wave particle duality

Question 1

Explain how images are formed in a TEM.

Answer 1

→ electrons in the middle are undeviated
→ electrons on the edge are deflected by magnetic fields
→ condenser lens deflects electrons into wide parallel beam incident uniformly on sample
→ objective lens forms image of sample
→ projector lens magnifies image onto fluorescent screen

Question 2

What is the wave theory of light?

Answer 2

all points on a wave front are sources of secondary wavelets

Question 3

What did the wave theory of light predict about photoelectric emission?

Answer 3

classical wave theory predicted that all wavelengths / colours / frequencies of light should cause electrons to be emitted

Question 4

Describe and explain how the resolution of the image would change if potential were increased.

Answer 4

→ increase of pd increases the speed/momentum of electrons
→ electron wavelength would be smaller
→ electrons would diffract less (when they pass
through the lenses)
→ image would show greater resolution

Question 5

Describe how an STM is used to obtain an image of a surface.

Answer 5

→ probe moves across the surface, the size of the gap will vary
→ gap increases, tunnelling current decreases
→ variation of current with time is used to map surface