Optics

Question 1

2 types of spectroscopy?

Answer 1

Refraction (snell’s laws apply)

Grating (dsin(theta)=n*wavelength)

Question 2

Snell’s law?

Answer 2

n=c/v

n2/n1=Sin(theta2))/(Sin(theta1))=v1/v2

Question 3

Types of detectors

Answer 3

Eye
Photographic plates
CCD’s - current (photon counters)

Question 4

Considerations of CCD’s

Answer 4

• Quantum efficiency -fraction of photons detected
• Transfer efficiency - fraction of photons transferred between pixels
• Dynamic range - strongest-weakest distinguishable features on image

Question 5

Lens formula?

Answer 5

1/f = 1/u +1/v

u - object distance (-u = virtual object)
v - image distance (-v = virtual image)

Question 6

Magnification equation

Answer 6

-v/u

H/h

Negative = inverted image

Question 7

Sensitivity of a telescope

Answer 7

Energy collected over an exposed time of t

E=FAt

Question 8

Smallest angle that can be resolved under perfect conditions?

Answer 8

Theta = wavelength/telescope diameter

Diffraction limit

Question 9

Atmospheric turbulence?

Answer 9

Air pockets at various temperatures cause refraction
r0 - size of pocket (5-30cm)
t0 - coherence time (1-00ms - time for pocket to move by its size)

Question 10

What are speckles and when do they occur?

Answer 10

• Observation shorter than coherence time
• Atmosphere acts as a series of lens’s creating multiple patterns
• longer exposers = merged speckles

Reduced resolution = wavelength / r0

Question 11

Types of telescopes at ground, mountain and space range

Answer 11

Ground - Radio
Mountain - Optical
Space - UV/X Ray

Question 12

Interferometry

Answer 12

Combing multiple telescopes to form a larger image

Sensitivity = NPiD^2

Resolution = wavelength/distance telescopes are spread

Question 13

Angle of deflection for a gravitational lens

Answer 13

=4GM/c^2*distance from mass

For small angles use Einstein radius equation (given in exam)