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Modern Midterm 2
N/A
51
Physics
Undergraduate 1
11/14/2012

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Term
Schrodinger Equation
Definition

     d^(2)psi      -2m[E-U(x)]psi(x)

                     ---------- =    ---------------------              

                      dx^(2)              hbar^(2)

 

Term
de Brogile Wavelength 
Definition

it increases as the particle's kinetic energy decreases

 

Term
When is the de Brogile wavelength the same at all positions?
Definition
if U is constant then K is constant, thus the de Brogile wavelength is the same at all positions
Term
What is the relationship between the de Brogile wavelength with K
Definition
inverse relationship...as K increases the wavelength decreases
Term
When can you solve the Schrodinger equation?
Definition
It can't be solved until U(x) has been specified
Term
Boundary Conditions
Definition
The conditions or restrictions on acceptable solutions
Term

Primary Conditions a Wave Function must obey:

 

Definition

1. psi(x) is a continuous function

2. psi(x)=0 if x is in a region where it is physically impossible for the particle to be.

3. psi(x) --> 0 as x--> +infinity and x --> -infinity

4. psi(x) is a normalized function

Term
General Solution for psi(x)
Definition
psi(x)= Apis1(x) + Bpsi2(x)
Term
How to solve a quantum mechanics problem
Definition

1. Determine a pontential-energy function.

2. draw the potential energy curve

3. establish the boundary conditions that the wave function must satisfy.

4. normalize the wave functions

5.draw graphs of psi(x) and lpsi(x)l^(2)

6. determine the allowed energy levels

7. calculate probablities, wavelengths, or other quantities

Term
What are the solutions to the Schrodinger equation?
Definition
The stationary states of the system
Term
Jumping from one stationary state to another
Definition

      deltaE     lEf-Eil

                          f = ------- =  --------

                                  h            h

Term
What does a standing de Brogile wave lead to?
Definition
It leads to an energy quantization; only discrete energies allowed
Term
Rigid Box
Definition
a box whose walls are so strudy that they can confine a particle no matter how fast the particle moves.
Term
Characteristics of a Rigid Box
Definition

1. The can move freely between X=0 and X=L at a constant speed; constant K.

2. No matter how much K, the turning points are at 0 and L.

3. The regions x<0 and x>L are forbidden. The particle cannot leave the box.

 

Term
Potential Energy for a Rigid Box
Definition

U(x)= 0            0(</=) X (</=)

U(x)= infinity      X<0  or X>L

Term
Finding the Wavefunction
Definition

1. since U(x)=0 then the second derivative of psi in respect to x is   -2mEpis(x)

                                         =  ------------

                                              hbar^(2)

2. Beta^(2)   2mE

                = ------

                    hbar^(2)

Term

What functions second derivative is a negative constant times the function itself?

 

Definition

psi1(x)=sin(Betax)          psi2(x)=cos(Betax)

2. Then you take the second derivative of each psi and put it in the psi(x)=Apsi1(x) + Bpsi2(x)

 

Term
Why B=0?
Definition
For x=o psi(x)=o for this condition and the B part does not fit the property.
Term

Where X=L:

psi(x=L)=Asin(betaL)=0

Definition

1. solve for (beta)*(L); so find a constant that helps achieve sin(betaL)=0

2. solve for beta and plug it into psi(x)

Term
Solving for Energy
Definition

since Beta     sqrt(2mEn)    npi

               =   ---------  =  -----       n=1,2,3...

                      hbar           L

2. solve for energy En=n^(2) h^(2)/8mL^(2)=n^(2)E1.

 

Term
Energy En
Definition

1.these are the only values forE for which there are physically meanigful solutions to the Sch. equation.

2. it is the energy of the stationary state with quantum number n

3. E1 is the ground state energy

Term
Normalizing the equation
Definition

1. equation on reference sheet.

2. solve for An, which seems to always equal sqrt(2/L).

Term
Nodes and antinodes for psi(x)
Definition
has (n-1) nodes and n antinodes (maxima and minima).
Term
Zero-Point Motion
Definition

a quantum particle in a box cannot be at rest

E1 is the zero-point motion

Term
Condition for having a Stationary wave
Definition
the de Brogile waves have to form standing waves
Term
Correspondence Principle
Definition
Bohr's idea that the quantum world should blend smoothly into the the classical world for high quantum numbers. 
Term
What is the probability of finding a classical particle within a small interval dx
Definition

the fraction of its time that it spends passing through dx

Probclass(in dx at x)=(dt/.5T)= (2/Tv(x))

Term
Classical Probability density
Definition
Pclass(x)=1/L
Term
Finite Potential Wells
Definition

1. classically forbidden regions are E<U0

2. the wave function on the graph extends into the classically forbidden area

3. there are only a finite number of bound states

4. represent electrons confined to or bound in the potential well

5.no stationary states E>U0

Term
Finite Potential 2
Definition

1. because the wave functions are slightly more spread out, you get a lower velocity and thus lower energy.

 

Term
Classically Forbidden Region
Definition

1. e^(x/P.D.) and e^(-x/P.D.) are used where psi(x)=Ae^(x/P.D.) + Be^(-x/P.D.)   for x greater than or equal to L

2. psi-->0 as x-->infinity

3. since e^(x/P.D.) diverges as x--->infinity A=0

Term
Psi edge
Definition

psi(at x=L)= Be^(-L/P.D.)= Psiedge

1. solve for B to get Psi(x)=Psiedge e^-((x-L)/P.D.) for X (>/=)L

Term
Pentration Distance
Definition

P.D.          hbar

      =  ---------------

            sqrt(2m(U0-E))

Term
Quantum Harmonic Oscillator
Definition

w=sqrt(k/m)

U(x)=.5kx^(2)

Term
Quantum-Mechanical Tunneling
Definition

1. A higher total energy line means a larger K not a higer elevation

2. tunnels its way through the hill and emerges on the other side

3. requires not expenditure of energy

Term
Energy for Hydrogen ch.42
Definition

En= -13.60eV/n^(2)  n=1,2,3

n is the principal quantum number

Term
Angular Momentum
Definition

L= sqrt(l(l+1)) hbar  l=0,1,2,3..., n-1

l is the orbital quantum number

Term
Z-component of the angular momentum
Definition

Lz= (m)(hbar)   m=-l, -l +1,...,0,..., l-1, l

m is the magnetic quantum number

Term
Angular Momentum is Quantized
Definition

thetalm=cos^(-1)(Lz/L) 


ground state of l=0 has no angular momentum

Term
Ionization Energy
Definition
absolute value of E1=13.60eV, is the minimum energy that would be needed to form a hydrogen ion by removing the electron from the ground state.
Term
Otto Stern and Walter Gerlach
Definition

1. prepare an atomiv beam by evaporating atoms out of a hole in an oven

2. an atom whose magnetic moment vector mnu is tilted upward (mnu >0) has an upward force on it's north pole that is larger than the downward force on its south pole.

3. a downward tilted magnetic moment (mnu<0)experiences a net downward force 

4. A magenetic moment perpendicular to the field (mnu=0) feels no net force and passes through the magenet with no deflection.

Term
Spin Quantity Number
Definition

1. ms= (+/-)1/2

2. spin up state is the positive and spin down is the negative

3. The electron's spin is an intrinsic quantum property of the electron that has no classical counterpart

Term
Excitation :Absorption
Definition

delta l= absolute value of l2-l1=1


lamda= (hc)/(deltaEatom)

Term
The Decay Equation
Definition

Nexc=N0e^(-t/T)

where T=1/r

r is the decay rate =Prob(emission in deltat at time t)/(deltat)

Term
Laser 
Definition

Epulse=(Power)(deltat)

Ephoton= hf=(hc)/(lambda)

Epulse=N (Ephoton)

Term
Isotopes
Definition
  • the atoms of an element with different values of A; where A=Z+N
  • only 266 are stable
  • isobars- same A but different Z and N
Term
Nuclear Size and Density
Definition
  • r=r0A^(1/3) where r0=1.2fm
  • all nuclei have the same density of 2.3 x10^(17) kg/m^(3)

Term
Binding Energy
Definition
  • The energy you would need to supply to a nucleus to disassemble it into individual protons and neutrons
  • B=(ZmH +Nmn - matom) x(931.49)
  • peaks ingraph are due to closed shells
  • nuclear force is a short-ranged force
  • heavier nuclei can become more stable by breaking into smaller pieces
  • lighter nuclei can become more stable by fusing together
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