Embed Size (px)
Citation preview
The Properties of Light
• Linear Propagation
• Refraction
• Reflection
• Diffraction
• Polarization
The Characteristics of Images
• TYPE
• ORIENTATION
• SIZE
TYPE OF IMAGE
• Real vs Virtual– Real Images can be seen on a piece of paper or screen
placed because the focal point is in front of the mirror or behind the lens.
– Virtual Images can not be seen on a piece of paper or screen, because the focal point is behind the mirror or in front of the lens. Virtual images are images which are formed in locations where light does not actually reach; it only appears to an observer as though the light were coming from this position.
ORIENTATION OF IMAGE
• Inverted vs Upright– Inverted images are upside-down.– Upright images are right-side up.
SIZE OF IMAGE
• Smaller, Larger, or Same Size– Smaller Images are reduced in size compared to
the actual object.– Larger Images are enlarged in size compared to
the actual object.– Same Size Objects are unchanged in size
compared to the actual object.
• Size is also discussed quantitatively in terms of Magnification.
Magnification (m)
The ratio of the size of the image to the size of the actual object.
The Magnification equation:
m = hm = hii/h/hoo = - d = - dii/d/doo
hhii is the height of the image, is the height of the image,
hhoo is the height of the object, is the height of the object,
ddoo is the distance of the object from the lens or mirror, is the distance of the object from the lens or mirror,
ddii is the distance of the image from the lens or mirror. is the distance of the image from the lens or mirror.
Reflection
Light follows the same law of reflection as all other waves.
Both angles are measured from the normal to the surface at the point of incidence.
Glare- bright light that reflects to your eyes from the surface of smooth objects
Diffuse vs Regular Reflection
• Diffuse reflection is produced when the rays are reflected in many different directions by an uneven surface.
• Regular reflection is produced by a very smooth, flat surface. The rays leave the surface parallel to each other.
Plane Mirrors
• Plane mirrors are uniformly flat. The image is sent back virtual, erect, same size, and laterally inverted.
•The image of the object looks like it is the same distance in back of the mirror as the actual object is in front of the mirror.
Reflection from a Plane Mirror
Types of Curved Mirrors
• Curved mirrors can either be concave or convex.– Concave mirrors focus the light at a point in
front of the mirror. They reflect light from the inner surface. Also called CONVERGENT.
– Convex mirrors spread the light out. They reflect light from the outer surface. Also called DIVERGENT.
Features of Curved Mirrors
• Principal Axis: the straight line perpendicular to the surface of the mirror at its center.
• Focal Point: the location where the parallel rays of light from the source meet, or converge.
• Focal Length: the distance from the Focal Point to the mirror along the Principal Axis.
• Center of Curvature: twice the distance of the focal point to the mirror surface.
A Concave Mirror
The image formed is dependent upon where the object is located relative to the focal point of the
concave mirror.
A diverging mirror always makes a virtual, upright, smaller image.
Marching Soldiers
• The line of students approach the boundary between the two medium (the masking tape). An arrow is used to show the general direction of travel for the group of students in both medium. Observe that the direction of the students changes at the "boundary."
Refraction
The change in direction or bending of light at the boundary between two media.
Refraction only occurs when the angle of incidence is non-zero.
Optical Density• The optical density of a material relates to the
sluggish tendency of the atoms of a material to maintain the absorbed energy of an electromagnetic wave in the form of vibrating electrons before reemitting it as a new electromagnetic disturbance.
• The more optically dense which a material is, the slower that a wave will move through the material.
A property of the medium, expressed mathematically as:
n = sin i/sin r and n = c/v
i is the angle of incidence from a vacuum
r is the angle of refraction in a new medium
c is the speed of light in a vacuum (3 x 108 m/s)v is the speed of light in a specific medium.
The Index of Refraction
Refraction From less dense to more dense: light
travels more slowly and the angle of refraction is smaller than the angle of
incidence. FST = Fast to Slow, Towards Normal
From more dense to less dense: light travels more quickly and the angle of refraction is greater than the angle of
incidence. SFA = Slow to Fast, Away From
Normal
Practice Refraction
A ray of light bends in such a way that the ratio of the sine of the angle of incidence to
the sine of the angle of refraction is a constant.
This constant is called
the index of refraction, n.
Snell’s Law
Snell’s Law
For a ray traveling from one medium into another medium:
ni sin i = nr sin r
Find the fastest Path
• A direct path is not always the fastest way to get to the end point.
Race
Fish View
Total internal reflection
Usually when light travels from one material to another, part of the light is reflected and part is refracted.
In total internal reflection, all of the light is reflected.
Two Criteria for T.I.R.
1. Light must pass from a more optically dense to less optically dense medium.
2. There are only specific angles of incidence, called the critical angle, which is different for each medium.
To find the critical angle, use Snell’s Law, substituting 90º for r.
Increasing Angle of Incidence
An Application of T.I.R.
Fiber optics.
Telephone, radio,video, and television signals can now be sent with light beams rather than electric currents.This is more energy-efficient.
Demonstrations of T.I.R.
Other Applications of Refraction
Mirage – an illusion caused by the refraction of light waves because light travels faster in warm air.
Prism – triangular piece of glass that shows light refraction.
Dispersion – the separation of light into a spectrum by refraction (usually using a prism).
Rainbows - after a rainstorm passes, sunlight refracts in the many small raindrops in the air.
Why are different colors separated?
• The shorter the wavelength, the more the light slows down when entering a new medium.
• Violet has the shortest wavelength, so it slows down the most and bends the most.
Dispersion and RainbowsDispersion
Why are skies blue?
• The two most common types of matter present in the atmosphere are gaseous nitrogen and oxygen.
• These are most effective in scattering the higher frequency portions of the visible light spectrum
• violet light is scattered most easily, followed by blue light, green light, etc
• White light (ROYGBIV) passes through our atmosphere
• High frequencies (BIV) become scattered by atmospheric particles
• Lower frequencies (ROY) are most likely to pass through the atmosphere without a significant alteration in their direction
• the skies are illuminated with light on the BIV end of the visible spectrum.
• Thus, we view the skies as being blue in color.
Why is the sun yellow?
• Non-scattered light (ROY) passes through the atmosphere and reaches our eyes in a rather non-interrupted path to our eyes as we sight directly at the sun.
• The sun appears yellow during midday due to the direct passage of dominant amounts of yellow frequencies through our atmosphere and to our eyes.
Why Are Sunsets Red?
• As the sun approaches the horizon line, sunlight must traverse a greater distance through our atmosphere; this is demonstrated in the diagram.
• As the path which sunlight takes through our atmosphere increases in length, ROYGBIV encounters more and more atmospheric particles.
• There is greater and greater amounts of yellow light scattered, leaving concentrations of red and orange frequencies of light.
• Thus, sunsets have a reddish-orange hue. • The more particles in the atmosphere (clouds,
pollution, etc.), the more pronounced the effect of a red sunset.
