Dow Now What do you already know about light and how it moves?

Dow Now

• What do you already know about light and how it moves?

Essential Question• How does light move and change?

• What are convex and concave mirrors?

• What is the law of reflection?

Properties of Light

Objective• Students will learn to predict the direction in which light will

refract when it passes from one transparent material to another.

• Students will learn to apply the law of reflection and law of refraction to demonstrate everyday phenomena

• Students will learn to determine whether light is reflected, transmitted, and/or absorbed by a given object or material.

Properties of Light

Transparent

Translucent

Opaque

Properties of Light

Law of reflection

Refraction

• Light is a form of energy that travels in waves.

• Light waves spread out as they move away from a source.

• Light travels in straight lines called rays.

How does light travel?

• Light waves can carry energy through space and some matter.

• A light ray will not change direction unless it travels through a different medium or is disturbed in some way.

How does light travel? (cont.)

• Transparent allowing light to pass through with almost no distortion.• Objects look clear and crisp behind transparent

material. • Ex. Lens in eyeglasses


• Translucent allowing some light to travel through and blocking some light or bouncing it in a different direction. – Objects appear blurred behind translucent

material.– Ex. Stained glass, lampshades


• Opaque not allowing light to pass through. – Object is not seen behind opaque material.– Casts a shadow when it is in front of a light

source.– Ex. Books, walls, glass of milk


• Law of reflection is a physical law that states that the angle between an incoming light ray and a surface is equal to the angle between the reflected light ray and the same surface.

How does light act with mirrors?

Types of Mirrors• Any surface that reflects light and forms images is a

mirror• Plane mirror – has a flat surface. The images appear to be

exact copies, though they are reversed. • Concave mirror- has a surface that caves/curves inward• Convex mirror- has a surface that curves outward

– What everyday object has both a concave side and convex side?

• Refraction is the change in direction of a wave because of a change in the medium it is traveling through.

• When light moves into a medium where its speed decreases, the ray bends toward the normal.

What is refraction? (cont.)

• When light moves into a medium where its speed increases, the ray bends away from the normal.

• The larger the change in speed of the light wave is, the larger the change in direction is.


Types of Lenses• A lens that is thicker in the middle than

at the edges is a convex lens. • A lens that is thicker at the edges than

in the middle is a concave lens.• Lenses are used to correct vision

Closing Review

• What key vocabulary did we discuss today?• What is the difference between concave and

convex?• What is the law of reflection and refraction?

Do Now

• Explain the difference between reflection and refraction?

• What is a convex mirror? Concave?

Yesterday we learned

• Light is a form of energy that travels in waves• The difference between transparent,

translucent, and opaque materials• Law of reflection and refraction

Essential Question• How does light travel?

• Explain how light act with mirrors.

• Explain the difference between the three different types of mirrors.

Properties of Light

Objective• Students will learn to predict the

direction in which light will travel and the direction of reflection..

Properties of Light

How does light travel?• Light travels in straight lines (rays).• Light can travel through empty space without

needing a medium to pass through. • Light is affected by the materials it passes

through– Transparent– Translucent– Opaque

What is the difference between transparent, translucent and opaque?

How does light act with mirrors?

• Law of reflection: light will reflect at the same angel as the incoming angel

Plane mirror

• Any surface that reflects light and forms images is a mirror. Dull or rough surfaces do not reflect an image– Plane mirror – has a flat surface. The images

appear to be exact copies, though they are reversed.

– If you raise your left hand in front of a mirror, what happens to your reflection?

How does light act with mirrors? (cont.)

– Concave mirror • has a surface that curves inward or away from you ) • Light rays are reflected and meet at a point located in

front of the mirror dependent on the curve of the mirror.

• An object placed close to a concave mirror will produce a large image that right-side-up.

• As you move the object away, the image will become blurry, smaller and eventually appear upside down.


– Concave mirror Common Uses • Are used to gather light inside of telescopes. • Used in make-up or shaving mirrors – to make the face

appear larger and in more detail.


– Convex mirror • has a surface that curves outward or towards you.• Light rays are reflected from the surface and spread

out, producing a wide-angle view. • Always produces an image that is right-side-up and

much smaller than the object.


– Convex mirror Common Use • Useful for security in stores and providing a better

view for drivers of vehicles.


Light Optics Video

• Put your name at the top of the worksheet• Complete the worksheet as you watch the

video• Voices at a level 0

Essential Question Review Quiz• Answer the following questions using the

knowledge gain in todays lesson. – How does light travel?– Explain how light act with mirrors.– Explain the difference between the three different

types of mirrors.

Do Now

• What type of mirror is used to gather light inside a telescope? (Concave or convex)

• Light always travels through empty space at the same speed – 300,000km/s

• However, light travels slower when it moves through a medium, such as air, glass or water.

What is refraction?

• Refraction is the change in direction of a wave because of a change in the medium it is traveling through.

• When light moves into a medium where its speed decreases, the ray bends toward the normal.


• When light moves into a medium where its speed increases, the ray bends away from the normal.

• The larger the change in speed of the light wave is, the larger the change in direction is.


• A lens is a transparent object with at least one curved side that causes light to change direction.

• Light refracts as it passes through a lens.• The greater the curve of the lens, the more

the light refracts.


• A lens that is thicker in the middle than at the edges is a convex lens.

• A lens that is thicker at the edges than in the middle is a concave lens.


• A convex lens refracts light inward and it converges.

• If the object is located between the lens and its focal point, the image is right-side-up and larger than the object.

• If the object is located beyond the focal point, the image is upside down and smaller than the object.


• A concave lens refracts light rays apart. It diverges.• A concave lens is thinner in the middle than it is at

the edges. • The image is always right-side-up and smaller than

the actual object.


• Much of what is known about the universe has come from images and other information gathered by telescopes.

• A telescope is a device that collects light and magnifies images to make distant objects appear closer.

• Telescopes use mirrors and lenses to gather light.

How is light refracted by telescopes and cameras?

• Refracting telescopes use two convex lenses to form an image of a distant object.


• Light passes through an objective lens that forms an image.

• The image is then magnified by a lens in the eyepiece.

• Reflecting telescopes have a concave mirror instead of a concave objective lens to gather light.


• The large concave mirror focuses light onto a secondary mirror that directs it to the eyepiece, which magnifies the image.

• Cameras have a lens or a system of lenses that converge light rays toward a sensor.

• On some cameras, you can zoom, or make the image larger, by moving the lenses, which changes the focal length of the lens and lets you photograph distant and close objects.


• The internal shape of your eyes plays a role in how they function.

• If your eye shape is even slightly off, your vision will be impaired.

How can we correct vision?

• A nearsighted person has at least one eye that is longer than normal from front to back.

• This causes light rays from distant objects to be focused in front of the retina. As a result nearby objects are clear but distant objects look blurry.

How can we correct vision? (cont.)

• Concave lenses spread the light rays before they reach the eye so the rays travel a longer distance and focus at the correct spot.


• A farsighted person has at least one eye that is shorter than normal from front to back.

• This causes light rays from nearby objects to be focused in behind the retina. As a result, distant objects are clear but nearby objects look blurry.


• Convex lenses bend the light rays closer together before they reach the eye so the rays are focused properly on the retina.


Critical Thinking

• How do sunglasses work to protect your eyes?

Review

• file:///Users/MrMac/Documents/jppss/FORD/2014-2015HFMS/Science%20Resources%20/light/properties%20of%20light%20review.webarchive

Do Now

• List any remaining questions you have about light.

• Review for test on sound and light

Dow Now What do you already know about light and how it moves?

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