Optical Telescopes Flashcards
What is the principal axis of a lens?
An imaginary line through the centre of the lens, at 90°
What happens to all light rays incident on a converging lens, parallel to the principal axis?
The converge onto a single point
“Principal Focus”
What happens to all parallel light rays incident on a converging lens?
They converge onto a single point on the focal plane
What is the focal length, f?
The distance between the lens axis and the focal plane
What is the lens axis?
The plane of the centre of the lens
Draw a converging lens for axial rays
Draw a converging lens for non-axial rays
What are the two types of images?
Real and virtual
What defines a real image?
The light rays are actually there, and the image can be captured on a screen
How is a real image formed?
Light rays from an object are made to pass through another point in space
What defines a virtual image?
The light rays aren’t actually where the image appears to be. The image cannot be captured on a screen
How is a virtual image formed?
When light rays from an object appear to have come from another point in space
What kind of image can a converging lens form?
Both real and virtual
What determines whether a virtual or real image is formed for a converging lens?
The distance of the object from the lens
Where will the image of an object sit, if the object is on the principal axis?
On the principal axis
If an object doesn’t sit on the principle axis, how do you find where the bottom of the image will be formed?
Draw two rays from the bottom of the object as well as the top
Draw a ray diagram for light passing through a converging lens (from an object)
If the object is further than the focal length away from the converging lens, what kind of image is formed?
Real image
At what distance from a converging lens is the object, for a real image to be formed?
Further that the focal length away
If the object is closer than the focal length away from the converging lens, what kind of image is formed?
Virtual image
At what distance from a converging lens is the object, for a virtual image to be formed?
Closer than the focal length away
When you draw a ray diagram for a converging lens, what two rays do you draw?
One parallel to the principal axis (therefore refracted through the principal focus on the other side of the lens)
One passing through the lens’ centre (therefore no refraction)
On a ray diagram for a converging lens, how do you determine if the image will be virtual?
If the refracted rays on the other side of the lens will never meet
What and where is the lens equation in the formula book?
Medical Physics: 1/f = 1/u + 1/v