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Transcript
Light
Warm-up
Why do some objects make shadows, while others do not?
Warm-up
Answer
Opaque objects make shadows because light does not pass through them. The shadow is in the area where light would have been had it passed through the object. objects you can see through do not block the light, so there is not shadow.
Light, Color, & Objects
- When referring to color we often refer to the electromagnetic spectrum that is visible to the human eye.
- Materials that transmit most of the light that strikes it, is transparent.
Light, Color &
Objects
Transparent
Transparent
- A material that transmits most of the light that strikes it is transparent.
- You can see through a transparent object, such as a window pane or the plastic wrap on a package.
Translucent
- A translucent material scatters the light that passes through it.
- You might be able to see through translucent material, but the image will be blurry.
- Ex. waxed paper & gelatin dessert are translucent materials.
Translucent
Opaque
- A material that reflects or absorbs all of the light that strikes is opaque.
- Ex. a book, a marshmallow, and a hippopotamus are all opaque.
Opaque
The Color of Objects
The color of Objects
- Recall: White light is a mixture of all of the colors in the rainbow.
- White light shines on a white object, all the colors of light are reflected.
- Colored objects, some of the colors are reflected, and some are absorbed.
The color off...
More about color
- the color of an opaque object is the color of light that the object reflects.
- it absorbs all colors.
- The color of a transparent or a translucent object is the color of light that passes through it.
- Ex. the color of a clear, green drinking glass is green because green light is the only color of light that passes through it.
Why does snow appear white?
Check Point
It reflects
all colors of light.
Answer
Photography & Color Filters
- Color filters can be used on this image of the Golden gate Bridge to bring out certain colors or create dramatic moods.
SUBTOPIC 2
Reflecting Light
Reflecting Light
- Light can be reflected
- The reflection of light occurs when rays of light bounce off a surface.
- Reflected light is what produces your image in a mirror, but reflected light also produces a distorted image or no image at all in the surface of rippling water on a lake.
- This depends whether the light undergoes regular reflection or diffuse reflection.
Diffuse Reflection
- In diffuse reflection, parallel rays of light hit an uneven surface.
- The angle at which each ray hits the surface equals the angle at which it reflects.
- the rays , don't bounce off in the same direction because the light rays hit different parts of the surface at different angles.
Regular Reflection
- Regular reflection occurs when parallel rays of light hit a smooth surface.
- As a result, the reflection is a clear image.
Regular
1. Convex Mirrors
Three different types...
- A convex mirror is like the outside of the bowl because it is a mirror with a surface that curves outward.
- If you look at an image on the outside of the bowl, it is smaller than the image in a plane mirror.
Look at the optical axis & the focal point of the mirror...
To
understand...
- The optical axis is an imaginary line that divides a mirror in half.
- The focal point is the location at which rays parallel to the optical axis reflect and meet.
- The light reflects off the curved surface such that the image appears to come from a focal point behind the mirror.
2. Concave Mirrors
#2
- A concave mirror curves inward.
- The image formed from a concave mirror depends on whether the object is between the focal point & the mirror or farther away from the mirror than the focal point.
- if the object is farther from the mirror than the focal point is, then reflected light rays cross one another, & the image is inverted, this is a real image.
- If the object is between the focal point & the mirror, then the image is not inverted and is larger than the actual object, this is a virtual image.
Large telescopes
Telescopes
- Large telescopes are built with mirrors.
- The 5.1 -meter Hale telescope at Mount Palomar, in southern California, was the largest telescope in the world for more than 40 years.
- M51 taken with 200" Hale
If a mirrored image is inverted, what type of image is it?
Check Point
Answer
real
3. Plane Mirror
#3
- The mirrors you have at home are most likely plane mirrors.
- The image seen in your mirror is called a virtual image, which is an image that forms where light seems to come from.
- An image on a plane mirror, is upright and the same size as the object that formed the image, but the right and left sides of the image are reverse.
Light bends/refracts
Lenses
- A lens is a curved piece of transparent material that refracts light.
- Ex. Eyeglasses are lenses that correct your vision.
- Lenses are also used in devices designed to serve other functions, such as telescopes and cameras.
- just like a mirror, a lens is either convex or concave, depending on its shape.
Convex Lenses
- A convex lens is thicker in the middle and thinner at the edges.
- As light passes through he lens, it refracts towards the center of the lens.
- the more curved the lens is, the more the light refracts.
A convex lens can...
and...
- produce either a virtual image or a real image depending on where the objects is located relative to the focal point of the lens.
- if the object is located relative to the focal point, then a virtual image forms.
- this image is larger than the actual object. The image may have been observed with a magnifying glass.
- if the object is farther away from he lens than the focal point is, then a real image forms.
- the image can be larger, smaller, or the same size as the object.
Convex vs Concave
Compare
- Both a convex lens and a concave mirror are designed to
- focus light,
- and the type of image formed depends on the location of the object compared to the location of the focal point.
How does comparing items differ from contrasting them?
Student Discourse
Comparing is observing how things are alike.
Contrasting is observing how they are different.
Answer
Concave lenses...
- Concave lenses are thinner at the center than they are at the edges.
- When light rays travel through the lens, the rays
- rays are bent away from the optical axis, so the rays never meet.
- Because the rays never meet, concave lenses form only virtual images, and these images are upright and smaller than the objects.
Concave Lenses
Compare & Contrast
Check Point
In what ways is a convex lens like a concave mirror? In what ways is it different?
Answer
- Both concave mirrors and convex lenses focus light
- Type of image formed depends on the location of the objected compared to the focal point
- A mirror reflects light
- A lens refracts light
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