P7 Page 7 Flashcards
What does the amount diffraction depend on?
It depends on the size of the gap relative to the wavelength of the wave.
What is diffraction?
When the edges of the waves pass through a gap or past an object.
The narrower the gap,or the longer the wavelength, the more or less do waves spread out?
The more
When is maximum diffraction reached?
When the gap is the same size as the wavelength.
Why is a bigger aperture for faint sources?
Because a bigger aperture collects more light and forming a better image.
What is ‘aperture’?
The diameter of the objective lens.
Why are big concave mirrors used instead of large lenses?
Large lenses are difficult and expensive to make, while big mirrors are much easier to make accurately.
What happens if a telescope is smaller than the wavelength of radiation?
Because all waves diffract through a gap,radiation entering a telescope spreads out at the edges of the aperture- causing the image to blur.
What would you see through an image if you used to small of an aperture?
The dot would be dimmer and surrounding by rings which get dimmer the further from the image they are.
How do you prevent diffraction of the telescope?
To have an aperture that’s much wider than the wavelength of radiation you want to look at. So little diffraction occurs and you get a sharp image.
What is a diffraction grating?
A diffraction grating has very narrow slits-small enough to diffract light.
What happens when white light goes through a diffraction grating?
The different wavelengths of coloured light are all diffracted but by different amounts. This creates a spectrum of different coloured light, as shown below.
what do astronomers use a diffraction grating for?
They use the spectra to analyse light coming from stars.
