Karteikarten
Astrophysics
Karten in diesem Stapel (51)
- 1What kind of lens is in the eye and what effect does it have on rays?Convex, makes them converge
- 2What happens if uImage is formed on the same side as the object
- 3What Happens if u=f for a converging lens?No image is formed emerging rays are parallel to the principal axis
- 4In terms of focal length what happens to v as u increases?It decreases. f2f, u=2f v=2f, u>2f f
- 5What happens if u>f to the image formed?Inverted
- 6What happens if u>v to the image formed?Diminished
- 7What happens if u=v to the image formedsame size
- 8What happens if uMagnified image
- 9Describe the image formed by a camera and deduce u and v.Real, diminished and inverted. U>2f v
- 10Describe the image formed by a photocopier and deduce u and v?Real, same size and inverted. U=2f v=2f and v=+
- 11Describe the image formed by a projector and therefore deduce u and v?Real inverted and magnified. f2f v=+
- 12Describe the image formed by a magnifying glass and u and v?Virtual, upright and magnified u2f
- 13Describe The image formed by an object placed before a concave lensvirtual upright and diminished f
- 14Describe the image formed by an eyepiece lens of a refracting telescope set at normal adjustmentImage formed at infinity u=f v=infinity.
- 15What happens in chromatic aberration?blue light has a shorter wavelength and therefore refracts more than red light. Its principal focus is closer to the lens
- 16What is resolving power equal to?Minimum angular resolution that a telescope can achieve between two objects so that they can be resolved.
- 17Name three similarities between a radio telescope and an optical telescope?the objective dish and mirror are parabolic. Parallel rays are reflected to the primary focus where the detector/antenna is located. Source of the rays must be tracked or it will be lost from view as the Earth rotates.
- 18Name four strong radio sources?Jupiter the Milky Way the sun and unusually active galaxies.
- 19Why must radio telescopes be used to map the Milky Way?Dust clouds absorb visible light
- 20Name a similarity between infrared telescopes and radio telescopes?A huge concave reflector focuses infrared radiation onto an infrared detector at the focal point of the reflector.
- 21Name 3 non-visible sources of infrared radiationDying stars dust clouds and planets which aren't hot enough
- 22Name four sources of UV light?Hot gas clouds near stars, supernovae,quasars and hot, glowing comets.
- 23How do x-ray telescopes work?They reflect x-rays off highly polished metal plates at a grazing incidence on to a suitable detector.
- 24How do gamma telescopes work?Detects Gamma photons as they pass through a detector containing layers of pixels. The photons trigger a signal in each pixel they pass through. The signal can be used to determine the direction of incident photons.
- 25Why are Optical telescopes often situated high up in the atmosphere?to avoid atmospheric distortion; twinkling.
- 26Why are optical telescopes placed away from centres of population?To avoid light pollution.
- 27Why are radio telescopes placed away from centres of population?To aVoid sources of terrestrial interferences.
- 28What are the advantages of reflecting rather than refracting telescopes? (5)Can be made wider and hence produce brighter images (d^2 is directly proportional to light gathering abilities)and have better resolving powers. They do not experience chromatic aberration and spherical aberration is easily corrected. Larger mirrors are also more easily supported then lenses so less distortion occurs. There is little absorption of light so more light enters the eye. In addition to this a reflector the same size as a refractor will have a greater angular magnification than its counterpart.
- 29What are the advantages of refracting telescopes over reflecting? (3)Convex mirrors block light so less light hits the objective. Light is diffracted when passing through the secondary mirror which affects the image. A larger angular magnification means a smaller field of view. This makes it more difficult to locate an object.
- 30Name a use of a CCD and explain why it is suitable for taking fast changing astronomical images.Taking IR/UV/visible light images as it responds faster than film
- 31Define a parsecDistance to an object subtending one second of an arc to the mean radius of the Earth's orbit of the sun.
- 32What is the scale for apparent magnitude?-25 to +25
- 33Describe the black body curveHot objects emit radiation across a wide range of wavelengths. The peak intensity is at a given wavelength. The hotter the object object, the shorter the peak wavelength but the higher the peak (greater intensity). The area under the curve is equal to the intensity.
- 34Name four things to remember about the blackbody curve.intensity-wavelength axis, 12,000 K-300 nm, 6000 K-450nm, 4000K-800nm
- 35What Assumptions are made in deriving the inverse square law?Light travelling through interstellar space hasn't suffered any absorption. Pollution, dust, moisture and the Earth's atmosphere don't absorb the light. The total power output of the star is completely visible light.
- 36When does one of these assumptions become particularly obvious?When looking at very hot stars its peak wavelength is well into UV as they will appear very faint.
- 37how is this issue resolved?The intensity of the star above the Earth's atmosphere must be measured over all wavelength using a Balometer
- 38How are visible absorption line spectra caused?White light is shone through a gas. Photons are absorbed if they have the exact frequency required for electrons to excite to an allowed a higher level. When de-excitation subsequently occurs, it is not always by the same path so there is a decrease in the number of photons per Second of these frequencies getting through the gas. This leads to dark lines in the spectrum of light escaping the gas.
- 39How do atomic metals affect the absorption spectra of their atoms?As the proton number increases, so do the number off energy levels available to the outermost electron. In metals so many levels are available they are called energy bands. The outermost electron can de-excite to any level within the band. Photons emitted/absorbed are huge frequency band emission flash band absorption spectra.
- 40What is the role of the centre of a star?Radiates a continuous blackbody radiation, curve, which is mostly invisible but contains all visible frequencies. White light passes the outer layers of the star containing atomic hydrogen which is cool enough so Electrons eventually de-excite to the ground state.
- 41What spectra is produced from the de-excitations to the grounds state?UV spectra
- 42Eight requirements for a visible absorption spectra from a star.Temperature of approximately 5000 K so electrons in the gas are thermally maintained at n=2.
Full spectrum of light from the inner star passes through the outer star's atmosphere.
The stars atmosphere must contain hydrogen.
Electrons in the hydrogen atoms absorb photons of frequencies to go from n=2 to higher levels.
De-excitation may not occur via the same route so the intensity of these photons is reduced.
When de-excitation does occur along the same route, the light emitted is scattered in all directions not just outwards so the intensity of the frequencies is reduced in the direction towards the Earth.
Reduction in frequencies results in dark Balmer absorption lines within the continuous spectrum from the inner star.
Excitations occur from n=2 so the change in energy is smaller than for level one so all frequencies absorbed are lower than UV. - 43Draw an IvT graph for a Balmer seriesMore details on the next card
- 445 things to remember about the IvT graph for a Balmer seriesUneven temperature scale which decreases from left to right.
The most intense Balmer lines of are from stars with a surface temperature of approximately 10,000K
Stars with temperatures of less than 5000 K or more than 15,000 K have very weak Balmer lines.
Intensity of Balmer lines is affected by temperature.
The strongest Balmer Lines are emitted from stars in spectral class B or A. - 45What is the Issue with IVT graphs?For a given intensity there are two possible temperatures.
- 46How is This issue resolved?The spectra of elements are analysed. The peak intensities of absorption spectra of different elements are found to ascertain temperature.
- 47Name the following characteristics for each spectral class: temperature range; peak wavelength (colour);Balmer line spectra.This table
- 48Why are Balmer lines faint in an O-type star?At Very high temperatures electrons in the hydrogen atom are ionised and no de-excitations in the 4eV range can take place. Therefore the Balmer lines are very faint in O-type stars
- 49Why do Visible absorption lines still occur in hot stars?They come from Helium. To get a visible absorption spectra from helium, one electron must be ionised and the other is thermally maintained in a higher level than possible for hydrogen. This requires more energetic collisions from neighbouring gas molecules. Energy is gained from the heat, therefore a star must be incredibly hot to produce this spectra. Visible photons from the inner star are only absorbed it they pass through the atmosphere of a star at approximately 40,000K
- 50Why do visible absorption lines still occur in F and G stars?Visible photons from the inner star can be absorbed by electrons in metals at lower temperatures e.g. 7000 to 5000 K
- 51Why do visible absorption lines still occur in K and M stars?Metallic molecules have many levels available in the four electron volt range and can absorb visible photons from the inner star at even lower temperatures such as 4000 and 3000 K
Informationen
- Beschreibung
- Karteikarten am Astrophysics, erstellt von Whoknows am 30/05/2016.
- Erstellt von
- Whoknows
- Aufrufe
- 1
- Bewertung