Chapter 27 Early Quantum Theory & Models Of The Atom

Question 0

Darkrooms for developing black and white film are sometimes lit by a red bulb. Why red? Would such a bulb work in a darkroom for developing color photographs?

Answer 0

Red light have low frequencies, not enough energy emitted to create a reaction through photoelectric effect. Black/ white films change shape by other light (greater than the threshold). Color films are sensitive to red film because it has a lower threshold. Red light would turn the films all red; they need complete darkness.

Question 1

If energy is radiated by all objects, why can’t we see them in the dark?

Answer 1

Humans can only see the a small portion of the light spectrum. Ex. we can’t see gamma rays.

Question 2

If the threshold wavelength in the photoelectric effect increases when the emitting metal is changed to a different metal, what can you say about the work functions of the two metals?

Answer 2

One of the metal requires less work.
h • c / lamda = w
1 / lamda oc w
Increase wavelength, decrease work

Question 3

Explain why the existence of a cutoff frequency in the photoelectric effect more strongly favors a particle theory rather than a wave theory of light.

Answer 3

Intensity of light doesn’t matter, only frequency.
Wave theory = increasing intensity, more photons, more energy
Particle theory = energy of photon depends on the frequency
No individual photon has enough energy to ionize the atom.

Question 4

UV light causes sunburn, whereas visible light does not. Explain.

Answer 4

High frequency, more energy emitted by each photon, waves penetrate the skin more easily. Photoelectric effect is more likely to occur, when the atom is knocked off, the cell denatures.
E = h • c / lamda
Decrease wavelength, higher energy

Question 5

If an X-Ray photon is scattered by an electron, does its wavelength change? If so, does it increase or decrease?

Answer 5

h (before) = KE + W + h (after) 
h (before) is greater than h (after)  
The photon gives some of its energy to the electron during the collision.
E decreases, wavelength increases 
E = h • c / lamda
E oc 1 / lamda

Question 6

In both the photoelectric effect and in the Compton effect we have a photon colliding with an electron to fly off. What then, is the difference between the two processes?

Answer 6

In Compton scattering, energy is left over and requires a greater incoming energy photon.

Question 7

Why do we say that light has wave properties? Why do we say that light has particle properties?

Answer 7

Compton scattering, photoelectric effect, & para production is evidence of a particle (Photons knocking off electrons). Double slit experiment and thin films show wave properties (constructive and destructive).

Question 8

Why do we say that electrons have wave properties? Why do you say that electrons have particle properties?

Answer 8

Broglie proved that h / m • v = lamda
Anything with mass and velocity has a wavelength.
Electrons have particle properties b/c they have a mass of 9.11 E -31kg

Question 9

What is the difference between a photon an electron? Be specific: make a list.

Answer 9

Photon:                    
• energy packets      
• E = h • c / lamda.  
Electron: 
• can be transferred to other orbitals to create energy
• mass 
• E = q • V

Question 10

How can the spectrum of hydrogen contain so many lines when hydrogen contains only one electron?

Answer 10

The electron can be excited onto different orbitals/ have many phantom levels and different possible positions.