Refraction and Lenses

Chapter 9 lesson 3

• SC. 7. N. 1. 6: Explain that empirical evidence is the cumulative bod of observations of a natural phenomenon on which scientific explanations are based.

• SC. 7. N. 1. 7: Explain that scientific knowledge is the result of a great deal of debate and confirmation within the scientific community.

• SC. 7. N. 2. 1: Identify an instance from the history of science in which scientific knowledge had changed when new evidence or new interpretations are encountered.

• SC. 7.N. 10. 2: Observe and explain that light can be reflecte3d, refracted, and/ or absorbed.

• MA. 6. A. 3. 6.: Analyze tables to describe simple relations using common language.

Sunshine State Standards

Lesson 2 Review(KNOW THIS)• Light can hit an object and be reflected.• If the surface is smooth and flat the rays creating

a regular reflection.• If the surface is uneven the rays reflect creating a

diffuse reflection.• Mirrors can be flat, concave, or convex.• Images that are produced by mirrors can either

be real or virtual.• Virtual images are upright and real images are

upside down b/c the rays cross at the focal point.

What happens when light hits an object?

• Not all light that hits an object is reflected back, some objects absorb and/or refract light.

• Transparent matter (air, water, and glass) allow light to travel through.

• Refraction - Light travels from one medium to another and bends at different angles (slows down or speeds up).

• Mediums can include glass, air, and water.

Refraction• Light also goes through some things

– glass, water, eyeball, air• The presence of material slows light’s progress

– interactions with electrical properties of atoms• The “light slowing factor” is called the index of refraction

– glass has n = 1.52, meaning that light travels about 1.5 times slower in glass than in vacuum

– water has n = 1.33– air has n = 1.00028– vacuum is n = 1.00000 (speed of light at full capacity)

Index of Refraction• The measure of how

much a light ray bends when it enters that medium.

• Matter with a higher index of refraction bends light more than matter with a lower index of refraction.

DO NOT DRAW THIS IMAGE

Refraction of light traveling through different mediums

The light slows down and bends as it travels from air into water.

The light slows down and bends again as it travels from water to glass.

As the light travels back into the air it speeds up again and returns to its original angle of impact.

RAINBOWS AND PRISMS• White (visible) light is made of ROYGBIV light at different wavelengths.

• When light hits a prism the different wavelengths are refracted at different amounts; the shorter the wavelength, the more it refracts. • Red has longest wavelength, refracts the least. Violet has

shortest wavelength, refracts the most.

• Rainbows are created b/c water droplets are tiny prisms that refract (bend) the light into the full color spectrum.

Mirage

• An image of a distant object caused by the refraction of light.

• A mirage is an image of a real object formed by bending light.

• When the temperature is hot the air closer to the ground heats up. This hot air allows the light to travel faster and refract up into your line of sight.

• Appears to be a wet and glossy reflection from a smooth surface.

Lens• A lens is a curved piece of transparent

material that refracts light.

• Like mirrors the type of image that is formed by a lens depends on the type/shape of the lens.

Concave and Convex lens• Concave:

– A concave lens is thinner in the center then at than at the edges.

– The light rays bend that go through a concave lens bend away from the optical axis, form a smaller virtual image.

• Convex:– A convex lens is thicker in the center then at the edges.– Light rays that go through the convex lens bend toward

the optical axis and produces both a virtual and real image.

– The real image is upside down (further from focal point), the virtual image is right-side up (closer than focal point)

Concave Lenses

• Lenses that are thicker at the edges and thinner in the center.

– Diverges light rays – All images are

up right and reduced.

The De-Magnifier

DRAW THIS!!!

Convex Lenses

Thicker in the center than edges. – Lens that converges

(brings together) light rays.

– Forms real images and virtual images depending on position of the object

The Magnifier

DRAW THIS!!!

How You See

• Near Sighted – Eyeball is too long and image focuses in front of the retina

• Near Sightedness – Concave lenses expand focal length

• Far Sighted – Eyeball is too short so image is focused behind the retina

• Far Sightedness – Convex lens shortens the focal length.

Bill Nye Refraction Video

• http://www.teachertube.com/viewVideo.php?video_id=107503&title=bill_nye_science_guy___refraction_2_3&ref=Apbraget