Problem Set 2

Problem Set 2 - PHYSICS 230 PROBLEM SET 2 1. UNITS...

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PHYSICS 230 – PROBLEM SET 2 1. UNITS Theoretical physicists often work in units where ¯ h = c = 1. What does this mean? From the equation x = ct we see that if c = 1 then [ length ] and [ time ] are the same units. From the equation E = ¯ we see that [ energy ] and [ time ] - 1 are the same units. Using similar relations show that all cgs units can be expressed relative to one basic unit. Often this is taken to be [energy], say electron Volts. Express the size of a typical room, say 10 meters, in eV. Show in this system that [ G N ] = [ mass ] - 2 , where G N is Newton’s gravitational constant. Express G N in GeV. This mass, m P is called the “Planck Mass.” Express the Planck Mass m P as 1 /l P where l P is a length, the Planck Length. Express l P in centimeters. This mass and this length are where we expect quantum gravity effects to become important. Compare this mass to the mass of a minimum size raindrop, taken to be of radius 500 microns. Express the characteristic energy
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This note was uploaded on 02/01/2011 for the course MATH 171 taught by Professor R during the Spring '09 term at Stanford.

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Problem Set 2 - PHYSICS 230 PROBLEM SET 2 1. UNITS...

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