3.4. Wave optics, dual nature of light

Question 1

What is oscilation?

Answer 1

Repetitive variation in time of some measure about a point of equilibrium

Question 2

Huygens Fresnel principle

Answer 2

Every point on a wavefront is a source of wavelets. The new wavefront is a line tangent to all of the wavelets.

Question 3

What is the wavefront?

Answer 3

Set of all points where the wave has the same phase as the sinusoid

Question 4

What is an optical grating?

Answer 4

a large number of parallel, closely spaced slits that separate light of different wavelengths

Question 5

What is unpolarized light?

Answer 5

Light beam whose electric field vector can be found in any plane that contains the direction of propagation

Question 6

What is circularly polarized light?

Answer 6

Light beam which has a constant amplitude and its tip follows a helical path. Composed of 2 vectors shifted 1/4wavelength

Question 7

What is a phase contrast microscope?

Answer 7

optical microscopy technique that converts phase shifts in light passing through a specimen into brightness changes of the image

Question 8

What is the basic working principle of PC microscope?

Answer 8

separate the illuminating (background) light from the specimen-scattered light and to manipulate them differently

Question 9

What is the role of the phase shift ring?

Answer 9

phase-shifts background light by -90° to eliminate phase difference between background and scattered light. It also dims the background light

Question 10

What is the usual phase shift of light that has been through the specimen (in biological samples)?

Answer 10

-90° (because of density of specimen etc)

Question 11

What are the 6 important parts of PCM?

Answer 11

1. Light source
2. Condenser and annular aperture
3. Specimen
4. Objective
5. 90° phase shift ring
6. Image plane

Question 12

What is a polarization microscope?

Answer 12

A microscope that is used to observe specimens that are visible primarily because of their anisotropic character

Question 13

What is anisotropy?

Answer 13

for light, it is birefringence : n depends on the direction of polarization of light

Question 14

What does the energy of a wave depend on?

Answer 14

Only on its amplitude and not on its frequency

Question 15

Wavelength order of electromagnetic spectrum

Answer 15

Radio : 10^3 (m)
Microwave : 10^-2
Infrared : 10^-5
Visible : 10^-7
Ultraviolet : 10^-8
X-ray : 10^-10
Gamma ray : 10^-12

Question 16

What is 1eV?

Answer 16

Amount of kinetic energy gained or lost by a single electron accelerating through an electric potential difference of 1V in a vacuum

Question 17

What is the concept of a matter wave?

Answer 17

• All matter can exhibit wave-like properties

- For exemple electrons

Question 18

What is momentum?

Answer 18

quantity of movement

Question 19

What is resolution?

Answer 19

smallest distance between 2 points that can be observed

Question 20

What is the limiting angle of view?

Answer 20

smallest angle under which the eye can discern two points

Question 21

What is the electron gun?

Answer 21

Cathode emitting electrons, accelerated by an anode

Question 22

What are the electromagnetic lenses for?

Answer 22

coils that surround the tube that make an electromagnetic field to keep the electrons in the center and enhance image

Question 23

What is the acceleration voltage of the electron microscope?

Answer 23

between 50kV and 150kV

Question 24

What changes the power of resolution?

Answer 24

The acceleration voltage. The higher the voltage, the shorter the electron waves and the higher the resolution.

Question 25

What is the resolution of electron microscope?

Answer 25

d = 0.1 nm : 1000m the resolution of the light microscope

Question 26

What is the difference bewteen transmission and scanning electron microscope?

Answer 26

Transmission forms an image based on transmitted electrons, and scanning based on scattered electrons