15.2 Lensespp. 568 -579

Mr. Richter

Agenda

Review HW Introduction to Lenses Notes:

Types of Lenses Converging Lenses

Distances and Images Diverging Lenses

Objectives: We Will Be Able To… Determine whether an image produced by a lens is

real or virtual. Determine the orientation and magnification of an

image produced by a lens.

Warm-Up:

Where do you see lenses used? What purpose do they serve?

Types of Lenses

Lenses

Curved objects change the direction of light.

Like mirrors, lenses form images, but by refraction instead of reflection.

Images may be real or virtual, depending on distance from the focal length (F).

Types of Lenses

Converging Thicker in the middle than

it is at the rim.

Edges converge.

Diverging Thicker at the rim than it

is at the middle.

Edges diverge.

Converging Lenses

Converging Lens Image: Object at Infinity.

All rays of light converge on the focal point. Focuses light energy in one place. No image forms.

Good for burning holes and not much else.

Converging Lens Image Object Closer than Infinity to the Focal Length

Image is real and inverted, and can be projected on to another surface.

Converging Lens Image Object Closer than Infinity to the Focal Length

Image is smaller than object.

Seen in: Camera lens Human eye

Corrective Vision: Farsightedness When the eye cannot move its focal point close

enough, nearby images are blurry. This hyperopia, or farsightedness, can be corrected by

a converging lens.

Converging Lens Image Object Closer than Twice the Focal Length

At between twice the focal length and the focal length:

Image is magnified. Seen in:

movie or slide projector

Converging Lens Image Object At the Focal Length

Rays of light never converge. Light is projected an infinite

distance way. No image forms.

Seen in light houses and search lights

Converging Lens Image Object Closer than the Focal Length

Image is virtual. Image is projected larger

on the same side of the lens as the object.

Good for: magnifying glass binoculars

Recap Images of Converging Lenses

Object Distance Real or Virtual MagnificationInfinity N/A: Point Image N/AGreater than focal length

Real and inverted. Image is smaller than object.

At focal length N/A: Image is projected to infinite distance.

N/A

Closer than focal length.

Virtual and upright.

Larger image the closer to the focal point.

Diverging Lenses

Diverging Lenses Diverging lenses only produce virtual

images. Used to produce upright images that

are smaller than the original but a wider viewing angle.

Like: viewfinders in (older) cameras.

Corrective Vision: Nearsightedness When the eye’s focal point is too close, faraway

images are blurry. This myopia, or near sightedness, can be corrected by

a diverging lens.

Wrap-Up: Did we meet our objectives?

Determine whether an image produced by a lens is real or virtual.

Determine the orientation and magnification of an image produced by a lens.

Homework

p. 587-588 #15-18, 21