Karteikarten
Telescopes
Karten in diesem Stapel (24)
- 1What is a real imageThe light rays are actually there and can be captured on a screen. If virtual they cannot be captured on a screen as they appear to have come from another point to where they have.
- 2CCD'sCCDs are silicon chips divided into millions of identical pixels.
When light shines on the pixels, electrons are liberated from the silicon proportional to the brightness of the light. The electrons are stored in potential wells and released when they have been exposed to the light for the desired time. The charge is processed and converted into a digital signal. - 3Quantum efficiencyThe incoming photons of light release electrons in the silicon CCDs. Electrons are released by more than 70% of the photons which means the QE is greater than 70%. The eyes QE is 1%
- 4What is the resolving power of a telescopeThe smallest angular separation at which two points can be distinguished. It is when the minima and maxima of 2 diffraction patterns correspond.
- 5RefractorsGlass refracts different colours of light by different amounts so the image for each colour is in a slightly different position. Called chromatic aberration
Any impurities in the glass scatter and absorb light so faint images are not seen.
Large lenses are heavy and can only be supported from the edges so shape can become distorted.
For large magnification focal lengh of objective must be very long so a long telescope will be produced. . - 6ReflectorsReflectors can be made much larger than refractors because the mirror can be supported from behind while a large lens is likely to break under its weight due to only being supported from the edges. This benefits collecting power and resolving power
Mirrors suffer from spherical aberration instead of chromatic aberration.
The secondary mirror and the spider holding it diffract light as it passes, leading to poor quality image - 7Radio telescopeA wire mesh can be used instead of a mirror due to radiowaves long wavelength. EM radiation is reflected and focused by the dish onto an antenna at the focal point. A pre amplifier and a second amplified amplifies the signal without adding too much noise. A computer then creates a falsecolour imageof radio signals. Most radio telescope are manoeuvrable to track waves.
Wire mesh must be smaller than 20th of the wavelength it is detecting - 8Resolving power of radio telescopeDue to the long wavelengths of the radio waves the resolving power is much weaker. The diameter to compete with optical would be far too large. Therefore we link lots of smaller radio telescopes together to be combined to produce a single image.
- 9Benefits of a radio telescopeBeing able to make the telescope out of wire mesh makes it much easier and much cheaper to construct.
Due to the longer wavelengths, the imperfections caused by the shape of the dish are much smaller so it does not need to be as precisely constructed. - 10IR and UV telescopesThey use a parabolic mirror to focus radiation onto a detector and a CCD is used to detect signals. IR doesn't need to be as perfectly shapes due to longer wavelength however UV needs to be more precise.
As IR telescopes produce their own IR due to temperature they must be cooled to very low temperatures by liquid helium or refrigeration units. - 11X-ray telescopesX-rays don't reflect off surfaces light other EM but only grazing a mirror surface. A series of nested mirrors can gradually focus X-rays onto a detector. Called a grazing telescopes
- 12Telescope positioningOur atmosphere only lets in certain wavelengths of EM. Optical and radio telescopes can be used at earth. A few wavelength of IR can be viewed on top of a dry mountain.
UV, X-ray and other IR telescopes have to be attached to high altitude weather balloons or aeroplanes. Can also launch telescope into space above atmosphere. - 13What determines resolving powerThe Rayleigh criterion and the resolving power of the detector e.g. how many pixels on a CCD
- 14Collecting powerProportional to the area of the dish, or the square of the diameter.
- 15What image is formed when the object is beyond 2FThe image is real, inverted and diminished
- 16What image is formed when the object is at 2FThe image is real, inverted and the same size as the object
- 17What happens when the object is between F and 2FThe image is real, magnified and inverted
- 18What happens when the object is between F and the lensThe image is virtual, upright and magnified.
- 19What can you assume about parallel light coming from an objectThey all come from the same point of the object.
- 20How to convert between radians and degreesradians=degrees x 2π/ 360
- 21angle subtendedθ= height of object/ distance to the object
Therefore alpha= h/fe
beta= h/fo - 22Rayleigh criterionTwo objects will be just resolved if the centre of the diffraction pattern of one image coincides with the first minimum of the other.
- 23What can cause issues with radio telescopesMan made interference can cause big problems. Radio transmission, mobile phones, satellite TV's and even microwaves contribute to making detecting objects in space difficult.
Radio telescopes are built away from populations to limit the microwaves radio waves. - 24Why are many modern telescopes in spaceBecause a lot of EM waves are absorbed by the atmosphere
The light pollution and other interference at ground level
The effect that the atmosphere has on light as it passes through it
Informationen
- Beschreibung
- Alevel physics Karteikarten am Telescopes, erstellt von Catrina Bowman am 23/05/2015.
- Erstellt von
- Catrina Bowman
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- 6
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