practice quick questions at end of sectionsowocki/phys333/lec03-18feb.pdf · lec03-18feb author:...
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Assignments for Thurs. 20 Feb
• Review secs. 1-5 of DocOnotes– practice Quick Questions at end of sections
• Do HW1 – due 5 p.m. Thursday• submit to my office 205 Sharp Lab• or my mailbox in 217 Sharp Lab
1
A. 10
B. 5
C. 1
D. 0
E. -52
Star 1 has an apparent brightness that is 100 times that of Star 2. What is the difference in their apparent magnitude m2-m1
Stellar magnitudes
3
Apparent magnitude:
A. 10
B. 5
C. 1
D. 0
E. -54
Two stars have the same Luminosity but star 2 is 10 times further away than star 1. What is their apparent magnitude difference m2-m1?
Stellar magnitudes
5
Apparent magnitude:
The relationship between apparent brightness (a.k.a. “flux”) and luminosity depends on distance:
Luminosity Flux = 4π (distance)2
We can determine a star’s luminosity if we can measure its distance and apparent brightness:
Luminosity = 4π(distance)2 ✕ (flux)
L = 4πd2F
F = L4πd2
A. 10
B. 5
C. 1
D. 0
E. -57
Two stars at the same distance have a luminosity ratio L2/L1= 100. What is their apparent magnitude difference m2-m1?
A. 10
B. 5
C. 1
D. 0
E. -58
Two stars have a luminosity ratio L2/L1= 100. What is their absolute magnitude difference, M2-M1?
Stellar magnitudes
9
Apparent magnitude:
Absolute magnitude:
Distance modulus:
Surface Brightness
10
11
Light• c = λν– speed = wavelength frequency
• E = hν– Photon energy = Planck constant x frequency
12
A. 1
B. 2
C. 1/2
D. 1/4
E. It depends on the amplitude of the associated light.13
Two photons have a wavelength ratio λ2/λ1= 2. What is energy ratio E2/E1?
Planck Blackbody function
14
Bυ =2hυ3 / c2
ehυ /kT −1Bλ =
2hc2 / λ5
ehc/λkT −1Bλdλ = Bυdυ
Peak wavelength
15
λ peak ; 500nmTeT
A. 500 nm
B. 250 nm
C. 1000 nm
D. 125 nm
E. It depends on the stellar radius.16
For a star with a surface temperature of 12,000 K, at about what wavelength λpeak does the spectrum have it peak flux?
Stefan-Boltzmann law
17!!
LL
⊙
=TT
⊙
⎛
⎝⎜
⎞
⎠⎟
4RR
⊙
⎛
⎝⎜
⎞
⎠⎟
2
Bλ dλ0
∞
∫ = Bυ dυ0
∞
∫ =σ sbT
4
πL
4πR2= F = πB =σ sbT
4
A. Lsun/4
B. Lsun/2
C. Lsun
A. 2 Lsun
B. 4 Lsun18
What is the luminosity of a star with a surface temperature of 12,000 K and a radius of Rsun/2?
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20
21
UBV Color Filters
22
23
A. 0.25 Rsun
B. 0.5 Rsun
C. 1 Rsun
A. 2.5 Rsun
B. 4 Rsun 24
What is the radius of a star with parallax 0.01arcsec, peak wavelength 250 nm, and apparent magnitude m=+5?
Assignments for Thurs. 20 Feb
• Review secs. 1-5 of DocOnotes– practice Quick Questions at end of sections
• Do HW1 – due 5 p.m. Thursday• submit to my office 205 Sharp Lab• or my mailbox in 217 Sharp Lab
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