Telescopes Flashcards
What is a Convex / Convering Lens
A lens that focuses incident light
Describe a real image being formed from a Convex Lens
What is a Concave / Diverging Lens
A lens that spreads out incident light
Describe a diagram of light on a concave lens
What is the Principal Axis
The line passing through the centre of the lens at 90º to its surface
What is the Principal Focus
- In a converging lens - the point where incident beams passing parallel to the principal axis will converge
- In a diverging lens - the point from which the light rays appear to come from (This is the same distance either side of the lens)
What is the Focal Length
The distance between the centre of a lens and the principal focus
What is a Real Image and a Virtual Image
- Real image - formed when light rays cross after passing through the lens, can be formed on a screen
- Virtual image - formed on the same side of the lens. The light rays do not cross, so a virtual image cannot be formed on a screen
What is the Lens Formula
- 1 / u + 1 / v = 1 / f
- u is the distance of the object from the centre of the lens
- v is the distance of the image from the centre of the lens
- f is the focal length of the lens
What are the words used to describe an image that is formed
- Real or Virtual
- Magnified or Diminished
- Upright or Inverted
Describe the ray diagram for an object that is beyond 2F and describe the image’s apperance
Real, Inverted and Diminshed
Describe the ray diagram of an image that is very close to the lens and describe the image’s apperance
Virtual, Upright and Magnified
Describe the ray diagram of an image that is fairly close to the lens (between 2F and F) and describe the image’s apperence
Real, Inverted and Magnified
Describe the ray diagram of an image that is exactly 2F from the lens and describe the image’s apperence
Real, Inverted and same size
What is the Equation for Angular Magnification in Normal Adjustment
M = Angle subtended by the eye to the image/ Angle subtended by the eye to the object
What is the Equation for Angular Magnification in terms of the focal length
M = f0 / fe
Only used if both angles in other equation are below 10º