1.6 Using radiation to investigate stars Flashcards
What is a continuous spectrum?
Stars emit light as a continuous spectrum of radiation. This comes from the dense gas of the surface of the star.
Looks like a bar of rainbow.
What is a line absorption spectrum?
Light emitted from stars have to pass through gasses in the stars atmosphere. These gasses absorb certain wavelengths of light which leaves black lines on the continuous spectrum.
What is a black body?
A black body is a body (or surface) which absorbs all the electromagnetic radiation that falls upon it.
Stars are very good approximations to black bodies.
Although stars are obviously not black, they are almost perfect ‘emitters’ of electromagnetic radiation.
When we look at the light emitted by a star, we should get a continuous spectrum (all colours and wavelengths)
What does a black body spectrum look like?
Intensity up the side and wavelength on the bottom. Multiple curves with different temperatures.
-the higher the temperature, the higher the peak intensity
-the higher the temperature, the lower is the peak intensity wavelength, i.e. the peak is shifted to the left at higher temperatures
-the lower the temperature, the longer the ‘flat’ section is before the curve ‘lifts off’.
What is Wiens displacement law?
Wien’s law states that the wavelength of peak emission from a black body is inversely proportional to the absolute (kelvin) temperature of the body:
peak max=W/T
peak max = wavelength of peak emission (m)
T = absolute temperature (K)
W = Wien constant = 2.90×10 −3 mK.
What is Stefan’s law?
he total electromagnetic radiation energy emitted per unit time by a black body is given by
P=AσT ^4
P = power (W)
A = surface area of the black body (m2)
T = absolute temperature (K)
σ = Stefan constant = 5.67×10-8
What is the luminosity of a star?
-The luminosity of a star is the total energy it emits per unit time in the form of electromagnetic radiation.
-The unit of luminosity is the watt, W.
-Therefore, luminosity is equivalent to the power of the star.
What is intensity?
Less energy strikes each square metre of a surface per second as the distance from a light source increases.
This is because the light initially emitted is spread out over a larger and larger ‘surface area’ as it travels away from the source.
The ‘amount of light energy striking each metre square per second’ is known as the intensity, I
What is the inverse square law?
Inverse square law states that the intensity of radiation from a star is inversely proportional to the distance from the star squared.
I= P/4πR^2
I = intensity of the radiation (Wm −2)
P = total power (luminosity) produced by the star (W)
R = distance from the star (m).
