Telescopes Flashcards
Give some examples of waves that can be reflected:
- Sound waves are reflected off walls and buildings (echoes)
- Dophlins and bats use ultrasound (echolocation) to monitor their surroundings.
- Radio waves are reflected from surfaces within the atmosphere such as the ionosphere.
What are the rules of reflection?
- The angle of the incidence equals the angle of reflection.
- The incident ray, the reflected ray and the normal are all in the same plane.
What ray is going into the plate mirror?
The incident ray.
What ray is coming off of the plate mirror?
The reflected ray.
What is refraction?
Refraction is the bending of light rays at a surface. For example when entering or leaving a glass block.
What direction does the ray bend when light travels from air to glass?
When light travels from air to glass, the direction of the ray bends towards the normal. The angle of incidence is larger than the angle of refraction.
Why does refraction occur?
Refraction occurs because the speed of the wave changes as it passes through different materials.
What happens when light travels from a less dense material to a more dense material?
When light travels from a less dense material to a more dense material, it gets slower. This causes it to bend towards the normal.
What happens when light travels from a more dense material to a less dense material?
When light travels from a more dense material to a less dense material, it speeds up. This causes it to bend away from the normal.
What is a converging (or convex) lens?
A converging (or convex) lens is fatter in the middle.
What is a diverging (or concave) lens?
A diverging (or concave) lens is thinner in the middle.
What are converging lenses used for?
Converging lenses are used to form images in telescopes, cameras, projectors, binoculars and our eyes.
What is the focal length?
The distance between the centre of the lens and the focal point is called the focal length of the lens. The fatter the lens, the shorter the focal length.
What are the steps of ray diagrams?
- Draw a ray parallel to the principal axis.
- Draw a ray straight through the centre of the lens (it is not deviated).
- The image is formed where the two rays cross.
What can a converging lens produce?
A converging lens can produce both magnified and diminished images, depending on the position of the object.
What happens when the distance between the object and the lens is greater than 2f?
When the distance between the object and the lens is greater than 2f the image will be inverted, real and diminished.
What happens when the distance between the object and the lens is between f and 2f?
When the distance between the object and the lens is between f and 2f, the image will be inverted, real and magnified.
What is a magnifying glass?
When the object is closer to the lens than the focal length, the image is virtual, upright and magnified.
What are the lens in a modern refracting telescope?
In a modern refracting telescope, both the objective lens and the eyepiece are converging lenses. The objective lens produces an image of distant object at its focal point, and the eyepiece magnifies the image.
Why are reflecting telescopes much larger and easier to manoeuvre than refracting telescopes?
Reflecting telescopes can be much larger and are easier to manoeuvre than refracting telecopes. This is because a mirror has a much smaller mass than a bulky lens.
What does a simple reflecting mirror use?
A simple reflecting telescope uses a large concave mirror, a place mirror and a converging lens.
What does a concave mirror form?
The concave mirror forms an image of a distant object, which is then reflected towards the eyepiece using the plane mirror.
What are modern telescopes like?
Modern telescopes are huge. They are usually housed in observatories on high mountains, where there is little light pollution from cities. The air is also cooler, so there is less interference from the atmosphere.
Where is the Hubble Space Telescope?
The Hubble Space Telescope is orbiting Earth. There is no atmospheric interference in space and the telescope can produce images of very faint distance objects up to magnifications of about 5000.
