2572502
Description
Flashcards by Josh Price, updated more than 1 year ago
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Created by Josh Price
about 9 years ago
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| Question | Answer |
| What is the speed of waves affected by? | The medium they are travelling through. |
| How does refraction lead to the formation of an image by a convex/converging lense? | Because the lense is fatter in the middle than at the edges, the bends at different speeds. The light which enters at the bottom, crosses to the top. |
| Will a more powerful lens have a curvy surface of a less curvy surface? | More curvy because a lense with a short focal length bends the rays of light more. |
| What is the equation for calculating the power (in dioptres) of a lens? | 1 --------------------------- focal length (m) |
| Why does light from astronomical objects reach Earth as effectively parallel sets of rays? | Because the objects are so far away. |
| What are the features of a simple optical telescope? | They have two converging lenses of different powers, with the more powerful lens as the eyepiece. |
| What are the optical elements of a telescope? | a) An objective lens or mirror to collect light from the object being observed and form an image of it. b) An eyepiece which produces a magnified image of the image from the object that is viewed. |
| What is the equation for calculating the angular magnification of a telescope? | Focal length of objective lens ----------------------------------------------------- Focal length of eyepiece lens |
| Why do most astronomical telescopes have concave mirrors, not converging lenses, as their objectives? | - A mirror reflects rays of all colours in exactly the same way. - Its weight can be supported from the back as well as the sides, so that it doesn't sag. - A mirror can be made very smooth so that the image is not distorted. - Reflectors can be made to focus most types of electromagnetic radiation. |
| How do concave mirrors bring a parallel beam of light to a focus? | The angle of incidence equals the angle of reflection, so rays parallel to the axis of the reflector are reflected to the focus. |
| Why are large telescopes needed to collect weak radiation from very distant sources? | Because the larger the telescope, the more radiation can be detected. This radiation can help astronomers to find out more about its source. |
| What is diffraction? | The effect of waves spreading out from a narrow gap. When doing so, they curve a little at their edges. |
| How can diffraction be increased? | - By increasing the wavelength of the wave. - By narrowing the aperture (gap). |
| Why does the aperture of a telescope have to be very large? | Because radiation is diffracted by the aperture of a telescope. The aperture must be very much larger than the wavelength of the radiation detected to produce sharp images. |
| How can a spectrum be produced by refraction in a prism? | Because the colour of light depends upon its frequency (and therefore wavelength). Red has the lowest frequency, and violet has the highest (shortest wavelength). Dispersion happens through a prism because the light travels through the glass at different speeds, which splits up the light so that different colours are refracted through different angles. |
| How else can a spectrum be produced? | By a diffraction grating, which is a set of very narrow evenly spaced parallel lines ruled on a thin sheet of glass. When light shines on the grating, different colours emerge at different angles to produce several spectra. |
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