Astrophysics 01 - Lenses

Define Focal Length.

A fixed property of a lens; the distance away from a screen that a lens bust be for a distant object to be focused on the screen.

Define lens power.

A measure of the curvature of a lens. A lens with more curvature has a smaller focal length.

Give the equation relating lens power and focal length.

Lens Power (Dioptre) = 1 / focal length (m)

P = 1 / f

Give the two types of lenses, and how they effect light.

Convex - converge light

Concave - diverge light

Define a real image.

An image which can be projected onto a screen, i.e. the image is focused on the opposite side of the lens to the object.

Occurs when an object is more than one focal length away from the lens.

Define a virtual image.

An image which cannot be projected onto a screen. The image is focused on the same side of lens as the object.

Occurs when an object is less than one focal length away from the lens.

Explain how to draw a ray diagram.

Give the lens equation.

1/focal length = 1/ distance from lens to object + 1/ distance from lens to image

1/f = 1/u + 1/v

Give the equation for magnification.

magnification = distance from lens to image / distance from lens to object

m = v / u