P7: Light, Telescopes and Images
Terms in this set (18)
What is the speed of a wave affected by?
The medium it passes through.
What is optical density?
A measure of the extent to which a substance transmits light.
What is Refraction?
The bending of a wave as it passes at an angle from one medium to another.
Why does refraction occur when a wave passes from one medium to one with a different density?
The speed of the wave changes but because the frequency stays constant, wavelength changes which causes a change in direction.
What does a converging lens do?
Use refraction to bend the light rays coming out of it inwards. This has the effect of focusing the light to a point called the focal point. Causes parallel rays of light to come in to focus.
How do the light rays from far away astronomical objects reach us?
When they are so far away the light rays that reach us from them are effectively parallel.
What does the light being faint from very distant stars mean?
a large telescope will be needed to collect enough light to make a visible image.
What will a simple optical telescope have?
2 converging lenses of different powers .
Which will the more powerful lens be in a simple optical telescope?
The eyepiece lens.
What does the objective lens in a telescope do?
Focuses the light to the focal point of the lens. The eyepiece lens produces a magnified image of the image from the objective lens which the viewer can see.
What is used in a reflecting telescope instead of a convex objective lens?
a concave mirror is used to collect parallel rays from the object and form an image at the focal point. Then the convex eyepiece lens is used to magnify this image for the viewer.
What do concave mirrors do?
focus light at a focal point using reflection, not refraction.
What are used in professional telescopes and why?
Mirrors are used instead of lenses in large, professional telescopes because an objective lens can have a maximum diameter of approximately 1 metre before it begins to sag, whereas a mirror of several metres in diameter can be used.
What are other advantages of using a mirror in a telescope?
-They can be made very smooth - resulting in undistorted images.
-Suitable reflectors can be used to focus all types of electromagnetic radiation.
-Mirrors reflect rays of all colours in the same way.
What is diffraction?
When waves move through a narrow gap or past an obstacle, they spread out from the edges.
When is diffraction most significant?
When the gap or obstacle is very small compared to the wavelength of the light.
What is Dispersion?
Splitting of light in to different spectral colours or wavelengths.
Which coloured light is refracted the least in a block and which is refracted the most?
Red light is refracted the least
violet light is refracted the most.