Lense Lesson

 Objectives:

Actions of Lenses:
5.1 illustrate the effect of converging and diverging lenses on a beam of parallel rays;


5.2 define the terms:
      (a) principal axis;
      (b) principal focus;
      (c) focal length;
      (d) focal plane;
      (e) magnification;


Image Formation: 
5.3 differentiate between real and virtual images;
5.4 apply the equations for magnification.
5.5 determine the focal length of a converging lens.

Contents: 

Simulators: 

• Concave Lens
• Convex lens

Definition: 

A lens is a piece of specially shaped transparent material that can form focused images of objects.

A convex or converging lens is one that is thicker at its center. It can converge parallel rays of light to produce a real image.

A concave or diverging lens is one that is thinner at its center. It can diverge parallel rays of light to produce a virtual image.

The optical center, O, of a lens is the point at the center of the lens through which all rays pass without deviation.

The principal axis of a lens is the line that passes through its optical center and is perpendicular to the faces of the lens.

The principal focus, F, of a lens is the point on the principal axis through which all rays parallel and close to the axis converge, or from which they appear to diverge, after passing through the lens.

• The principal focus of a converging lens is a real focus, since rays actually converge there.
• The principal focus of a diverging lens is virtual, since the rays diverge as they leave the lens and must be produced backwards to give the position of the image.
  

The focal length, f, of a lens is the distance between its optical center and its principal focus.

The focal plane of a lens is the surface perpendicular to its principal axis and containing its principal focus.

Drawing and Locating Images Form by Converging & Diverging Lenses 

Converging/Convex Lens:

• Ray passing through C passes straight through without a change in direction.

• Ray parallel to principal axis passes through lens and changes direction and passes through F.

• Ray passing through F initially reaches lens and passes out parallel to principal axis.

Diverging/Concave Lens:

• Ray passing through C passes straight through without a change in direction.