Flat Lens (Window)

n1n2

Incident ray is displaced, but its direction is not changed.

t

1

1

If 1 is not large, and if t is small, the displacement, d, will be quite small.

d

Converging LensAll rays parallel to principal axis pass through focal point F. Double Convex

P.A.

F

A beacon in a lighthouse produces a parallel beam of light. The beacon consists of a bulb and a converging lens. Where should the bulb be placed?

nlens > noutside

F

• At F

• Inside F

• Outside F

P.A.

F

Converging LensAll rays parallel to principal axis pass through focal point F. Double Convex

P.A.

F

A beacon in a lighthouse produces a parallel beam of light. The beacon consists of a bulb and a converging lens. Where should the bulb be placed?

nlens > noutside

F

• At F

• Inside F

• Outside F

P.A.

F

F

1) Rays parallel to principal axis pass through focal point.2) Rays through center of lens are not refracted.

3) Rays through F emerge parallel to principal axis.

Converging Lens Principal Rays

F

F

Object

P.A.

Image is (in this case): Real or Imaginary

Inverted or Upright

Enlarged or Reduced

1) Rays parallel to principal axis pass through focal point.2) Rays through center of lens are not refracted.

3) Rays through F emerge parallel to principal axis.

Converging Lens Principal Rays

F

F

Object

P.A.

Image is: real, inverted and enlarged (in this case).

Image

1) Rays parallel to principal axis pass through focal point.2) Rays through center of lens are not refracted.

3) Rays toward F emerge parallel to principal axis.

Diverging Lens Principal Rays

F

F

Object

P.A.

Image is (always true): Real or Imaginary

Upright or Inverted

Reduced or Enlarged

1) Rays parallel to principal axis pass through focal point.2) Rays through center of lens are not refracted.

3) Rays toward F emerge parallel to principal axis.

Diverging Lens Principal Rays

F

F

Object

P.A.

Image is virtual, upright and reduced.

Image

CONVEX LENS, OBJECT BEYOND 2F

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

CONVEX LENS, OBJECT BEYOND 2F

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

This could be used in a camera. Big object on small film

CONVEX LENS, OBJECT AT 2F

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

CONVEX LENS, OBJECT AT 2F

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

CONVEX LENS, OBJECT BETWEEN F AND 2F

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

CONVEX LENS, OBJECT BETWEEN F AND 2F

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

This could be used as a projector. Small slide on big screen

CONVEX LENS, OBJECT AT F

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

CONVEX LENS, OBJECT AT F

From the above diagram you can see that the image is (circle the correct choices):

NO IMAGE

CONVEX LENS, OBJECT BETWEEN F AND LENS

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

CONVEX LENS, OBJECT BETWEEN F AND LENS

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

This is a magnifying glass

CONCAVE LENS

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

CONVEX LENS, OBJECT BETWEEN F AND LENS

From the above diagram you can see that the image is (circle the correct choices):

ENLARGED, SAME SIZE, or REDUCED

INVERTED or ERECT

REAL or VIRTUAL

Converging LensWhich way should you move object so image

is real and diminished?

(1) Closer to lens(2) Further from lens(3) Converging lens can’t create real

diminished image.

F

F

Object

P.A.

Converging LensWhich way should you move object so image

is real and diminished?

(1) Closer to lens(2) Further from lens(3) Converging lens can’t create real

diminished image.

F

F

Object

P.A.

Which way should you move object so image is real?

1) Closer to lens

2) Further from lens

3) Diverging lens can’t create real image.

ACT: Diverging Lenses

F

F

Object

P.A.

Which way should you move object so image is real?

1) Closer to lens

2) Further from lens

3) Diverging lens can’t create real image.

ACT: Diverging Lenses

F

F

Object

P.A.

P.A.

F

Focal point determined by geometry and Snell’s Law: n1 sin() = n2 sin()

Fat in middle = ConvergingThin in middle = DivergingLarger n2/n1 = more bending, shorter focal length.n1 = n2 => No Bending, f = infinityLens in water has _________ focal length!

n1<n2

P.A.

F

Focal point determined by geometry and Snell’s Law: n1 sin() = n2 sin()

Fat in middle = ConvergingThin in middle = DivergingLarger n2/n1 = more bending, shorter focal length.n1 = n2 => No Bending, f = infinityLens in water has larger focal length!

n1<n2

1) Rays parallel to principal axis pass through focal point.2) Rays through center of lens are not refracted.

3) Rays through F emerge parallel to principal axis.

Assumptions: • monochromatic light incident on a thin lens.

• rays are all “near” the principal axis.

Converging Lens Principal Rays

F

F

Object

P.A.

Image is real, inverted and enlarged

Image

Preflight 19.1A converging lens is used to project a real image

onto a screen. A piece of black tape is then placed over the upper half of the lens.

How much of the image appears on the screen?

Java

A converging lens is used to project a real image onto a screen. A piece of black tape is then placed over the upper half of the lens.

Still see entire image (but dimmer)!

Lens Equation

cm 1011

cm 151

id

F

F

Object

P.A.

do

di

f

Image

1do

1di

1f

• do = distance object is from lens:

• Positive: object __________ lens

• Negative: object __________ lens

• di = distance image is from lens:

• Positive: ________ image (behind lens)

• Negative: ________ image (in front of lens)

• f = focal length lens:• Positive: ___________ lens

• Negative: ___________ lens

di =

m =

Lens Equation

cm 1011

cm 151

id

cm 30id

o

i

dd

m 2

F

F

Object

P.A.

do

di

f

Image

1do

1di

1f

• do = distance object is from lens:

• Positive: object in front of lens

• Negative: object behind lens

• di = distance image is from lens:

• Positive: real image (behind lens)

• Negative: virtual image (in front of lens)

• f = focal length lens:• Positive: converging lens

• Negative: diverging lens

Multiple LensesImage from lens 1 becomes object for lens 2 1

f1 f2

2

Complete the Rays!!

Multiple Lenses: Magnification

f1 f2

do = 15 cm

f1 = 10 cm

di = 30 cm

f2 = 5 cm

L = 42 cm

do=12 cm

di = 8.6 cm

1m

2m 21mmmnet

1 2

Net magnification:mnet = m1 m2