Light, telescopes and images Flashcards
What does a change in wave speed do and cause?
When a wave changes speed, it changes wavelength as the frequency cannot change, this may cause a change in direction which is referred to as refraction
How does refraction cause the formation of an image through a convex/converging lens?
The light reflected or emitted from an object will enter the entire lens, each section at a different angle. Because each section is entered at a different angle and the width of the lens is different throughout the lens, the light that enters is refracted by different amounts causing all the light to be refracted inwards to a single point where the image can be viewed
How does the curvature of a lens relate to its power?
The more curved the surface of a lens is, the more powerful it is
How is the power of a lens calculated?
Power (dioptres) = 1 / focal length
How does the distance light from stars travel affect how light reaches us?
The light travels so far it arrives in practically parallel sets of rays
In an optical telescope which lens is more powerful?
The eyepiece lens is more powerful than the objective lens
What are the two elements and their functions in an optical telescope?
An objective lens/ mirror to collect light from the object being observed.
An eyepiece lens which produces a magnified image of the image from the objective lens that we can view
How can magnification be calculated?
Focal length of objective lens / focal length of eyepiece lens
Why are concave mirrors typically used over converging lenses as the objective?
Mirrors are cheaper and easier to produce on a large scale.
There is more chance of an impurity or problem in a lens if a large one is made, compared to the usual clarity of large mirrors
How do concave mirrors focus light?
Light enters the telescope as parallel rays as it has come a long way and the curvature of the mirror reflects all these rays onto a second mirror at 45* that reflects the collected rays together as an image to the eyepiece
How does diffraction occur and what is it?
Diffraction occurs when a wave of radiation passes through a gap the same size as the wavelength of the wave, it causes the radiation to come out as curves and distorts the image the radiation showed
What must be done to the aperture of a telescope to produce sharp images?
Radiation is diffracted by the aperture of a telescope, therefore the aperture must be much larger than the wavelength of the radiation to produce a crisp image
Why can a spectrum be produced using a prism?
If white light is shot at a prism, then the varying wavelengths of the light in white light will become refracted by different amounts in this new medium and so the light that leaves the prism is spread out and separated
What happens to a wave when it travels through a different medium?
The wave speed will change depending on the density and structure of the new medium compared to the the previous
