Upload
thelawofscience
View
4.212
Download
1
Embed Size (px)
Citation preview
Images in Lenses
ConvergingDiverging
http://vle3rt7e.files.wordpress.com/2011/04/ww14_lens_flare_13_m.jpg
Lens
• A transparent material that is has at least one curved side
• Refracts light in a predictable and useful way
Types of Lenses
Converging Lens• makes parallel light rays
come together • Also known as convex
lens• Thicker at the center,
thinner at the edges
Types of Lenses
Diverging Lens• makes parallel light rays
move apart• Also known as concave
lens• Thinner in the center,
thicker at the edges
Lens Function• Change the appearance of
objects (image appears larger, smaller, upside down or misshapen)
• Magnify images
• Project images onto a screen
Terminology• Optical Centre (O) – centre of the lens; also the
point where the principal axis crosses• Axis of Symmetry – an imaginary vertical line
drawn through the optical center of a lens; perpendicular to principal axis
Optical Centre (O)
Focal Point
• Since lenses have 2 sides, they have a focal point on each side.
• The principal focus is where the light rays converge• A converging and diverging mirror has the principal
focus on different sides of the lens
Focal Point – Converging Lens
• Principal focus is on the opposite side of the lens as the incident rays
Principal FocusSecondary Principal Focus
Focal Point – Diverging Lens
• Principal focus is on the same side of the lens as the incident rays
• The focal point is virtual
Focal Length
• Focal length (f) is the distance between the principal focus and optical centre
• Distance from F to O, F to 2F, F’ to O, F’ to 2F are all equal.
• 2F and 2F’ are twice the distance away from the optical centre than the focus points.
FF’ 2F2F’ O
TerminologyPrincipal Focus (F)• A point on the principal axis where the light rays that are traveling
parallel to the principal axis appear to converge• In a converging lens it is on the opposite side as the incident rays• In a diverging lens it on the same side as the incident rays
Secondary Principal Focus (F’)• Focus that is on the opposite side as the principal focus, located the
same distance from the lens as F• In a converging lens it is on the same side as the incident rays• In a diverging lens it is on the opposite side as the incident rays
Focal Length (f)• distance from the principal focus to the axis of symmetry• Focal length is the same distance with the secondary principal focus
Light Rays with a Converging Lens
1. A light ray parallel to the principal axis will refract through the principal focus (F).
2. A light ray passing through the secondary principal focus (F’) will refract parallel to the principal axis.
3. A light ray through the optical centre (O) will keep travelling in the same direction without being refracted.
Light Rays with a Converging Lens
1. A light ray parallel to the principal axis will refract through the principal focus (F).
Light Rays with a Converging Lens
1. A light ray parallel to the principal axis will refract through the principal focus (F).
FF’
LOCATING AN IMAGE ON A CONVERGING LENS
2F’ 2F’
2F’ 2F’
2F’2F’
2F’2F’
Light Rays with a Converging Lens
1. A light ray parallel to the principal axis will refract through the principal focus (F).
2. A light ray passing through the secondary principal focus (F’) will refract parallel to the principal axis.
Light Rays with a Converging Lens
2. A light ray passing through the secondary principal focus (F’) will refract parallel to the principal axis.
FF’
LOCATING AN IMAGE ON A CONVERGING LENS
2F’ 2F’
2F’ 2F’
2F’2F’
2F’2F’
Light Rays with a Converging Lens
1. A light ray parallel to the principal axis will refract through the principal focus (F).
2. A light ray passing through the secondary principal focus (F’) will refract parallel to the principal axis.
3. A light ray through the optical centre (O) will keep travelling in the same direction without being refracted.
Light Rays with a Converging Lens
3. A light ray through the optical centre (O) will keep travelling in the same direction without being refracted.
FF’
LOCATING AN IMAGE ON A CONVERGING LENS
2F’ 2F’
2F’ 2F’
2F’2F’
2F’2F’
LOCATING AN IMAGE ON A CONVERGING LENS
• What happens when object is at F’?
2F’ 2F’
LOCATING AN IMAGE ON A CONVERGING LENS
1. Pick a point on the object (usually the top of the object)
2. Send any two light rays off the point on the object.
3. Determine the refracted rays. Light rays only refract when it hits the lens
4. Find the intersection of the light rays. If the rays do not intersection, extend the refracted ray until they do (exception: don’t do this for parallel light rays)
5. Use the point of intersection to location off an object is needed to locate its image.
LOCATING AN IMAGE ON A CONVERGING LENS
Ray 1 – travels parallel to the principal axis and is refracted through the principal focus (F)
LOCATING AN IMAGE ON A CONVERGING LENS
Ray 2 – travels through the optical centre (O) and continues straight without being refracted
LOCATING AN IMAGE ON A CONVERGING LENS
Ray 3 (optional since you only need 2 lines to form an intersection) – travels through the secondary principal focus (F’) and refracts parallel to the principal axis
LOCATING AN IMAGE ON A CONVERGING LENS
Draw the image given the point of intersection.
LOCATING AN IMAGE ON A CONVERGING LENS
5 Scenarios for the Object1. Beyond 2F’: Object is greater than 2 focal
lengths from the lens (do>2f)2. At 2F’: Object is at 2 focal lengths (do=2f)3. Between 2F’ and F’: Object is between 1 and
2 focal lengths from the lens (f<do<2f)4. At F’: Object is at the focal point (do=f)5. Between F’ and lens: Object is less than 1
focal length away from the lens (0<do<f)
Case 1 – Object beyond 2F’
Size Attitude Location Type
Reduced Inverted Between F and 2F Real
Converging LensObject beyond 2F’
Case 2 – Object at 2F’
Size Attitude Location Type
Same size Inverted At 2F Real
Size Attitude Location Type
Case 3 – Object between 2F’ and F’
Enlarged
Inverted Beyond 2F Real
Size Attitude Location Type
Case 4 – Object at F’
No Image Formed!
Size Attitude Location Type
Case 5 – Object between F’ and lens
Enlarged
Upright Same side as object
Virtual
Converging LensObject between F’ and Lens
CONVERGING LENSESThe first lens known to be used was a converging lens called a reading stone. Reading stones formed images that were upright and larger than the object.
How can a converging lens produce both upright and inverted images?
DIVERGING LENSES
DIVERGING LENSES
• The focal point is virtual• Thus the principal focus is on the same side
of the lens as the incident rays
DIVERGING LENSES
Light Rays with a Diverging Lens
1. A light ray parallel to the principal axis will refract through the principal focus (F).
2. A light ray passing through the secondary principal focus (F’) will refract parallel to the principal axis.
3. A light ray through the optical centre (O) will keep travelling in the same direction without being refracted.
Light Rays with a Diverging Lens
1. A light ray parallel to the principal axis will refract through the principal focus (F).
F’F 2F’2F O
Light Rays with a Diverging Lens
2. A light ray passing through the secondary principal focus (F’) will refract parallel to the principal axis.
F’F 2F’2F O
Light Rays with a Diverging Lens
3. A light ray through the optical centre (O) will keep travelling in the same direction without being refracted.
F’F 2F’2F O
LOCATING AN IMAGE ON A DIVERGING LENS
1. Pick a point on the object (usually the top of the object)
2. Send any two light rays off the point on the object.
3. Determine the refracted rays. Light rays only refract when it hits the lens
4. Find the intersection of the light rays. If the rays do not intersection, extend the refracted ray until they do (exception: don’t do this for parallel light rays)
5. Use the point of intersection to location off an object is needed to locate its image.
LOCATING AN IMAGE ON A DIVERGING LENS
• Q. Draw the ray diagram for this pencil to locate its image
F’F 2F’2F O
LOCATING AN IMAGE ON A DIVERGING LENS
F’F 2F’2F O
Ray 1 – travels parallel to the principal axis and is refracted through the principal focus (F)
LOCATING AN IMAGE ON A DIVERGING LENS
F’F 2F’2F O
Ray 2 – travels through the secondary principal focus (F’) and refracts parallel to the principal axis
LOCATING AN IMAGE ON A DIVERGING LENS
F’F 2F’2F O
Ray 3 (optional since you only need 2 lines to form an intersection)
travels through the optical centre (O) and continues straight without being refracted
LOCATING AN IMAGE ON A DIVERGING LENS
F’F 2F’2F O
Size Attitude Location Type
Reduced Upright Same side as object
Virtual
Diverging Lens
The image formed is always virtual, upright and smaller
Concave Lens Ray Diagrams
Ray 1 - travels from the tip of the object parallel to the principal axis. When it emerges from the lens, it appears to come from the principal focus (F)
Concave Lens Ray Diagrams
Ray 2 - travels from the tip of the object through the optical centre of the lens and is not refracted.
Concave Lens Ray Diagrams
The image occurs where these rays appear to intersect.