question, so here is another one for you to think about.


Five positive charges of magnitude q are arranged symmetrically around the circumference of a circle of radius r.   What is the magnitude of the electric field at the center of the circle?  (k=(4*pi*epsilon0)^-1)

A. 0

B. k*q/r^2

C. 5*k*q/r^2

D. (k*q/r^2)*(cos(2*pi/5))

E. (5*k*q/r^2)*(cos(2*pi/5))

I will post the answer next week.

Dave

Try not to become a man of success, but rather try to become a man of value -- Albert Einstein

Hi Everyone,

     We are starting a new thread in which we will post and discuss questions from sample physics GRE exams.  The idea is that we will spend a week discussing approaches to answering the question, and hopefully at the end of the week have the correct answer.  Please post any discussion you have in this thread.

Here is this week's question:

The coefficient of static friction between a small coin and the surface of a turntable is 0.30.  The turntable rotates at 33.3 revolutions per minute.  What is the maximum distance from the center of the turntable at which the coin will not slide?

A. 0.024 m
B. 0.048 m
C. 0.121 m
D. 0.242 m
E. 0.484 m

Let the discussion commence.  If we get the answer to this question before next week, I will post another.

Dave

Try not to become a man of success, but rather try to become a man of value -- Albert Einstein